The Boeing 777-200

Type  

Long and ultra long range widebody airliners

 

Schematics  

 

 

History  

Boeing’s advanced widebody 777 twin incorporates more advanced technologies than any other previous Boeing airliner, and has been progressively developed into increasingly longer range developments.

 

The 777 was originally conceived as a stretched 767, but Boeing instead adopted an all new design. Notable 777 design features include a unique fuselage cross section, Boeing’s first application of fly-by-wire, an advanced technology glass flightdeck with five liquid crystal displays, comparatively large scale use of composites (10% by weight), and advanced and extremely powerful engines. The 777 was also offered with optional folding wings where the outer 6m/21ft of each would fold upwards for operations at space restricted airports.

 

The basic 777-200 as launched in October 1990 was offered in two versions, the basic 777-200 (initially A-Market) and the increased weight longer range 777-200IGW (Increased Gross Weight, initially B-Market). The IGW has since been redesignated 777-200ER.

 

The 777-200 first flew on June 12 1994, with FAA and JAA certification awarded on April 19 1995. The FAA awarded full 180 minutes ETOPS clearance for PW4074 -200s on May 30 that year. First customer delivery was to United Airlines in May 1995. The first 777-200IGW/ER was delivered to British Airways in February 1997.

 

The 777-100X was a proposed shortened ultra long range (16,000km/8635nm) model, dropped in favour of the 777-200LR (originally 777-200X) design study. Boeing claims the 777-200LR will be the longest ranging airliner, capable of flying 16,417km (8865nm) – 18 hours flying time. It will achieve this with awesomely powerful 489kN (110,000lb) thrust GE90-110B1 turbofans, a significantly increased max takeoff weight and optional auxiliary fuel tanks in the rear cargo hold. Other changes include 2m (6.5ft) raked wingtips, new main landing gear, structural strengthening and optional overhead crew and flight attendant rest stations above the cabin. The 777-200LR was launched in 2000, but is now delayed until 2006.

 

The stretched 777-300 is described separately.

Powerplants  

777-200 – Two 329kN (74,000lb) Pratt & Whitney PW4074 turbofans, or 334kN (75,000lb) General Electric GE90-75Bs, or 334kN (75,000lb) Rolls-Royce Trent 875s.
247 tonne MTOW version – Two 345kN (77,000lb) PW4077s, or 338kN (76,000lb) GE90-76Bs or 345kN (77,000lb) Trent 877s.
777-200ER – Two 374kN (84,000lb) PW4084s, or 378kN (85,000lb) GE90-85Bs, or 373kN (84,000lb) Trent 884s; or 400kN (90,000lb) class PW4090s, GE90-90B1s, or Trent 890s; or 409kN (92,000lb) GE90-92Bs.
777-200LR – Two 489kN (110,000lb) GE90-110B1s.

 

Performance  

Typical cruising speed 905km/h (490kt).
777-200 – Range 229 tonne MTOW 7000km (3780nm), 233 tonne MTOW 7778km (4200nm), 247 tonne MTOW range 9537km (5150nm).
777-200ER – 263 tonne MTOW range 11,037km (5960nm), 286 tonne MTOW range 14,316km (7730nm).
777-200LR – Max range 16,417km (8865nm)

 

Weights  

777-200 – Empty 139,025kg (306,500lb) or 139,160kg (306,800lb), max takeoff optionally 229,520kg (506,000lb), or 233,600kg (515,000lb), or 247,210kg (535,000lb).
777-200ER – Empty 142,430kg (314,000lb) with 374kN/84,000lb engines, 143,015kg (315,300lb) with 400kN/90,000lb engines, max takeoff optionally 263,085kg (580,000lb) or 286,897kg (632,500lb).
777-200LR – Max takeoff 341,105kg (752,000lb).

 

Dimensions  

777-200 – Wing span 60.93m (199ft 11in), or folded 47.32m (155ft 3in), length 63.73m (209ft 1in), height 18.51m (60ft 9in). Wing area 427.8m2 (4605sq ft).

 

Capacity  

Flightcrew of two. Passenger seating for 305 in three classes or up to 440. Underfloor capacity for up to 32 LD3 containers.

 

Production  

Total 777-200 orders received as of early 2003 452, with 379 delivered

AIRCRAFT GAS TURBINE ENGINES

ENGINE TYPES and APPLICATIONS

Introduction

Most of modern passenger and military aircraft are powered by gas turbine engines, which are also called jet engines. There are several types of jet engines, but all jet engines have some parts in common . Aircraft gas turbine engines can be classified according to (1) the type of compressor used and (2) power usage produces by the engine.
Compressor types are as follows:
1. Centrifugal flow
2. Axial flow
3. Centrifugal-Axial flow.
Power usage produced are as follows:
1. Turbojet engines
2. Turbofan engines.
3. Turboshaft engines.

Centrifugal Compressor Engines
Centrifugal flow engines are compress the air by accelerating air outward perpendicular to the longitudinal axis of the machine. Centrifugal compressor engines are divided into Single-Stage and Two-Stage compressor. The amount of thrust is limited because the maximum compression ratio.

  

Principal Adventages of Centrifugal Compressor
1. Light Weight
2. Simplicity
3. Low cost.

Axial Flow Compressor Engines
Axial flow compressor engines may incorporate one , two , or three spools (Spool is defined as a group of compressor stages rotating at the same speed) . Two spool engine , the two rotors operate independently of one another. The turbine assembly for the low pressure compressor is the rear turbine unit . This set of turbines is connected to the forward , low pressure compressor by a shaft that passes through the hollow center of the high pressure compressor and turbine drive shaft.

  

Advantages and Disadvantages
Advantages: Most of the larger turbine engines use this type of compressor because of its ability to handle large volumes of airflow and high pressure ratio.
Disadvantages: More susceptable to foreign object damage , Expensive to manufacture , and It is very heavy in comparision to the centrifugal compressor with the same compression ratio.

Axial-Centrifugal Compressor Engine
Centrifugal compressor engine were used in many early jet engines , the efficiency level of single stage centrifugal compressor is relatively low . The multi-stage compressors are some what better , but still do not match with axial flow compressors. Some small modern turbo-prop and turbo-shaft engines achieve good results by using a combination axial flow and centrifugal compressor such as PT6 Pratt and Whitney of canada which very popular in the market today and T53 Lycoming engine.

Characteristics and Applications

The turbojet engine : Turbojet engine derives its thrust by highly accelerating a mass of air , all of which goes through the engine. Since a high ” jet ” velocity is required to obtain an acceptable of thrust, the turbine of turbo jet is designed to extract only enough power from the hot gas stream to drive the compressor and accessories . All of the propulsive force (100% of thrust ) produced by a jet engine derived from exhaust gas.

The turboprop engine : Turboprop engine derives its propulsion by the conversion of the majority of gas stream energy into mechanical power to drive the compressor , accessories , and the propeller load. The shaft on which the turbine is mounted drives the propeller through the propeller reduction gear system . Approximately 90% of thrust comes from propeller and about only 10% comes from exhaust gas.
The turbofan engine : Turbofan engine has a duct enclosed fan mounted at the front of the engine and driven either mechanically at the same speed as the compressor , or by an independent turbine located to the rear of the compressor drive turbine . The fan air can exit seperately from the primary engine air , or it can be ducted back to mix with the primary’s air at the rear . Approximately morethan 75% of thrust comes from fan and less than 25% comes from exhaust gas.

The turboshaft engine : Turboshaft engine derives its propulsion by the conversion of the majority of gas stream energy into mechanical power to drive the compressor , accessories , just like the turboprop engine but The shaft on which the turbine is mounted drives something other than an aircraft propeller such as the rotor of a helicopter through the reduction gearbox . The engine is called turboshaft.

AIRCRAFT GAS TURBINE ENGINES

ENGINE THEORY

 :

OPERATION

The jet engines are essentially a machine designed for the purpose of producing high velocity gasses at the jet nozzle . The engine is started by rotating the compressor with the starter , the outside air enter to the engine . The compressor works on this incoming air and delivery it to the combustion or burner section with as much as 12 times or more pressure the air had at the front . At the burner or combustion section , the ignition is igniting the mixture of fuel and air in the combustion chamber with one or more igniters which somewhat likes automobile spark plugs. When the engine has started and its compressor is rotating at sufficient speed , the starter and igniters are turn off. The engine will then run without further assistance as long as fuel and air in the proper proportions continue to enter the combustion chamber. Only 25% of the air is taking part in the actual combustion process . The rest of the air is mixed with the products of combustion for cooling before the gases enter the turbine wheel . The turbine extracts a major portion of energy in the gas stream and uses this energy to turn the compressor and accessories . The engine’s thrust comes from taking a large mass of air in at the front and expelling it at a much higher speed than it had when it entered the compressor . THRUST , THEN , IS EQUAL TO MASS FLOW RATE TIMES CHANGE IN VELOCITY .

The more air that an engine can compress and use , the greater is the power or thrust that it can produce . Roughly 75% of the power generated inside a jet engine is used to drive the compressor . Only what is left over is available to produce the thrust needed to propel the airplane .

JET ENGINE EQUATION

Since Fuel flow adds some mass to the air flowing through the engine , this must be added to the basic of thrust equation . Some formular do not consider the fuel flow effect when computing thrust because the weight of air leakage is approximately equal to the weight of fuel added . The following formular is applied when a nozzle of engine is ” choked ” , the pressure is such that the gases are treveling through it at the speed of sound and can not be further accelerated . Any increase in internal engine pressure will pass out through the nozzle still in the form of pressure . Even this pressure energy cannot turn into velocity energy but it is not lost .

FACTORS AFFECTING THRUST

The Jet engine is much more sensitive to operating variables . Those are:
1.) Engine rpm.
2.) Size of nozzle area.
3.) Weight of fuel flow.
4.) Amount of air bled from the compressor.
5.) Turbine inlet temperature.
6.) Speed of aircraft (ram pressure rise).
7.) Temperature of the air.
8.) Pressure of air
9.) Amount of humidity.
Note ; item 8,9 are the density of air .

ENGINE STATION DESIGNATIONS

Station designations are assigned to the varius sections of gas turbine engines to enable specific locations within the engine to be easily and accurately identified. The station numbers coincide with position from front to rear of the engine and are used as subscripts when designating different temperatures and pressures at the front , rear , or inside of the engine. For engine configurations other than the picture below should be made to manuals published by the engine manufacturer.


N = Speed ( rpm or percent )
N1 = Low Compressor Speed
N2 = High Compressor Speed
N3 = Free Turbine Speed
P = Pressure
T = Temperature
t = Total
EGT = Exhaust Gas Temperature
EPR = Engine Pressure Ratio ( Engine Thrust in term of EPR ). Pt7 / Pt2
Ex.: Pt
2 = Total Pressure at Station 2 ( low pressure compressor inlet )
Pt 7 = Total Pressure at Station 7 ( turbine discharge total pressure )

ENGINE THEORY

 :

OPERATION

The jet engines are essentially a machine designed for the purpose of producing high velocity gasses at the jet nozzle . The engine is started by rotating the compressor with the starter , the outside air enter to the engine . The compressor works on this incoming air and delivery it to the combustion or burner section with as much as 12 times or more pressure the air had at the front . At the burner or combustion section , the ignition is igniting the mixture of fuel and air in the combustion chamber with one or more igniters which somewhat likes automobile spark plugs. When the engine has started and its compressor is rotating at sufficient speed , the starter and igniters are turn off. The engine will then run without further assistance as long as fuel and air in the proper proportions continue to enter the combustion chamber. Only 25% of the air is taking part in the actual combustion process . The rest of the air is mixed with the products of combustion for cooling before the gases enter the turbine wheel . The turbine extracts a major portion of energy in the gas stream and uses this energy to turn the compressor and accessories . The engine’s thrust comes from taking a large mass of air in at the front and expelling it at a much higher speed than it had when it entered the compressor . THRUST , THEN , IS EQUAL TO MASS FLOW RATE TIMES CHANGE IN VELOCITY .

The more air that an engine can compress and use , the greater is the power or thrust that it can produce . Roughly 75% of the power generated inside a jet engine is used to drive the compressor . Only what is left over is available to produce the thrust needed to propel the airplane .

JET ENGINE EQUATION

Since Fuel flow adds some mass to the air flowing through the engine , this must be added to the basic of thrust equation . Some formular do not consider the fuel flow effect when computing thrust because the weight of air leakage is approximately equal to the weight of fuel added . The following formular is applied when a nozzle of engine is ” choked ” , the pressure is such that the gases are treveling through it at the speed of sound and can not be further accelerated . Any increase in internal engine pressure will pass out through the nozzle still in the form of pressure . Even this pressure energy cannot turn into velocity energy but it is not lost .

FACTORS AFFECTING THRUST

The Jet engine is much more sensitive to operating variables . Those are:
1.) Engine rpm.
2.) Size of nozzle area.
3.) Weight of fuel flow.
4.) Amount of air bled from the compressor.
5.) Turbine inlet temperature.
6.) Speed of aircraft (ram pressure rise).
7.) Temperature of the air.
8.) Pressure of air
9.) Amount of humidity.
Note ; item 8,9 are the density of air .

ENGINE STATION DESIGNATIONS

Station designations are assigned to the varius sections of gas turbine engines to enable specific locations within the engine to be easily and accurately identified. The station numbers coincide with position from front to rear of the engine and are used as subscripts when designating different temperatures and pressures at the front , rear , or inside of the engine. For engine configurations other than the picture below should be made to manuals published by the engine manufacturer.


N = Speed ( rpm or percent )
N1 = Low Compressor Speed
N2 = High Compressor Speed
N3 = Free Turbine Speed
P = Pressure
T = Temperature
t = Total
EGT = Exhaust Gas Temperature
EPR = Engine Pressure Ratio ( Engine Thrust in term of EPR ). Pt7 / Pt2
Ex.: Pt
2 = Total Pressure at Station 2 ( low pressure compressor inlet )
Pt 7 = Total Pressure at Station 7 ( turbine discharge total pressure )

Aero Engine Triple Spool Design minimize Engine Surges is the majar advantage of 3 Spool Concept

Major advantage of triple spool design is it’s ability to minimize engine surges thus they are the most efficient engine flying.

As mentioned by JETPILOT, namely that the more spools you have, the better because then they will be allowed to spin at their own speed given their spool mass.

Let’s say you’re at takeoff power with for example a double spool engine. The heavy N1 spool is turning at it’s own RPM and so is the lighter N2. Now you chop off the power. The lighter N2 will drop in RPM much quicker then the heavy N1 with it’s huge fan. So what happens is that the N1 compressors are feeding way too much air to the second (HP) compressor.

Where is all that excess air gonna go ?
Well in extreme cases you can have a very damaging engine surge in which air will flow in the wrong way through the engine. Most of todays engines have very sophisticated computer controlled “bypass doors” that let the air escape from the compressor casing.
But the chance of engine surges always remains. If you have three spools, the weight difference is spread over 3 spools thus drastically reducing the chance of engine surges

Aircraft Maintenance Engineering 3-Spool-Engine Concept

Aircraft Engine Maintenance 3-Spool-Engine Concepts

What is triple spool design on the RB211? what are the advantages/disadvantages?

A 3 spool engine is one that has three sets of compressors before the combustor and three sets of turbines behind it.

A spool is made up of a compressor and a corresponding turbine used to extract the power from the exhaust gasses to turn the compressor.

Each spool is given a name. N1, N2, and N3. N1 is the large fan section in front of the engine. N2 is the low pressure compressor section. And N3 is the high pressure compressor section. Some engines incorporate N2 And N3 into one rotating mass and call it N2. Hence the double spool engine.

Each section of the compressor wants to rotate at it’s own speed, and if allowed to do so as in a triple spool engine, it is able to operate more efficiently. It can turn at it’s optimum speed, and not have to compromise between the optimum speed for the N2 and N3 sections when attached in the double spool engine.

All modern engine have 2 sets of compressors (HP and LP) and a fan section providing a vast majority of the thrust.

In a 2 spool motor the HP section and the LP section are joined. The number of spools in an engine tells how many sets of compressor blades and corresponding sets of turbine blades the engine has. A single spool engine has one set of each, a double spool engine has two sets of each, and a triple spool engine has three sets of each.

3 Spool Engine advantages and disadvantages:

  • More sets of blades results in a greater engine weight, but the corresponding increase in thrust possible more than offsets the weight increase.

The drawbacks of a 3 spool engine are increased weight, complexity, and cost to purchase and overhaul, but they are the most efficient engine flying.

Aircraft Maintenance Engineering 3-Spool-Engine Concept

Wednesday , Posted by AME at 6:27 AM

Aircraft Engine Maintenance 3-Spool-Engine Concepts

What is triple spool design on the RB211? what are the advantages/disadvantages?

A 3 spool engine is one that has three sets of compressors before the combustor and three sets of turbines behind it.

A spool is made up of a compressor and a corresponding turbine used to extract the power from the exhaust gasses to turn the compressor.

Each spool is given a name. N1, N2, and N3. N1 is the large fan section in front of the engine. N2 is the low pressure compressor section. And N3 is the high pressure compressor section. Some engines incorporate N2 And N3 into one rotating mass and call it N2. Hence the double spool engine.

Each section of the compressor wants to rotate at it’s own speed, and if allowed to do so as in a triple spool engine, it is able to operate more efficiently. It can turn at it’s optimum speed, and not have to compromise between the optimum speed for the N2 and N3 sections when attached in the double spool engine.

All modern engine have 2 sets of compressors (HP and LP) and a fan section providing a vast majority of the thrust.

In a 2 spool motor the HP section and the LP section are joined. The number of spools in an engine tells how many sets of compressor blades and corresponding sets of turbine blades the engine has. A single spool engine has one set of each, a double spool engine has two sets of each, and a triple spool engine has three sets of each.

3 Spool Engine advantages and disadvantages:

  • More sets of blades results in a greater engine weight, but the corresponding increase in thrust possible more than offsets the weight increase.

The drawbacks of a 3 spool engine are increased weight, complexity, and cost to purchase and overhaul, but they are the most efficient engine flying.

Power Plant – B737

History

The original choice of powerplant was the Pratt & Whitney JT8D-1, but before the first order had been finalised the JT8D-7 was used for commonality with the current 727. The -7 was flat rated to develop the same thrust (14,000lb.st) at higher ambient temperatures than the -1 and became the standard powerplant for the -100. By the end of the -200 production the JT8D-17R was up to 17,400lb.st. thrust.

Auxiliary inlet doors were fitted to early JT8D’s around the nose cowl. These were spring loaded and opened automatically whenever the pressure differential between inlet and external static pressures was high, ie slow speed, high thrust conditions (takeoff) to give additional engine air and closed again as airspeed increased causing inlet static pressure to rise.

JT8D Cutaway

The sole powerplant for all 737′s after the -200 is the CFM-56. The core is produced by General Electric and is virtually identical to the F101 as used in the Rockwell B-1. SNECMA produce the fan, IP compressor, LP turbine, thrust reversers and all external accessories. The name “CFM” comes from GE’s commercial engine designation “CF” and SNECMA’s “M” for Moteurs.CFM 56 - 3 Cutaway

One problem with such a high bypass engine was its physical size and ground clearance; this was overcome by mounting the accessories on the lower sides to flatten the nacelle bottom and intake lip to give the “hamster pouch” look. The engines were moved forward and raised, level with the upper surface of the wing and tilted 5 degrees up which not only helped the ground clearance but also directed the exhaust downwards which reduced the effects of pylon overheating and gave some vectored thrust to assist take-off performance. The CFM56-3 proved to be almost 20% more efficient than the JT8D.

The NG’s use the CFM56-7B which has a 61 inch diameter solid titanium wide-chord fan, new LP turbine turbomachinery, FADEC, and new single crystal material in the HP turbine. All of which give an 8% fuel reduction, 15% maintenance cost reduction and greater EGT margin compared to the CFM56-3.

One of the most significant improvements in the powerplant has been to the noise levels. The original JT8D-9 engines in 1967 produced 75 decibel levels, enough to disrupt normal conversation indoors, within a noise contour that extended 12 miles along the take-off flight path. Since 1997 with the introduction of the 737-700’s CFM56-7B engines, the 75-decibel noise contour is now only 3.5 miles long.

The core engine (N2) is governed by metering fuel (see below), whereas the fan (N1) is a free turbine. The advantages of this include: minimised inter-stage bleeding, fewer stalls or surges and an increased compression ratio without decreasing efficiency.

This quote from CFMI in 1997:

“Since entering service in 1984, the CFM56-3 has established itself as the standard against which all other engines are judged in terms of reliability, durability, and cost of ownership. The fleet of nearly 1,800 CFM56-3-powered 737s in service worldwide have logged more than 61 million hours and 44 million cycles while maintaining a 99.98 percent dispatch reliability rate (one flight delayed or cancelled for engine-caused reasons per 5,000 departures), a .070 shop visit rate (one unscheduled shop visit per 14,286 flight hours), and an in-flight shutdown rate of .003 (one incident per 333,333 hours).”

Tech Insertion

“Tech Insertion” is an upgrade to the CFM56-5B & 7B available from early 2007. The package includes improvements to the HP compressor, combustor and HP & LP turbines. The package give a longer time on wing, about 5% lower maintenance costs, 15-20% lower oxides of nitrogen (NOx) emissions, and 1% lower fuel burn.

Tech Insertion will become the new production configuration for both the CFM56-7B and CFM56-5B. CFM is also defining potential upgrade kits that could be made available to operators by late 2007.

CFM56-7BE “Evolution”

The new CFM56-7BE Product Improvement package announced in 2009 will have the following design changes & improvements:

  • HPC outlet guide vane diffuser area ratio improved and pressure losses reduced.
  • HPT blades numbers reduced, axial chord increased, tip geometry improved. Rotor redesigned.
  • LPT blade & vane numbers reduced and profiles based on optimized loading distribution. LEAP56 incorporated.
  • Primary nozzle, plug & strut faring all redesigned.

The -7BE will be able to be intermixed with regular SAC/DAC or Tech Insertion engines subject to updated FMC, MEDB and EEC. Entry into service is planned for mid-2011

From the press 2 Aug 2010:

CFM International has won certification for its upgraded CFM56-7BE engine from the FAA and the European Aviation Safety Agency (EASA), and is working with Boeing to prepare for flight tests on a Boeing 737 starting in the fourth quarter of this year.

Entry into service is planned for mid-2011 to coincide with 737 airframe improvements that, together with the engine upgrade, are designed to provide a 2% improvement in fuel consumption. CFM provisionally scheduled engine certification by the end of the third quarter, but says development, including recently completed flight tests, have progressed faster than expected. Improvements include a new high-pressure compressor outlet guide vane diffuser, high-pressure turbine blades, disks and forward outer seal. The package also includes a new design of low-pressure turbine blades, vanes and disk.

The first full CFM56-7BE type design engine completed ground testing in January 2010, and overall completed 390 hours of ground testing, says the Franco-U.S. engine maker. In addition, the upgraded CFM completed a 60-hour certification flight test program in May on GE’s modified 747 flying testbed in Victorville, Calif.

At the recent Farnborough International Airshow, company officials said discussions are continuing with Airbus about a possible upgrade for the CFM56-5B for the A320 family based on the same technology suite. A decision on whether or not an upgraded variant will be developed for Airbus will be finalized by year-end, adds the engine maker.

Fuel

Thrust (fuel flow) is controlled primarily by a hydro-mechanical MEC in response to thrust lever movement, as fitted to the original 737-1/200’s. In the –3/4/500 series, fuel flow is further refined electronically by the PMC, which acts without thrust lever movement. The 737-NG models go one stage further with FADEC (EEC).

The 3/4/500′s may be flown with PMC’s inoperative, but an RTOW penalty (ie N1 reduction) is imposed because the N1 section will increase by approximately 4% during take-off due to windmilling effects (FOTB 737-1, Jan 1985). This reduction should save reaching any engine limits. The thrust levers should not be re-adjusted during the take-off after thrust is set unless a red-line limit is likely to be exceeded, ie you should allow the N1′s to windmill up.

Fuel is heated to avoid icing by the returning oil in the MEC.

Oil

Oil pressure is measured before the bearings, where you need it; oil temperature on return, at its hottest; and oil quantity at the tank, which drops after engine start. Oil pressure is unregulated, therefore the yellow band (13-26psi) is only valid at take-off thrust whereas the lower red line (13psi) is valid at all times. If the oil pressure is ever at or below the red line, the LOW OIL PRESSURE light will illuminate and that engine should be shut down. NB on the 737-1/200 when the oil quantity gauge reads zero, there could still be up to 5 quarts present.

Ignition

There are two independent AC ignition systems, L & R. Starting with R selected on the first flight of the day provides a check of the AC standby bus, which would be your only electrical source with the loss of thrust on both engines and no APU. Normally, in-flight, no igniters are in use as the combustion is self-sustaining. During engine start or take-off & landing, GND & CONT use the selected igniters. In conditions of moderate or severe precipitation, turbulence or icing, or for an in-flight relight, FLT should be selected to use both igniters. NG aircraft: for in-flight engine starts, GRD arms both igniters.

The 737-NG’s allow the EEC to switch the ignition ON or OFF under certain conditions:

  • ON: For flameout protection. The EEC will automatically switch on both ignition systems if a flameout is detected.
  • OFF: For ground start protection. The EEC will automatically switch off both ignition systems if a hot or wet start is detected.

Note that older 737-200s have ignition switch positions named GRD, OFF, L IGN, R IGN and FLT while newer 737s use GRD, OFF, CONT and FLT. This is why QRH uses “ON” (eg in the One Engine Inop Landing checklist) to cover both LOW IGN & CONT for operators with mixed fleets consisting of old and new versions of the 737.

737-200 Ignition panel

Engine Starting

Min duct pressure for start (Classics only): 30psi at msl, -½psi per 1000ft pressure altitude. Max: 48psi.

Min 25% N2 (or 20% N2 at max motoring) to introduce fuel; any sooner could result in a hot start. Max motoring is when N2 does not increase by more than 1% in 5 seconds.

Aborted engine start criteria:

  • No N1 (before start lever is raised to idle).
  • No oil pressure (by the time the engine is stable).
  • No EGT (within 10 secs of start lever being raised to idle).
  • No increase, or very slow increase, in N1 or N2 (after EGT indication).
  • EGT rapidly approaching or exceeding 725˚C.

An abnormal start advisory does not by itself mean that you have to abort the engine start.

Starter cutout is approx 46% N2 -3/4/500; 56% N2 -NG’s.

Starter duty cycle is:

  • First attempt: 2mins on, 20sec off.
  • Second and subsequent attempts: 2mins on, 3mins off.

Do not re-engage engine start switch until N2 is below 20%.

During cold weather starts, oil pressure may temporary exceed the green band or may not show any increase until oil temperature rises. No indication of oil pressure by the time idle RPM is achieved requires an immediate engine shutdown. At low ambient temperatures, a temporary high oil pressure above the green band may be tolerated.

When starting the engines in tailwind conditions, Boeing recommends making a normal start. Expect a longer cranking time to ensure N1 is rotating in the correct direction before moving the start lever. A higher than normal EGT should be expected, yet the same limits and procedures should apply.

Upper DU

Lower DU

Upper DU in Compact Display mode

The Compact Display mode can only be shown when the MFD ENG button is pressed for the first time after the aircraft has been completely shut down. The photo shows this display with one engine started and nicely illustrates the blank parameters which are controlled by the EEC and hence are only displayed when the EEC powers up when the associated start switch is selected to GND. During start-up the EEC’s receive electrical power from the AC transfer busses, but their normal source of power are their own alternators which cut-in when N2 is above 15%.

-200Adv Engine Instruments

Round Dial -3/400 Engine Instruments

3/4/500 EIS
NG EIS

EIS Display

The introduction of Engine Instrument System (EIS) in late 1988 gave many advantages over the electromechanical instruments present since 1967. ie a 10lb weight reduction, improved reliability, reduction in power consumption, detection of impending abnormal starts, storage of exceedances and a Built In Test Equipment (BITE) check facility.

The BITE check is accessed by pressing a small recessed button at the bottom of each eis panel, this is only possible when both engines N1 are below 10%. Pressing these buttons will show an LED check during which the various checks are conducted. If any of the checks fail, the appropriate code will be shown in place of the affected parameters readout. The following codes are used:

Primary EIS BITE Codes
Code Fault
ROM Read Only Memory check
RAM Random Access Memory check
FDC Frequency to Digital Converter check
ENG Engine Identity Inputs (not fuel flow)
PWR Power Monitor
MMF Maint Module Fault (fuel flow only)
RTC Real Time Clock (fuel flow only)
ERF Exceedance RAM Full (fuel flow only)
A/D Analogue to Digital Converter (fuel flow only)
ARF ARINC Receiver Fault (fuel flow only)
uP Microprocessor

Any exceedance of either N1, N2 or EGT is recorded at 1 sec intervals in a non-volatile memory along with the fuel flow at the time, this data can be downloaded by connecting an ARINC 429 bus reader. Up to 10 minutes of data can be stored. The last exceedance is also put into volatile memory and can be read straight from the EIS before aircraft electrical power is removed. This is done by pressing the primary EIS BITE button twice within 2 seconds, this will then alternately display the highest reading and the duration of the exceedance in seconds.

Secondary EIS BITE Codes
Code Fault
0- Microprocessor
1- Program Memory
2- Random Access Memory check
3- Analogue to Digital Converter
4- Power Monitor
5- 400Hz Reference Voltage
6- ARINC Receiver Fault

 

Airborne Vibration Monitors (AVM)

All series of 737 have the facility for AVM although not all 737-200′s have them fitted. The early 737-1/200′s had two vibration pickup points; One at the turbine section and one at the engine inlet there was a selector switch so that the crew could choose which to monitor. Some even had a high and low frequency filter selection switch.

From Boeing Flt Ops Review, Feb 2003: “On airplanes with AVM procedures, flight crews should also be made aware that AVM indications are not valid while at takeoff power settings, during power changes, or until after engine thermal stabilization. High AVM indications can also be observed during operations in icing conditions.”

 

High Pressure Turbine Clearance Control

The HPTCC system uses HP compressor bleed air to obtain maximum steady state HPT performance and to minimise EGT transient overshoot during rapid change of engine speed.

Variable Stator Vanes

The VSV actuation system controls primary airflow through the HP compressor by varying the angle of the inlet guide vanes and three stages of variable stator vanes.

Variable Bleed Valves

Control airflow quantity to the HP compressor. They are fully open during rapid accelerations and reverse thrust operation.

 

Dual Annular Combustors (DAC)

The CFM56-7B is available with an optional DAC system, known as the CFM56-7B/2, which considerably reduces NOx emissions. DAC have 20 double tip fuel nozzles instead of the single tip and a dual annular shaped combustion chamber. The number of nozzles in use: 20/0, 20/10 or 20/20, varies depending upon thrust required. The precise N1 ranges of the different modes varies with ambient conditions.

  • 20/20 mode – High power (cruise N1 and above)
  • 20/10 mode – Medium power
  • 20/00 mode – Low power (Idle N1)

This gives a lean fuel/air mixture, which reduces flame temperatures, and also gives higher throughput velocities which reduce the residence time available to form NOx. The net result is up to 40% less NOx emissions than a standard CFM56-7.

The first were installed on the 737-600 fleet of SAS but unfortunately were subject to resonance in the LPT-1 blades during operation in the 20/10 mode, which occurred in an N1 range usually used during descent and approach. Although there were no in-flight shutdowns, boroscope inspections revealed that the LPT blades were starting to separate. CFM quickly replaced all blades on all DAC engines with reinforced blades and have since replaced them again with a new redesigned blade.

 

Reverse Thrust

The original 737-1/200 thrust reversers were pneumatically powered clamshell doors taken straight from the 727 (shown left). When reverse was selected, 13th stage bleed air was ported to a pneumatic actuator that rotated the deflector doors and clamshell doors into position. Unfortunately they were relatively ineffective and apparently tended to push the aircraft up off the runway when deployed. This reduced the downforce on the main wheels thereby reducing the effectiveness of the wheel brakes.

By 1969 these had been changed by Boeing and Rohr to the much more successful hydraulically powered target type thrust reversers (shown right). This required a 48 inch extension to the tailpipe to accommodate the two cylindrical deflector doors which were mounted on a four bar linkage system and associated hydraulics. The doors are set 35 degrees away from the vertical to allow the exhaust to be deflected inboard and over the wings and outboard and under the wings. This ensures that exhaust and debris is not blown into the wheel-well, nor is it blown directly downwards which would lift the weight off the wheels or be re-ingested. Fortunately the new longer nacelle improved cruise performance by improving internal airflow within the engine and also reduced cruise drag. These thrust reversers are locked against inadvertent deployment by both deflector door locks and the four bar linkage being overcenter. To illustrate how poor the original clamshell system was, Boeings own data says target type thrust reversers at 1.5 EPR are twice as effective as clamshells at full thrust!

The CFM56 uses blocker doors and cascade vanes to direct fan air forwards. Net reverse thrust is defined as: fan reverser air, minus forward thrust from engine core, plus form drag from the blocker door. As this is significantly greater at higher thrust, reverse thrust should be used immediately after landing or RTO and, if conditions allow, should be reduced to idle by 60kts to avoid debris ingestion damage. Caution: It is possible to deploy reverse thrust when either Rad Alt is below 10ft – this is not recommended.

The REVERSER light shows either control valve or sleeve position disagreement or that the auto-restow circuit is activated. This light will illuminate every time the reverser is commanded to stow, but extinguishes after the stow has completed, and will only bring up master caution ENG if a malfunction has occurred. Recycling the reverse thrust will often clear the fault. If this occurs in-flight, reverse thrust will be available after landing.

The REVERSER UNLOCKED light (EIS panel) is potentially much more serious and will illuminate in-flight if a sleeve has mechanically unlocked. Follow the QRH drill, but only multiple failures will allow the engine to go into reverse thrust.

The 737-1/200 thrust reverser panel has a LOW PRESSURE light which refers to the reverser accumulator pressure when insufficient pressure is available to deploy the reversers. The blue caption between the switches is ISOLATION VALVE and illuminates when the three conditions for reverse thrust are satisfied: Engine running, Aircraft on ground & Fire switches in normal position. The guarded NORMAL / OVERRIDE switches to enable the reverse thrust to be selected on the ground with the engines stopped (for maintenance purposes).

 

 

HushKits

The first “hushkit” was not visible externally, in 1982 exhaust mixers were made available for the JT8D-15, -17 or -17R. These were fitted behind the LP turbine to mix the hot gas core airflow with the cooler bypassed fan air. This increased mixing reduced noise levels by up to 3.6 EPNdB.

Several different Stage III hushkits have been available from manufacturers Nordam (shown right) and AvAero since 1992. The Nordam comes in HGW and LGW versions.

As hushkits use more fuel, the EU tried to ban all hushkitted aircraft flying into the EU from April 2002. This was strongly opposed and the directive has been changed to allow hushkitted aircraft to use airports which will accept them.

737 classics may be fitted with hardwall forward acoustic panels which reduce noise by 1 EPNdB

 

Additional References

 

Limitations

Series 1/200 3/4/500 6/7/8/900/BBJ
Engine JT8-17A CFM56-3 CFM56-7
 
Max time limit for take-off or go-around thrust: 5 mins 5 mins * 5 mins *
Max N1 102.4% 106% 104%
Max N2 100% 105% 105%
 

Max EGT’s:

Take-off (5 min limit) 650°C 930°C 950°C
Continuous 610°C 895°C 925°C
Start 575°C 725°C 725°C
 

Oil T’s & P’s

Max temperature 165°C 165°C 155°C
15 minute limit (45 minute limit on NG) 130-165°C 160-165°C 140-155°C
Max continuous 130°C 160°C 140°C
Min oil press 40psi 13psi (warning light), 26psi (gauge) 13psi (warning light), 26psi (gauge)
Min oil quantity (at dispatch) 2.25 USG 60% full (12 US Quarts) ** 60% full (12 US Quarts) **
Starting pressures prior to starter engagement

30psi -1/2psi per 1000′ amsl

N/A
Starter duty cycle 1st attempt: 2min on, 20sec off

2nd & subsequent attempt: 2min on, 3min off

2mins on, 10secs off.
* May be increased to 10 mins if certified** See AMM Task 12-13-11-600-801

Engine Ratings

Maximum Certified Thrust – This is the maximum thrust certified during testing for each series of 737. This is also the thrust that you get when you firewall the thrust levers, regardless of the maximum rated thrust.

On the 737NG, the EEC limits the maximum certified thrust gained from data in the engine strut according to the airplane model as follows:

Aircraft Series Maximum Certified Thrust
737-600 CFM56-7B22 = 22,700lb.st
737-700 CFM56-7B24 = 24,200lb.st
737-800 CFM56-7B27 = 27,300lb.st
737-900 CFM56-7B27 = 27,300lb.st

 

Maximum Rated Thrust – This is the maximum thrust for the installed engine that the autothrottle will command. This is specified by the operator from the options in the table below.

Engine Aircraft Series Max Static Thrust (lb.st.) Bypass Ratio EGT Margin (C)
JT8D-7/7A/7B 1/200 14,000 1.10
JT8D-9/9A 1/200 14,500 1.04
JT8D-15/15A 200Adv 15,500 0.99
JT8D-17/17A 200Adv 16,000 1.02
JT8D-17R 200Adv 17,400 1.00
CFM56-3B4 500 18,500 5.0 90
CFM56-3B1 3/500 20,000 5.0 70
CFM56-3B2 3/400 22,000 5.0 50
CFM56-3C1 400 23,500 4.9 45
CFM56-7B18 600 19,500 5.5 145
CFM56-7B20 6/700 20,600 5.4 148
CFM56-7B22 6/700 22,700 5.3 150
CFM56-7B24 7/8/900 24,200 5.3 125
CFM56-7B26 7/8/900/BBJ 26,400 5.1 85
CFM56-7B27 8/900/BBJ 27,300 5.0 ?

Misc Photos

The left hand side of the CFM56-3. The large silver coloured pipe is the start air manifold with the starter located at its base. The black unit below that is the CSD. The green unit forward (left) of the CSD is the generator cooling air collector shroud, the silver-gold thing forward of that (with the wire bundle visible) is the generator, and the green cap most forward is the generator cooling air inlet.
The view into the JT8D jetpipe.The corrugated ring is the mixer unit, this is designed to thoroughly mix the bypass air with the turbine exhaust.

The exhaust cone makes a divergent flow which slows down the exhaust and also protects the rear face of the last turbine stage.

The view into the CFM56-3 jetpipe.This is the turbine exhaust area, no mixing is required as the bypass air is exhausted coaxially.
There are two fan inlet temperature sensors in the CFM56-3 engine intake. The one at the 2 o’clock position is used by the PMC and the one at the 11 o’clock position is used by the MEC. The MEC uses the signal to establish parameters to control low and high idle power schedules.The temperature data is used for thrust management and variable bleed valves, variable stator vanes & high / low pressure turbine clearance control systems.
The CFM56-7 inlet has just one fan inlet temperature probe, which is for the EEC (because there is no PMC on the NG’s).A subtle difference between the NG & classic temp probes is that the NG’s only use inlet temp data on the ground and for 5 minutes after take-off. In-flight after 5 minutes temp data is taken from the ADIRU’s.

The temperature data is used for thrust management and variable bleed valves, variable stator vanes & high / low pressure turbine clearance control systems.

The CFM56-7 spinner has a unique conelliptical profile. The first 737-3/400′s had a conical (sharp pointed) spinner but these tended to shed ice into the core. This was one of the reasons for the early limitation of minimum 45% N1 in icing conditions which made descent management quite difficult. They were later replaced with elliptical (round nosed) spinners which succeeded in deflecting the ice away from the core, but because of their larger stagnation point, were more prone to picking up ice in the first place. The conelliptical spinner of the NG’s neatly solves both problems.
The CFM56-7 tailpipe is slightly longer then the CFM56-3 and has a small tube protruding from the faring. This is the Aft Fairing Drain Tube for any hydraulic fluid, oil or fuel that may collect in there. There is also a second drain tube that does not protrude located on the inside of the fairing.
The JT8D tailpipe fitted as standard from l/n 135 onwards.The original thrust reversers were totally redesigned by Boeing and Rohr since the aircraft had inherited the same internal pneumatically powered clamshell thrust reversers as the 727 which were relatively ineffective and apparently tended to lift the aircraft off the runway when deployed! The redesign to external hydraulically powered target reversers cost Boeing $24 million but dramatically improved its short field performance which boosted sales to carriers proposing to use the aircraft as a regional jet from short runways. Also the engine nacelles were extended by 1.14m as a drag reduction measure.
The outboard side of the JT8D-9A with the cowling open.

istory

The original choice of powerplant was the Pratt & Whitney JT8D-1, but before the first order had been finalised the JT8D-7 was used for commonality with the current 727. The -7 was flat rated to develop the same thrust (14,000lb.st) at higher ambient temperatures than the -1 and became the standard powerplant for the -100. By the end of the -200 production the JT8D-17R was up to 17,400lb.st. thrust.

Auxiliary inlet doors were fitted to early JT8D’s around the nose cowl. These were spring loaded and opened automatically whenever the pressure differential between inlet and external static pressures was high, ie slow speed, high thrust conditions (takeoff) to give additional engine air and closed again as airspeed increased causing inlet static pressure to rise.

JT8D Cutaway

The sole powerplant for all 737′s after the -200 is the CFM-56. The core is produced by General Electric and is virtually identical to the F101 as used in the Rockwell B-1. SNECMA produce the fan, IP compressor, LP turbine, thrust reversers and all external accessories. The name “CFM” comes from GE’s commercial engine designation “CF” and SNECMA’s “M” for Moteurs.CFM 56 - 3 Cutaway

One problem with such a high bypass engine was its physical size and ground clearance; this was overcome by mounting the accessories on the lower sides to flatten the nacelle bottom and intake lip to give the “hamster pouch” look. The engines were moved forward and raised, level with the upper surface of the wing and tilted 5 degrees up which not only helped the ground clearance but also directed the exhaust downwards which reduced the effects of pylon overheating and gave some vectored thrust to assist take-off performance. The CFM56-3 proved to be almost 20% more efficient than the JT8D.

The NG’s use the CFM56-7B which has a 61 inch diameter solid titanium wide-chord fan, new LP turbine turbomachinery, FADEC, and new single crystal material in the HP turbine. All of which give an 8% fuel reduction, 15% maintenance cost reduction and greater EGT margin compared to the CFM56-3.

One of the most significant improvements in the powerplant has been to the noise levels. The original JT8D-9 engines in 1967 produced 75 decibel levels, enough to disrupt normal conversation indoors, within a noise contour that extended 12 miles along the take-off flight path. Since 1997 with the introduction of the 737-700’s CFM56-7B engines, the 75-decibel noise contour is now only 3.5 miles long.

The core engine (N2) is governed by metering fuel (see below), whereas the fan (N1) is a free turbine. The advantages of this include: minimised inter-stage bleeding, fewer stalls or surges and an increased compression ratio without decreasing efficiency.

This quote from CFMI in 1997:

“Since entering service in 1984, the CFM56-3 has established itself as the standard against which all other engines are judged in terms of reliability, durability, and cost of ownership. The fleet of nearly 1,800 CFM56-3-powered 737s in service worldwide have logged more than 61 million hours and 44 million cycles while maintaining a 99.98 percent dispatch reliability rate (one flight delayed or cancelled for engine-caused reasons per 5,000 departures), a .070 shop visit rate (one unscheduled shop visit per 14,286 flight hours), and an in-flight shutdown rate of .003 (one incident per 333,333 hours).”

Tech Insertion

“Tech Insertion” is an upgrade to the CFM56-5B & 7B available from early 2007. The package includes improvements to the HP compressor, combustor and HP & LP turbines. The package give a longer time on wing, about 5% lower maintenance costs, 15-20% lower oxides of nitrogen (NOx) emissions, and 1% lower fuel burn.

Tech Insertion will become the new production configuration for both the CFM56-7B and CFM56-5B. CFM is also defining potential upgrade kits that could be made available to operators by late 2007.

CFM56-7BE “Evolution”

The new CFM56-7BE Product Improvement package announced in 2009 will have the following design changes & improvements:

  • HPC outlet guide vane diffuser area ratio improved and pressure losses reduced.
  • HPT blades numbers reduced, axial chord increased, tip geometry improved. Rotor redesigned.
  • LPT blade & vane numbers reduced and profiles based on optimized loading distribution. LEAP56 incorporated.
  • Primary nozzle, plug & strut faring all redesigned.

The -7BE will be able to be intermixed with regular SAC/DAC or Tech Insertion engines subject to updated FMC, MEDB and EEC. Entry into service is planned for mid-2011

From the press 2 Aug 2010:

CFM International has won certification for its upgraded CFM56-7BE engine from the FAA and the European Aviation Safety Agency (EASA), and is working with Boeing to prepare for flight tests on a Boeing 737 starting in the fourth quarter of this year.

Entry into service is planned for mid-2011 to coincide with 737 airframe improvements that, together with the engine upgrade, are designed to provide a 2% improvement in fuel consumption. CFM provisionally scheduled engine certification by the end of the third quarter, but says development, including recently completed flight tests, have progressed faster than expected. Improvements include a new high-pressure compressor outlet guide vane diffuser, high-pressure turbine blades, disks and forward outer seal. The package also includes a new design of low-pressure turbine blades, vanes and disk.

The first full CFM56-7BE type design engine completed ground testing in January 2010, and overall completed 390 hours of ground testing, says the Franco-U.S. engine maker. In addition, the upgraded CFM completed a 60-hour certification flight test program in May on GE’s modified 747 flying testbed in Victorville, Calif.

At the recent Farnborough International Airshow, company officials said discussions are continuing with Airbus about a possible upgrade for the CFM56-5B for the A320 family based on the same technology suite. A decision on whether or not an upgraded variant will be developed for Airbus will be finalized by year-end, adds the engine maker.

Fuel

Thrust (fuel flow) is controlled primarily by a hydro-mechanical MEC in response to thrust lever movement, as fitted to the original 737-1/200’s. In the –3/4/500 series, fuel flow is further refined electronically by the PMC, which acts without thrust lever movement. The 737-NG models go one stage further with FADEC (EEC).

The 3/4/500′s may be flown with PMC’s inoperative, but an RTOW penalty (ie N1 reduction) is imposed because the N1 section will increase by approximately 4% during take-off due to windmilling effects (FOTB 737-1, Jan 1985). This reduction should save reaching any engine limits. The thrust levers should not be re-adjusted during the take-off after thrust is set unless a red-line limit is likely to be exceeded, ie you should allow the N1′s to windmill up.

Fuel is heated to avoid icing by the returning oil in the MEC.

Oil

Oil pressure is measured before the bearings, where you need it; oil temperature on return, at its hottest; and oil quantity at the tank, which drops after engine start. Oil pressure is unregulated, therefore the yellow band (13-26psi) is only valid at take-off thrust whereas the lower red line (13psi) is valid at all times. If the oil pressure is ever at or below the red line, the LOW OIL PRESSURE light will illuminate and that engine should be shut down. NB on the 737-1/200 when the oil quantity gauge reads zero, there could still be up to 5 quarts present.

Ignition

There are two independent AC ignition systems, L & R. Starting with R selected on the first flight of the day provides a check of the AC standby bus, which would be your only electrical source with the loss of thrust on both engines and no APU. Normally, in-flight, no igniters are in use as the combustion is self-sustaining. During engine start or take-off & landing, GND & CONT use the selected igniters. In conditions of moderate or severe precipitation, turbulence or icing, or for an in-flight relight, FLT should be selected to use both igniters. NG aircraft: for in-flight engine starts, GRD arms both igniters.

The 737-NG’s allow the EEC to switch the ignition ON or OFF under certain conditions:

  • ON: For flameout protection. The EEC will automatically switch on both ignition systems if a flameout is detected.
  • OFF: For ground start protection. The EEC will automatically switch off both ignition systems if a hot or wet start is detected.

Note that older 737-200s have ignition switch positions named GRD, OFF, L IGN, R IGN and FLT while newer 737s use GRD, OFF, CONT and FLT. This is why QRH uses “ON” (eg in the One Engine Inop Landing checklist) to cover both LOW IGN & CONT for operators with mixed fleets consisting of old and new versions of the 737.

737-200 Ignition panel

Engine Starting

Min duct pressure for start (Classics only): 30psi at msl, -½psi per 1000ft pressure altitude. Max: 48psi.

Min 25% N2 (or 20% N2 at max motoring) to introduce fuel; any sooner could result in a hot start. Max motoring is when N2 does not increase by more than 1% in 5 seconds.

Aborted engine start criteria:

  • No N1 (before start lever is raised to idle).
  • No oil pressure (by the time the engine is stable).
  • No EGT (within 10 secs of start lever being raised to idle).
  • No increase, or very slow increase, in N1 or N2 (after EGT indication).
  • EGT rapidly approaching or exceeding 725˚C.

An abnormal start advisory does not by itself mean that you have to abort the engine start.

Starter cutout is approx 46% N2 -3/4/500; 56% N2 -NG’s.

Starter duty cycle is:

  • First attempt: 2mins on, 20sec off.
  • Second and subsequent attempts: 2mins on, 3mins off.

Do not re-engage engine start switch until N2 is below 20%.

During cold weather starts, oil pressure may temporary exceed the green band or may not show any increase until oil temperature rises. No indication of oil pressure by the time idle RPM is achieved requires an immediate engine shutdown. At low ambient temperatures, a temporary high oil pressure above the green band may be tolerated.

When starting the engines in tailwind conditions, Boeing recommends making a normal start. Expect a longer cranking time to ensure N1 is rotating in the correct direction before moving the start lever. A higher than normal EGT should be expected, yet the same limits and procedures should apply.

Upper DU

Lower DU

Upper DU in Compact Display mode

The Compact Display mode can only be shown when the MFD ENG button is pressed for the first time after the aircraft has been completely shut down. The photo shows this display with one engine started and nicely illustrates the blank parameters which are controlled by the EEC and hence are only displayed when the EEC powers up when the associated start switch is selected to GND. During start-up the EEC’s receive electrical power from the AC transfer busses, but their normal source of power are their own alternators which cut-in when N2 is above 15%.

-200Adv Engine Instruments

Round Dial -3/400 Engine Instruments

3/4/500 EIS
NG EIS

EIS Display

The introduction of Engine Instrument System (EIS) in late 1988 gave many advantages over the electromechanical instruments present since 1967. ie a 10lb weight reduction, improved reliability, reduction in power consumption, detection of impending abnormal starts, storage of exceedances and a Built In Test Equipment (BITE) check facility.

The BITE check is accessed by pressing a small recessed button at the bottom of each eis panel, this is only possible when both engines N1 are below 10%. Pressing these buttons will show an LED check during which the various checks are conducted. If any of the checks fail, the appropriate code will be shown in place of the affected parameters readout. The following codes are used:

Primary EIS BITE Codes
Code Fault
ROM Read Only Memory check
RAM Random Access Memory check
FDC Frequency to Digital Converter check
ENG Engine Identity Inputs (not fuel flow)
PWR Power Monitor
MMF Maint Module Fault (fuel flow only)
RTC Real Time Clock (fuel flow only)
ERF Exceedance RAM Full (fuel flow only)
A/D Analogue to Digital Converter (fuel flow only)
ARF ARINC Receiver Fault (fuel flow only)
uP Microprocessor

Any exceedance of either N1, N2 or EGT is recorded at 1 sec intervals in a non-volatile memory along with the fuel flow at the time, this data can be downloaded by connecting an ARINC 429 bus reader. Up to 10 minutes of data can be stored. The last exceedance is also put into volatile memory and can be read straight from the EIS before aircraft electrical power is removed. This is done by pressing the primary EIS BITE button twice within 2 seconds, this will then alternately display the highest reading and the duration of the exceedance in seconds.

Secondary EIS BITE Codes
Code Fault
0- Microprocessor
1- Program Memory
2- Random Access Memory check
3- Analogue to Digital Converter
4- Power Monitor
5- 400Hz Reference Voltage
6- ARINC Receiver Fault

Airborne Vibration Monitors (AVM)

All series of 737 have the facility for AVM although not all 737-200′s have them fitted. The early 737-1/200′s had two vibration pickup points; One at the turbine section and one at the engine inlet there was a selector switch so that the crew could choose which to monitor. Some even had a high and low frequency filter selection switch.

From Boeing Flt Ops Review, Feb 2003: “On airplanes with AVM procedures, flight crews should also be made aware that AVM indications are not valid while at takeoff power settings, during power changes, or until after engine thermal stabilization. High AVM indications can also be observed during operations in icing conditions.”

High Pressure Turbine Clearance Control

The HPTCC system uses HP compressor bleed air to obtain maximum steady state HPT performance and to minimise EGT transient overshoot during rapid change of engine speed.

Variable Stator Vanes

The VSV actuation system controls primary airflow through the HP compressor by varying the angle of the inlet guide vanes and three stages of variable stator vanes.

Variable Bleed Valves

Control airflow quantity to the HP compressor. They are fully open during rapid accelerations and reverse thrust operation.

Dual Annular Combustors (DAC)

The CFM56-7B is available with an optional DAC system, known as the CFM56-7B/2, which considerably reduces NOx emissions. DAC have 20 double tip fuel nozzles instead of the single tip and a dual annular shaped combustion chamber. The number of nozzles in use: 20/0, 20/10 or 20/20, varies depending upon thrust required. The precise N1 ranges of the different modes varies with ambient conditions.

  • 20/20 mode – High power (cruise N1 and above)
  • 20/10 mode – Medium power
  • 20/00 mode – Low power (Idle N1)

This gives a lean fuel/air mixture, which reduces flame temperatures, and also gives higher throughput velocities which reduce the residence time available to form NOx. The net result is up to 40% less NOx emissions than a standard CFM56-7.

The first were installed on the 737-600 fleet of SAS but unfortunately were subject to resonance in the LPT-1 blades during operation in the 20/10 mode, which occurred in an N1 range usually used during descent and approach. Although there were no in-flight shutdowns, boroscope inspections revealed that the LPT blades were starting to separate. CFM quickly replaced all blades on all DAC engines with reinforced blades and have since replaced them again with a new redesigned blade.

Reverse Thrust

The original 737-1/200 thrust reversers were pneumatically powered clamshell doors taken straight from the 727 (shown left). When reverse was selected, 13th stage bleed air was ported to a pneumatic actuator that rotated the deflector doors and clamshell doors into position. Unfortunately they were relatively ineffective and apparently tended to push the aircraft up off the runway when deployed. This reduced the downforce on the main wheels thereby reducing the effectiveness of the wheel brakes.

By 1969 these had been changed by Boeing and Rohr to the much more successful hydraulically powered target type thrust reversers (shown right). This required a 48 inch extension to the tailpipe to accommodate the two cylindrical deflector doors which were mounted on a four bar linkage system and associated hydraulics. The doors are set 35 degrees away from the vertical to allow the exhaust to be deflected inboard and over the wings and outboard and under the wings. This ensures that exhaust and debris is not blown into the wheel-well, nor is it blown directly downwards which would lift the weight off the wheels or be re-ingested. Fortunately the new longer nacelle improved cruise performance by improving internal airflow within the engine and also reduced cruise drag. These thrust reversers are locked against inadvertent deployment by both deflector door locks and the four bar linkage being overcenter. To illustrate how poor the original clamshell system was, Boeings own data says target type thrust reversers at 1.5 EPR are twice as effective as clamshells at full thrust!

The CFM56 uses blocker doors and cascade vanes to direct fan air forwards. Net reverse thrust is defined as: fan reverser air, minus forward thrust from engine core, plus form drag from the blocker door. As this is significantly greater at higher thrust, reverse thrust should be used immediately after landing or RTO and, if conditions allow, should be reduced to idle by 60kts to avoid debris ingestion damage. Caution: It is possible to deploy reverse thrust when either Rad Alt is below 10ft – this is not recommended.

The REVERSER light shows either control valve or sleeve position disagreement or that the auto-restow circuit is activated. This light will illuminate every time the reverser is commanded to stow, but extinguishes after the stow has completed, and will only bring up master caution ENG if a malfunction has occurred. Recycling the reverse thrust will often clear the fault. If this occurs in-flight, reverse thrust will be available after landing.

The REVERSER UNLOCKED light (EIS panel) is potentially much more serious and will illuminate in-flight if a sleeve has mechanically unlocked. Follow the QRH drill, but only multiple failures will allow the engine to go into reverse thrust.

The 737-1/200 thrust reverser panel has a LOW PRESSURE light which refers to the reverser accumulator pressure when insufficient pressure is available to deploy the reversers. The blue caption between the switches is ISOLATION VALVE and illuminates when the three conditions for reverse thrust are satisfied: Engine running, Aircraft on ground & Fire switches in normal position. The guarded NORMAL / OVERRIDE switches to enable the reverse thrust to be selected on the ground with the engines stopped (for maintenance purposes).

HushKits

The first “hushkit” was not visible externally, in 1982 exhaust mixers were made available for the JT8D-15, -17 or -17R. These were fitted behind the LP turbine to mix the hot gas core airflow with the cooler bypassed fan air. This increased mixing reduced noise levels by up to 3.6 EPNdB.

Several different Stage III hushkits have been available from manufacturers Nordam (shown right) and AvAero since 1992. The Nordam comes in HGW and LGW versions.

As hushkits use more fuel, the EU tried to ban all hushkitted aircraft flying into the EU from April 2002. This was strongly opposed and the directive has been changed to allow hushkitted aircraft to use airports which will accept them.

737 classics may be fitted with hardwall forward acoustic panels which reduce noise by 1 EPNdB

Additional References

Limitations

Series 1/200 3/4/500 6/7/8/900/BBJ
Engine JT8-17A CFM56-3 CFM56-7
 
Max time limit for take-off or go-around thrust: 5 mins 5 mins * 5 mins *
Max N1 102.4% 106% 104%
Max N2 100% 105% 105%
Max EGT’s:
Take-off (5 min limit) 650°C 930°C 950°C
Continuous 610°C 895°C 925°C
Start 575°C 725°C 725°C
Oil T’s & P’s
Max temperature 165°C 165°C 155°C
15 minute limit (45 minute limit on NG) 130-165°C 160-165°C 140-155°C
Max continuous 130°C 160°C 140°C
Min oil press 40psi 13psi (warning light), 26psi (gauge) 13psi (warning light), 26psi (gauge)
Min oil quantity (at dispatch) 2.25 USG 60% full (12 US Quarts) ** 60% full (12 US Quarts) **
Starting pressures prior to starter engagement

30psi -1/2psi per 1000′ amsl

N/A
Starter duty cycle 1st attempt: 2min on, 20sec off

2nd & subsequent attempt: 2min on, 3min off

2mins on, 10secs off.
* May be increased to 10 mins if certified** See AMM Task 12-13-11-600-801

Engine Ratings

Maximum Certified Thrust – This is the maximum thrust certified during testing for each series of 737. This is also the thrust that you get when you firewall the thrust levers, regardless of the maximum rated thrust.

On the 737NG, the EEC limits the maximum certified thrust gained from data in the engine strut according to the airplane model as follows:

Aircraft Series Maximum Certified Thrust
737-600 CFM56-7B22 = 22,700lb.st
737-700 CFM56-7B24 = 24,200lb.st
737-800 CFM56-7B27 = 27,300lb.st
737-900 CFM56-7B27 = 27,300lb.st

Maximum Rated Thrust – This is the maximum thrust for the installed engine that the autothrottle will command. This is specified by the operator from the options in the table below.

Engine Aircraft Series Max Static Thrust (lb.st.) Bypass Ratio EGT Margin (C)
JT8D-7/7A/7B 1/200 14,000 1.10
JT8D-9/9A 1/200 14,500 1.04
JT8D-15/15A 200Adv 15,500 0.99
JT8D-17/17A 200Adv 16,000 1.02
JT8D-17R 200Adv 17,400 1.00
CFM56-3B4 500 18,500 5.0 90
CFM56-3B1 3/500 20,000 5.0 70
CFM56-3B2 3/400 22,000 5.0 50
CFM56-3C1 400 23,500 4.9 45
CFM56-7B18 600 19,500 5.5 145
CFM56-7B20 6/700 20,600 5.4 148
CFM56-7B22 6/700 22,700 5.3 150
CFM56-7B24 7/8/900 24,200 5.3 125
CFM56-7B26 7/8/900/BBJ 26,400 5.1 85
CFM56-7B27 8/900/BBJ 27,300 5.0 ?

Misc Photos

The left hand side of the CFM56-3. The large silver coloured pipe is the start air manifold with the starter located at its base. The black unit below that is the CSD. The green unit forward (left) of the CSD is the generator cooling air collector shroud, the silver-gold thing forward of that (with the wire bundle visible) is the generator, and the green cap most forward is the generator cooling air inlet.
The view into the JT8D jetpipe.The corrugated ring is the mixer unit, this is designed to thoroughly mix the bypass air with the turbine exhaust.

The exhaust cone makes a divergent flow which slows down the exhaust and also protects the rear face of the last turbine stage.

The view into the CFM56-3 jetpipe.This is the turbine exhaust area, no mixing is required as the bypass air is exhausted coaxially.
There are two fan inlet temperature sensors in the CFM56-3 engine intake. The one at the 2 o’clock position is used by the PMC and the one at the 11 o’clock position is used by the MEC. The MEC uses the signal to establish parameters to control low and high idle power schedules.The temperature data is used for thrust management and variable bleed valves, variable stator vanes & high / low pressure turbine clearance control systems.
The CFM56-7 inlet has just one fan inlet temperature probe, which is for the EEC (because there is no PMC on the NG’s).A subtle difference between the NG & classic temp probes is that the NG’s only use inlet temp data on the ground and for 5 minutes after take-off. In-flight after 5 minutes temp data is taken from the ADIRU’s.

The temperature data is used for thrust management and variable bleed valves, variable stator vanes & high / low pressure turbine clearance control systems.

The CFM56-7 spinner has a unique conelliptical profile. The first 737-3/400′s had a conical (sharp pointed) spinner but these tended to shed ice into the core. This was one of the reasons for the early limitation of minimum 45% N1 in icing conditions which made descent management quite difficult. They were later replaced with elliptical (round nosed) spinners which succeeded in deflecting the ice away from the core, but because of their larger stagnation point, were more prone to picking up ice in the first place. The conelliptical spinner of the NG’s neatly solves both problems.
The CFM56-7 tailpipe is slightly longer then the CFM56-3 and has a small tube protruding from the faring. This is the Aft Fairing Drain Tube for any hydraulic fluid, oil or fuel that may collect in there. There is also a second drain tube that does not protrude located on the inside of the fairing.
The JT8D tailpipe fitted as standard from l/n 135 onwards.The original thrust reversers were totally redesigned by Boeing and Rohr since the aircraft had inherited the same internal pneumatically powered clamshell thrust reversers as the 727 which were relatively ineffective and apparently tended to lift the aircraft off the runway when deployed! The redesign to external hydraulically powered target reversers cost Boeing $24 million but dramatically improved its short field performance which boosted sales to carriers proposing to use the aircraft as a regional jet from short runways. Also the engine nacelles were extended by 1.14m as a drag reduction measure.
The outboard side of the JT8D-9A with the cowling open.

Emirates chief hits out over A350-1000 revamp

Emirates president Tim Clark has reacted angrily to Airbus‘s plan to revamp the A350-1000.

The airframer revealed a revised specification for its largest A350 variant at the Paris air show, which will result in a two-year delay.

It centres on a modified, more powerful variant of the Trent XWB engine, along with increased weights.

The move sparked an angry response from A350-1000 launch customer Qatar Airways, with chief executive Akbar Al Baker expressing his displeasure during the show.

While Airbus’s official line was the revisions had been introduced to boost payload and range, ­industry sources have speculated there may also have been a need to address weight or performance issues that had emerged with the original design.

Clark said the revisions were implemented without any dialogue: “If they had talked to me, I would have said: ‘[The improvement is] not good enough’,” he added.

Although Emirates has only 20 A350-1000s on order, it had been considering switching its 50 -900 orders to the -1000. However, this is unlikely following the revisions.

“On paper, the old -1000 was hugely economical – it was a 777-300 classic replacement,” Clark said. “That’s why I talked about ­converting my -900 orders.” He added the decision to revamp the A350-1000′s engine by incorporating a new core has had an impact on commonality. “I had 70 aircraft with the same engine. I don’t have that any more,” he said.

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