Warning Systems – B737

Warning Lights

     

Master Caution and System Annunciator lights, left and right.

 

The Master Caution system was developed for the 737 to ease pilot workload as it was the first Boeing airliner to be produced without a flight engineer. In simple terms it is an attention getter that also directs the pilot toward the problem area concerned. The system annunciators (shown above) are arranged such that the cautions are in the same orientation as the overhead panel e.g. FUEL bottom left, DOORS bottom of third column, etc.

On the ground, the master caution system will also tell you if the condition is dispatchable or if the QRH needs to be actioned. The FCOM gives the following guidance on master caution illuminations on the ground:

Before engine start, use individual system lights to verify the system status. If an individual system light indicates an improper condition:
• check the Dispatch Deviations Procedures Guide (DDPG) or the operator equivalent to decide if the condition has a dispatch effect
• decide if maintenance is needed

If, during or after engine start, a red warning or amber caution light illuminates:
• do the respective non-normal checklist (NNC)
• on the ground, check the DDPG or the operator equivalent

If, during recall, an amber caution illuminates and then extinguishes after a master caution reset:
• check the DDPG or the operator equivalent
• the respective non-normal checklist is not needed

Pressing the system annunciator will show any previously cancelled or single channel cautions. If a single channel caution is encountered, the QRH drill should not be actioned.

Master caution lights and the system annunciator are powered from the battery bus and will illuminate when an amber caution light illuminates. Exceptions to this include a single centre fuel tank LOW PRESSURE light (requires both), REVERSER lights (requires 12 seconds) and INSTR SWITCH (inside normal FoV).

When conducting a light test, during which the system will be inhibited, both bulbs of each caution light should be carefully checked. The caution lights are keyed to prevent them from being replaced incorrectly, but may be interchanged with others of the same caption.

Keying of warning lights

 

  • Red lights – Warning – indicate a critical condition and require immediate action.
  • Amber lights – Caution – require timely corrective action.
  • Blue lights – Advisory – eg valve positions and unless bright blue, ie a valve/switch disagreement, do not require crew action.
  • Green lights – Satisfactory – indicate a satisfactory or ON condition.

 

 

Aural Warnings

Cockpit aural warnings include the fire bell, take-off configuration warning, cabin altitude, landing gear configuration warning, mach/airspeed overspeed, stall warning, GPWS and TCAS. External aural warnings are: The fire bell in the wheel well and the ground call horn in the nose wheel-well for an E & E bay overheat or IRS’s on DC. Only certain warnings can be silenced whilst the condition exists.

To test the GPWS, ensure that the weather radar is on in TEST mode and displayed on the EHSI. Pressing SYS TEST quickly will give a short confidence test, pressing for 10 seconds will give a full vocabulary test.

The GPWS pane. Click photo to hear the GPWS vocabulary test. (175kb)

AURAL WARNING PRIORITY LOGIC
MODE PRIORITY DESCRIPTION ALERT LEVEL
7 1 WINDSHEAR WINDSHEAR WINDSHEAR W
1 2 PULL-UP (SINK RATE) W
2 3 PULL-UP (TERRAIN CLOSURE) W
2A 4 PULL-UP (TERRAIN CLOSURE) W
V1 5 V1 CALLOUT I
TA 6 TERRAIN TERRAIN PULL-UP W
WXR 7 WINDSHEAR AHEAD W
2 8 TERRAIN TERRAIN C
6 9 MINIMUMS I
TA 10 CAUTION TERRAIN C
4 11 TOO LOW TERRAIN C
TCF 12 TOO LOW TERRAIN C
6 13 ALTITUDE CALLOUTS I
4 14 TOO LOW GEAR C
4 15 TOO LOW FLAPS C
1 16 SINK RATE C
3 17 DONT SINK C
5 18 GLIDESLOPE C
WXR 19 MONITOR RADAR DISPLAY C
6 20 APPROACHING MINIMUMS I
6 21 BANK ANGLE C
TCAS 22 RA (CLIMB, DESCEND, ETC.) W
TCAS 23 TA (TRAFFIC, TRAFFIC) C
TEST 24 BITE AND MAINTENANCE INFORMATION I

Radio Altimeter Callouts

Automatic rad-alt calls are a customer option on the 3-900 series. Calls can include any of the following:

2500 (“Twenty Five Hundred” or “Radio Altimeter”).
1000
500
400
300
200
100
50
40
30
20
10

“Minimums” or “Minimums, Minimums”
“Plus Hundred” when 100ft above DH
“Approaching Minimums” when 80ft above DH
“Approaching Decision Height”
“Decision Height”

Customers can also request special heights, such as 60ft.


 

Noise Levels

If is often commented how loud these callouts are. The volume level for these callouts and any other aural warnings is set so that they can still be audible at the highest ambient noise levels, this is considered to be when the aircraft is at Vmo (340kts) at 10,000ft.

The design sound pressure level at 35,000ft, M0.74, cruise thrust is 87dB at the Captains seat, compared to 90-93dB in the cabin.

Many pilots consider the 737 flightdeck to be generally loud. This is Boeings response to that charge:

“Using the flight deck noise levels measured by Boeing Noise Engineering during a typical flight profile (entire flight), a daily A-weighted sound exposure was calculated using ISO/DIS 1999 standards. This calculation indicates the time weight noise exposure is below 80 db(A) and should not cause hearing damage. Flight deck noise improvement continues to be a part of current Boeing product quality improvement activities.”

And when asked later about the particularly noisy NG:

“Boeing has conducted extensive flight tests to define the contributing noise sources for the 737 Flight Deck. Subsequently, various system and hardware modifications have been evaluated for possible improvements. Currently there are no proposed changes where the benefits are significant enough to warrant incorporation. Additional candidates are currently under study and if their merit is validated, they could be incorporated at a later date during production and retrofit.”

That said, in 2005 Boeing added 10 small vortex generators at the base of the windscreen which reduce flightdeck aerodynamic noise by 3dB. (See fuselage page for photo).

 

 

Stall Warning

Stall warning test requires AC power. Also, with no hydraulic pressure, the leading edge flaps may droop enough to cause an asymmetry signal, resulting in a failure of the stall warning system test. If this happens, switch the “B” system electric pump ON to fully retract all flaps and then repeat the test.

System test switches on the aft overhead panel

The 737-1/200’s had a different stall warning panel as shown right:

The OFF light may indicate either a failure of the heater of the angle of attack sensor a system signal failure or a power failure.

The test disc should rotate, indicating electrical continuity, when the switch is held to the test position.

737-200 Stall Warning Panel

 

TCAS

Various versions of TCAS have been fitted to the 737 since its introduction in the 1990’s. The early days of TCAS there were different methods of displaying the visuals. For the Honeywell system (Previously AlliedSignal, previous to that – Bendix/King), their most popular method for non-EFIS airplanes was to install an RA/VSI which was a mechanical VSI that had the “eyebrows” on the outer edge directing the pilot to climb (green) or stay away from (red) and use the separate Radar Indicator for the basic traffic display. Even early EFIS aircraft had the RA/VSI (see photos left & right)

TCAS is now integrated at production into the EFIS displays. The PFD/EADI will display advisories to climb, descend, or stay level since they give the vertical cue to the pilot. The ND/EHSI provides the map view looking down to show targets and their relative altitude and vertical movement relative to your aircraft.

TCAS display integrated onto the ND

 

TCAS control is from the transponder panel.

 

Weather Radar

The beamwidth of the 737 weather radar is 3.5 degrees.

To calculate the height of the cloud tops above your altitude use the following formula:

Cloud tops above a/c (ft) = range (nm) x (tilt – 1.5 deg) x 100

eg Wx at range 40nm stops painting at +2deg tilt. The tops would be 40 x 0.5 x 100 = 2000ft above your level.

Weather radar or terrain can be overlaid onto the EHSI with these switches on the classics. In the NG the overlay switches are part of the EFIS control panel. The colours may appear similar but their meanings are very different.

737 NG’s are fitted with predictive windshear system (PWS). This is available below 2300ft. You do not need weather radar to be switched on for PWS to work, since it switches on automatically when take-off thrust is set. However there is a 12 sec warm up period, so if you want PWS available for the take-off you should switch the weather radar on when you line up.

Windshear warning displayed on the ND. Notice the cone and range at which windshear is predicted.


EGPWS – Peaks Display

The Peaks display overlays EGPWS terrain information onto the EHSI. The colour coding is similar to wx radar but with several densities of each colour being used. The simplified key is:

 

Color Altitude Diff from Aircraft (ft)
Black No terrain
Cyan Zero ft MSL (Customer option)
Green -2000 to +250
Yellow -500 to +2000
Red +2000 or above
Magenta Terrain elevation unknown

The two overlaid numbers are the highest and lowest terrain elevations, in hundreds of ft amsl, currently being displayed. Here 5900ft and 800ft amsl. One of the main difference between Peaks display and others is that it will show terrain more than 2000ft below your level (eg a mountain range from cruise altitude). This can be very useful for situational awareness.

EGPWS Limitations

  • Do not use the terrain display for navigation.
  • Do not use within 15nm of an airfield not in the terrain database.

Honeywell EGPWS Pilots notes

 

PSEUProximity Switch Electronic Unit

The Proximity Switch Electronic Unit (PSEU) is a system that communicates the position or state of system components eg flaps, gear, doors, etc to other systems. The 737-NG’s are fitted with a PSEU which controls the following systems: Take-off and landing configuration warnings, landing gear transfer valve, landing gear position indicating and warning, air/ground relays, airstairs & door warnings and speedbrake deployed warning.

The PSEU light is inhibited from when the thrust levers are set for take-off power (thrust lever angle beyond 53 degrees) until 30 seconds after landing. If the PSEU light illuminates, you have a “non-dispatchable fault” and the QRH says do not take-off. In this condition the PSEU light can only be extinguished by fixing the fault. However if you only get the PSEU light on recall, you have a “dispatchable fault” which it is acceptable to go with. In this condition the PSEU light will extinguish when master caution is reset.

SFP aircraft (-800SFP / -900ER) also have an SPSEU which monitors the 2 position tailskid.

Warning Lights

     

Master Caution and System Annunciator lights, left and right.

The Master Caution system was developed for the 737 to ease pilot workload as it was the first Boeing airliner to be produced without a flight engineer. In simple terms it is an attention getter that also directs the pilot toward the problem area concerned. The system annunciators (shown above) are arranged such that the cautions are in the same orientation as the overhead panel e.g. FUEL bottom left, DOORS bottom of third column, etc.

On the ground, the master caution system will also tell you if the condition is dispatchable or if the QRH needs to be actioned. The FCOM gives the following guidance on master caution illuminations on the ground:

Before engine start, use individual system lights to verify the system status. If an individual system light indicates an improper condition:
• check the Dispatch Deviations Procedures Guide (DDPG) or the operator equivalent to decide if the condition has a dispatch effect
• decide if maintenance is needed

If, during or after engine start, a red warning or amber caution light illuminates:
• do the respective non-normal checklist (NNC)
• on the ground, check the DDPG or the operator equivalent

If, during recall, an amber caution illuminates and then extinguishes after a master caution reset:
• check the DDPG or the operator equivalent
• the respective non-normal checklist is not needed

Pressing the system annunciator will show any previously cancelled or single channel cautions. If a single channel caution is encountered, the QRH drill should not be actioned.

Master caution lights and the system annunciator are powered from the battery bus and will illuminate when an amber caution light illuminates. Exceptions to this include a single centre fuel tank LOW PRESSURE light (requires both), REVERSER lights (requires 12 seconds) and INSTR SWITCH (inside normal FoV).

When conducting a light test, during which the system will be inhibited, both bulbs of each caution light should be carefully checked. The caution lights are keyed to prevent them from being replaced incorrectly, but may be interchanged with others of the same caption.

Keying of warning lights

  • Red lights – Warning – indicate a critical condition and require immediate action.
  • Amber lights – Caution – require timely corrective action.
  • Blue lights – Advisory – eg valve positions and unless bright blue, ie a valve/switch disagreement, do not require crew action.
  • Green lights – Satisfactory – indicate a satisfactory or ON condition.

Aural Warnings

Cockpit aural warnings include the fire bell, take-off configuration warning, cabin altitude, landing gear configuration warning, mach/airspeed overspeed, stall warning, GPWS and TCAS. External aural warnings are: The fire bell in the wheel well and the ground call horn in the nose wheel-well for an E & E bay overheat or IRS’s on DC. Only certain warnings can be silenced whilst the condition exists.

To test the GPWS, ensure that the weather radar is on in TEST mode and displayed on the EHSI. Pressing SYS TEST quickly will give a short confidence test, pressing for 10 seconds will give a full vocabulary test.

The GPWS pane. Click photo to hear the GPWS vocabulary test. (175kb)

AURAL WARNING PRIORITY LOGIC
MODE PRIORITY DESCRIPTION ALERT LEVEL
7 1 WINDSHEAR WINDSHEAR WINDSHEAR W
1 2 PULL-UP (SINK RATE) W
2 3 PULL-UP (TERRAIN CLOSURE) W
2A 4 PULL-UP (TERRAIN CLOSURE) W
V1 5 V1 CALLOUT I
TA 6 TERRAIN TERRAIN PULL-UP W
WXR 7 WINDSHEAR AHEAD W
2 8 TERRAIN TERRAIN C
6 9 MINIMUMS I
TA 10 CAUTION TERRAIN C
4 11 TOO LOW TERRAIN C
TCF 12 TOO LOW TERRAIN C
6 13 ALTITUDE CALLOUTS I
4 14 TOO LOW GEAR C
4 15 TOO LOW FLAPS C
1 16 SINK RATE C
3 17 DONT SINK C
5 18 GLIDESLOPE C
WXR 19 MONITOR RADAR DISPLAY C
6 20 APPROACHING MINIMUMS I
6 21 BANK ANGLE C
TCAS 22 RA (CLIMB, DESCEND, ETC.) W
TCAS 23 TA (TRAFFIC, TRAFFIC) C
TEST 24 BITE AND MAINTENANCE INFORMATION I

Radio Altimeter Callouts

Automatic rad-alt calls are a customer option on the 3-900 series. Calls can include any of the following:

2500 (“Twenty Five Hundred” or “Radio Altimeter”).
1000
500
400
300
200
100
50
40
30
20
10

“Minimums” or “Minimums, Minimums”
“Plus Hundred” when 100ft above DH
“Approaching Minimums” when 80ft above DH
“Approaching Decision Height”
“Decision Height”

Customers can also request special heights, such as 60ft.


Noise Levels

If is often commented how loud these callouts are. The volume level for these callouts and any other aural warnings is set so that they can still be audible at the highest ambient noise levels, this is considered to be when the aircraft is at Vmo (340kts) at 10,000ft.

The design sound pressure level at 35,000ft, M0.74, cruise thrust is 87dB at the Captains seat, compared to 90-93dB in the cabin.

Many pilots consider the 737 flightdeck to be generally loud. This is Boeings response to that charge:

“Using the flight deck noise levels measured by Boeing Noise Engineering during a typical flight profile (entire flight), a daily A-weighted sound exposure was calculated using ISO/DIS 1999 standards. This calculation indicates the time weight noise exposure is below 80 db(A) and should not cause hearing damage. Flight deck noise improvement continues to be a part of current Boeing product quality improvement activities.”

And when asked later about the particularly noisy NG:

“Boeing has conducted extensive flight tests to define the contributing noise sources for the 737 Flight Deck. Subsequently, various system and hardware modifications have been evaluated for possible improvements. Currently there are no proposed changes where the benefits are significant enough to warrant incorporation. Additional candidates are currently under study and if their merit is validated, they could be incorporated at a later date during production and retrofit.”

That said, in 2005 Boeing added 10 small vortex generators at the base of the windscreen which reduce flightdeck aerodynamic noise by 3dB. (See fuselage page for photo).

Stall Warning

Stall warning test requires AC power. Also, with no hydraulic pressure, the leading edge flaps may droop enough to cause an asymmetry signal, resulting in a failure of the stall warning system test. If this happens, switch the “B” system electric pump ON to fully retract all flaps and then repeat the test.

System test switches on the aft overhead panel

The 737-1/200’s had a different stall warning panel as shown right:

The OFF light may indicate either a failure of the heater of the angle of attack sensor a system signal failure or a power failure.

The test disc should rotate, indicating electrical continuity, when the switch is held to the test position.

737-200 Stall Warning Panel

TCAS

Various versions of TCAS have been fitted to the 737 since its introduction in the 1990’s. The early days of TCAS there were different methods of displaying the visuals. For the Honeywell system (Previously AlliedSignal, previous to that – Bendix/King), their most popular method for non-EFIS airplanes was to install an RA/VSI which was a mechanical VSI that had the “eyebrows” on the outer edge directing the pilot to climb (green) or stay away from (red) and use the separate Radar Indicator for the basic traffic display. Even early EFIS aircraft had the RA/VSI (see photos left & right)

TCAS is now integrated at production into the EFIS displays. The PFD/EADI will display advisories to climb, descend, or stay level since they give the vertical cue to the pilot. The ND/EHSI provides the map view looking down to show targets and their relative altitude and vertical movement relative to your aircraft.

TCAS display integrated onto the ND

 

TCAS control is from the transponder panel.

Weather Radar

The beamwidth of the 737 weather radar is 3.5 degrees.

To calculate the height of the cloud tops above your altitude use the following formula:

Cloud tops above a/c (ft) = range (nm) x (tilt – 1.5 deg) x 100

eg Wx at range 40nm stops painting at +2deg tilt. The tops would be 40 x 0.5 x 100 = 2000ft above your level.

Weather radar or terrain can be overlaid onto the EHSI with these switches on the classics. In the NG the overlay switches are part of the EFIS control panel. The colours may appear similar but their meanings are very different.

737 NG’s are fitted with predictive windshear system (PWS). This is available below 2300ft. You do not need weather radar to be switched on for PWS to work, since it switches on automatically when take-off thrust is set. However there is a 12 sec warm up period, so if you want PWS available for the take-off you should switch the weather radar on when you line up.

Windshear warning displayed on the ND. Notice the cone and range at which windshear is predicted.


EGPWS – Peaks Display

The Peaks display overlays EGPWS terrain information onto the EHSI. The colour coding is similar to wx radar but with several densities of each colour being used. The simplified key is:

Color Altitude Diff from Aircraft (ft)
Black No terrain
Cyan Zero ft MSL (Customer option)
Green -2000 to +250
Yellow -500 to +2000
Red +2000 or above
Magenta Terrain elevation unknown

The two overlaid numbers are the highest and lowest terrain elevations, in hundreds of ft amsl, currently being displayed. Here 5900ft and 800ft amsl. One of the main difference between Peaks display and others is that it will show terrain more than 2000ft below your level (eg a mountain range from cruise altitude). This can be very useful for situational awareness.

EGPWS Limitations

  • Do not use the terrain display for navigation.
  • Do not use within 15nm of an airfield not in the terrain database.

Honeywell EGPWS Pilots notes

PSEUProximity Switch Electronic Unit

The Proximity Switch Electronic Unit (PSEU) is a system that communicates the position or state of system components eg flaps, gear, doors, etc to other systems. The 737-NG’s are fitted with a PSEU which controls the following systems: Take-off and landing configuration warnings, landing gear transfer valve, landing gear position indicating and warning, air/ground relays, airstairs & door warnings and speedbrake deployed warning.

The PSEU light is inhibited from when the thrust levers are set for take-off power (thrust lever angle beyond 53 degrees) until 30 seconds after landing. If the PSEU light illuminates, you have a “non-dispatchable fault” and the QRH says do not take-off. In this condition the PSEU light can only be extinguished by fixing the fault. However if you only get the PSEU light on recall, you have a “dispatchable fault” which it is acceptable to go with. In this condition the PSEU light will extinguish when master caution is reset.

SFP aircraft (-800SFP / -900ER) also have an SPSEU which monitors the 2 position tailskid.

Lights, Water System, Airstairs, Door, Tip clearances, Cargo Holds – B737

Lights

From L to R along the panel:

O/B Landing: (Not NG) Three position switch Off – Extend (off) – On. These are located on the outboard flap faring.

Retractable Landing: (NG only) Replaces the outboard landing lights on the earlier series. These are located on the fuselage just beneath the ram air intakes. The word is that they may be being moved back to their original position on the flap track faring due to excessive stone damage.

Note Use of both of these lights should be avoided at speeds above 250kts due to excessive air loads on their hinges.

Retractable landing light – NG

I/B Landing: Known as fixed landing lights on the NG. Are located in the wing roots, usually used for all day and night landings for conspicuity.

R/W Turnoff: Also in the wing roots, normally only used at night on poorly lit runways.

Taxi: This 250W light is located on the nose gear, on later models it will switch off automatically with gear retraction. It is common practice to have this on whilst the aircraft is in motion as a warning to other aircraft and vehicles.

Logo: Are on each wingtip or horizontal stabiliser and illuminate the fin. Apart from the advertising value on the ground, they are often used for conspicuity in busy airspace.

Position: Depending upon customer option this can be a three position switch (as illustrated) to combine the strobe. Strobe & Steady / Off / Steady, where steady denotes the red, green & white navigation lights. The three Nav lights are no-go items at night.

Strobe: (Not illustrated) Off / Auto / On. Auto is activated by a squat switch. They are also in the wing tips and are very brilliant. This gives rise to great debate amongst pilots about when exactly they should be switched on as they can dazzle other pilots nearby. many people choose to put them on as they enter an active runway for conspicuity against landing traffic.

Anti-Collision: Are the orange rotating beacons above and below the fuselage. They are universally used as a signal that the engines are running or are about to be started. They are typically not switched off until N1 has reduced to below 3.5% (or N2 below 20%) when it is considered safe for ground personnel to approach the aircraft.

Wing: These are mounted in the fuselage and shine down the leading edge of the wing for ice or damage inspection at night.

Wheel Well: Illuminates the main and nose wheel wells. Normally only used during the turnaround at night for the pre-flight inspection but must also be on to see through the gear downlock viewers at night, hence they are a no-go item at night in all but the NG’s. There is also a switch for the main wheel well light in the port wheel well.

Water System

There is a 30 US Gal tank (40 US Gal –400 series) behind the aft cargo hold for potable water. This serves the galleys and washbasins, but not the toilets as they use chemicals. Waste water is either drained into the toilet tanks or expelled through heated drain masts.

The tank indicator (-3/4/500 version shown left) is located over the rear service door. Press to test, indications are clockwise from 7 O’clock: Empty, 1/4, 1/2, 3/4, Full. The NG has an LED panel that is always lit (below) for both potable water and waste tank.

Potable Water Quantity Indicator – NG

Potable Water Quantity Indicator – Classics

Airstairs

Forward Airstairs

May be operated from either internal or external panels. The internal panel requires the forward entry door to be at least partially open. Both panels have normal and standby systems. Normal requires AC and DC power, standby only requires DC. External standby system power comes from the battery bus and so does not require the battery switch to be on.

On classics, if the airstairs will not operate, check the striker pin (see photo below) at the bottom left of the door frame. Move it about and ensure it is vertical, this will often cure the problem. They have a tendency to freeze in position on long flights were the doors have got wet.

Caution: The handrails must be stowed before retraction. The use of standby system from either panel will bypass the handrail and lower-ladder safety circuits. Note that the NG has an red covered EMERG switch underneath the airstairs for emergency retraction, this also bypasses any safety circuits.

Maximum wind speed for airstair operation: 40kts.

Maximum wind speed for airstair extended: 60kts.

Airstairs should not be operated more frequently than 3 consecutive cycles of normal system operation within a 20 minute period.

Note that there have been at least 4 cases of children falling through the gaps in the rails of the airstairs FAA SAIB refers.

Aft Airstairs

In the drive for self sufficiency, these were fitted to about 120 737-200’s. They were much more complicated than forward airstairs as they folded in two places and took the door downwards with them. If you have ever considered the forward airstairs to be temperamental then you would not get on with aft airstairs.

There were several reports of inadvertent deployment and even two instances of them extending after take-off. Boeing say that after one of the in-flight deployments the crew landed with little control problem and apart from some scuff marks on the foot plates where they made contact with the runway, they were still in working order after the event!

              

737-3/4/500 Door showing latch fitting (above), striker pin (below) and 3 stop pin fittings

Underneath NG Airstairs – Notice the red guarded MAINT switch.

Doors

Amber light will illuminate with Master Caution “DOORS” when a door is unlocked. Air Stair must be fully stowed, even if fwd entry door is closed. Equip is for E & E bay and Radar bay.

The sequence of door lights is changed in the NG’s to accommodate the left and right overwing annunciators. They are located between the fwd & aft entry/service door lights.

On the NG, it is not uncommon to get an overwing caption illuminate for a fraction of a second as you start the take-off run. This is due to the overwing exit automatic locking function being slightly slow.

Maximum wind speed for door operation: 40kts.

The doors may remain latched open in winds of up to: 65Kts.

(AMM 52-10-00-011 Rev 0 09)

200C door panel

Classic door panel

NG door panel

Nose, wing tip & tail clearance

The following table shows the increased radius of turn of the wing and tail relative to the nose during a turn with full nose wheel steering applied. This table shows that turning in a 737-600 is probably most hazardous because the wings and tail turn out much further than the nose.

Radius of turn (ft)
Series Nose Wing Tail
-300 55 +5 + 9
-400 61 +1 + 7
-500 50 +9 +10
-600 51 +17 +11
-700 56 +13 +10
-800 66 +6 +9
-900 71 +2 +7

Cargo Holds

Both cargo holds are designed to confine a fire without endangering the safety of the aircraft. A cargo fire detection and extinguishing system may be fitted as an option (see Fire Protection). NB If a hold ceiling light lens cover is broken or missing this is a fire hazard and the bulb should be removed if the cover can not be fixed.

Cargo-Compartment Class
Model Lower cargo compartment Main cargo compartment
737-100/-200/-300/-400/-500 (line no. 1-3078 Class D Not required
737-300/-400/-500 (line no. 3079 and higher) Class C Not required
737-600/-700/-800 (line no. 1-90) Class D Not required
737-600/-700/-800 (line no. 91 and higher) Class C Not required
737-C/QC Class D Class E

Class C: Compartments that contain both the smoke-detection and fire-suppression of a minimum initial concentration of 5 percent Halon throughout the compartment to suppress any combustion to controllable levels. Thereafter, the system must sustain a minimum concentration of 3 percent Halon for 60 min to prevent reignition or spreading of the combustion.

Class D: Compartments that depend on oxygen deprivation to prevent and suppress combustion.

Class E: Compartments that have a smoke-detection system alert the flight crew within 60 sec from the time smoke first appears in the compartment.

The holds are sealed and pressurised but have no fresh air circulation. They have no temperature control but are heated by exhausting cabin air around their walls. The forward hold also has additional heating from E & E bay air. Live cargo can be carried on either cargo compartment but the forward hold is preferred.

Lights

From L to R along the panel:

O/B Landing: (Not NG) Three position switch Off – Extend (off) – On. These are located on the outboard flap faring.

Retractable Landing: (NG only) Replaces the outboard landing lights on the earlier series. These are located on the fuselage just beneath the ram air intakes. The word is that they may be being moved back to their original position on the flap track faring due to excessive stone damage.

Note Use of both of these lights should be avoided at speeds above 250kts due to excessive air loads on their hinges.

Retractable landing light – NG

I/B Landing: Known as fixed landing lights on the NG. Are located in the wing roots, usually used for all day and night landings for conspicuity.

R/W Turnoff: Also in the wing roots, normally only used at night on poorly lit runways.

Taxi: This 250W light is located on the nose gear, on later models it will switch off automatically with gear retraction. It is common practice to have this on whilst the aircraft is in motion as a warning to other aircraft and vehicles.

Logo: Are on each wingtip or horizontal stabiliser and illuminate the fin. Apart from the advertising value on the ground, they are often used for conspicuity in busy airspace.

Position: Depending upon customer option this can be a three position switch (as illustrated) to combine the strobe. Strobe & Steady / Off / Steady, where steady denotes the red, green & white navigation lights. The three Nav lights are no-go items at night.

Strobe: (Not illustrated) Off / Auto / On. Auto is activated by a squat switch. They are also in the wing tips and are very brilliant. This gives rise to great debate amongst pilots about when exactly they should be switched on as they can dazzle other pilots nearby. many people choose to put them on as they enter an active runway for conspicuity against landing traffic.

Anti-Collision: Are the orange rotating beacons above and below the fuselage. They are universally used as a signal that the engines are running or are about to be started. They are typically not switched off until N1 has reduced to below 3.5% (or N2 below 20%) when it is considered safe for ground personnel to approach the aircraft.

Wing: These are mounted in the fuselage and shine down the leading edge of the wing for ice or damage inspection at night.

Wheel Well: Illuminates the main and nose wheel wells. Normally only used during the turnaround at night for the pre-flight inspection but must also be on to see through the gear downlock viewers at night, hence they are a no-go item at night in all but the NG’s. There is also a switch for the main wheel well light in the port wheel well.

Water System

There is a 30 US Gal tank (40 US Gal –400 series) behind the aft cargo hold for potable water. This serves the galleys and washbasins, but not the toilets as they use chemicals. Waste water is either drained into the toilet tanks or expelled through heated drain masts.

The tank indicator (-3/4/500 version shown left) is located over the rear service door. Press to test, indications are clockwise from 7 O’clock: Empty, 1/4, 1/2, 3/4, Full. The NG has an LED panel that is always lit (below) for both potable water and waste tank.

Potable Water Quantity Indicator – NG

Potable Water Quantity Indicator – Classics

Airstairs

Forward AirstairsMay be operated from either internal or external panels. The internal panel requires the forward entry door to be at least partially open. Both panels have normal and standby systems. Normal requires AC and DC power, standby only requires DC. External standby system power comes from the battery bus and so does not require the battery switch to be on.

On classics, if the airstairs will not operate, check the striker pin (see photo below) at the bottom left of the door frame. Move it about and ensure it is vertical, this will often cure the problem. They have a tendency to freeze in position on long flights were the doors have got wet.

Caution: The handrails must be stowed before retraction. The use of standby system from either panel will bypass the handrail and lower-ladder safety circuits. Note that the NG has an red covered EMERG switch underneath the airstairs for emergency retraction, this also bypasses any safety circuits.

Maximum wind speed for airstair operation: 40kts.

Maximum wind speed for airstair extended: 60kts.

Airstairs should not be operated more frequently than 3 consecutive cycles of normal system operation within a 20 minute period.

Note that there have been at least 4 cases of children falling through the gaps in the rails of the airstairs FAA SAIB refers.

Aft Airstairs

In the drive for self sufficiency, these were fitted to about 120 737-200’s. They were much more complicated than forward airstairs as they folded in two places and took the door downwards with them. If you have ever considered the forward airstairs to be temperamental then you would not get on with aft airstairs.

There were several reports of inadvertent deployment and even two instances of them extending after take-off. Boeing say that after one of the in-flight deployments the crew landed with little control problem and apart from some scuff marks on the foot plates where they made contact with the runway, they were still in working order after the event!

               737-3/4/500 Door showing latch fitting (above), striker pin (below) and 3 stop pin fittings

Underneath NG Airstairs – Notice the red guarded MAINT switch.

Doors

Amber light will illuminate with Master Caution “DOORS” when a door is unlocked. Air Stair must be fully stowed, even if fwd entry door is closed. Equip is for E & E bay and Radar bay.

The sequence of door lights is changed in the NG’s to accommodate the left and right overwing annunciators. They are located between the fwd & aft entry/service door lights.

On the NG, it is not uncommon to get an overwing caption illuminate for a fraction of a second as you start the take-off run. This is due to the overwing exit automatic locking function being slightly slow.

Maximum wind speed for door operation: 40kts.

The doors may remain latched open in winds of up to: 65Kts.

(AMM 52-10-00-011 Rev 0 09)

200C door panel

Classic door panel

NG door panel

Nose, wing tip & tail clearance

The following table shows the increased radius of turn of the wing and tail relative to the nose during a turn with full nose wheel steering applied. This table shows that turning in a 737-600 is probably most hazardous because the wings and tail turn out much further than the nose.

Radius of turn (ft)
Series Nose Wing Tail
-300 55 +5 + 9
-400 61 +1 + 7
-500 50 +9 +10
-600 51 +17 +11
-700 56 +13 +10
-800 66 +6 +9
-900 71 +2 +7

Cargo Holds

Both cargo holds are designed to confine a fire without endangering the safety of the aircraft. A cargo fire detection and extinguishing system may be fitted as an option (see Fire Protection). NB If a hold ceiling light lens cover is broken or missing this is a fire hazard and the bulb should be removed if the cover can not be fixed.

Cargo-Compartment Class
Model Lower cargo compartment Main cargo compartment
737-100/-200/-300/-400/-500 (line no. 1-3078 Class D Not required
737-300/-400/-500 (line no. 3079 and higher) Class C Not required
737-600/-700/-800 (line no. 1-90) Class D Not required
737-600/-700/-800 (line no. 91 and higher) Class C Not required
737-C/QC Class D Class E

Class C: Compartments that contain both the smoke-detection and fire-suppression of a minimum initial concentration of 5 percent Halon throughout the compartment to suppress any combustion to controllable levels. Thereafter, the system must sustain a minimum concentration of 3 percent Halon for 60 min to prevent reignition or spreading of the combustion.

Class D: Compartments that depend on oxygen deprivation to prevent and suppress combustion.

Class E: Compartments that have a smoke-detection system alert the flight crew within 60 sec from the time smoke first appears in the compartment.

The holds are sealed and pressurised but have no fresh air circulation. They have no temperature control but are heated by exhausting cabin air around their walls. The forward hold also has additional heating from E & E bay air. Live cargo can be carried on either cargo compartment but the forward hold is preferred.