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:
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
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.
2500 ("Twenty Five Hundred" or "Radio Altimeter").
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).
System test switches on the aft overhead panel
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.
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.|
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.
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.