The Boeing Template for 737NG FCOM in
all procedures published (except those referencing specifically different) makes the following assumption: APU is used for air-conditioning.
The above assumption is usually
NOT used by airlines in more recent times due fuel saving practices and noise restrictions at airports, therefore the placements of switches to facilitate this should be addressed when these procedures are implemented.
Therefore the template document makes the following collection of statements about NG Series aircraft in the pre-flight
Air conditioning panel.............. Set:
AIR TEMPERATURE source selector - As needed
[737-800/900] TRIM AIR switch - ON
[737-600/700] Verify the DUCT OVERHEAT lights are extinguished
[737-800/900] Verify the ZONE TEMP lights are extinguished
Temperature selectors - As needed
Verify that the RAM DOOR FULL OPEN lights are illuminated
[737-600/700] RECIRCULATION FAN switch - AUTO
[737-800/900] RECIRCULATION FAN switches - AUTO
Air conditioning PACK switches - AUTO or HIGH
ISOLATION VALVE switch - OPEN
Engine BLEED air switches - ON
APU BLEED air switch - ON
Verify that the DUAL BLEED light is illuminated
[737-600/700] Verify that the PACK TRIP OFF lights are extinguished
[737-800/900] Verify that the PACK lights are extinguished
Verify that the WING-BODY OVERHEAT lights are extinguished
Verify that the BLEED TRIP OFF lights are extinguished
All steps below the statement
APU BLEED air switch - ON require you to have an air source available to complete the annunciation checks of the described lights.
Therefore, the steps immediately prior to this facilitate what you are trying to achieve and by opening the isolation valve both sides of the duct are pressurised and thus the checklist can be continued to checked for accurate indications.
IF your company or airport thus does not (allow/prefer) to use the APU during this stage of flight
or if the APU is INOP, the statements following describing the indications of lights cannot be checked and these checks should be introduced/moved at that point in the checklist flow where such checks can be performed. Two possibilities of which the second requires NO modification of the FCOM:
- Immediately prior to the Engine Start Procedure when an External Air Cart or APU (therefore duct pressure) is available [thus having to physically move the check items in the checklist];
- Inclusion of the check items in the Before Taxi Procedure.
* Setting up the panel for a pressurised takeoff at step Recall.......Check states: Verify that all system annunciator panel lights illuminate and then extinguish.
Note: standard Boeing also have the F/O or RHS start engines at all times, and assign designated areas of responsibility C and F/O or LHS/RHS for the Before Taxi Procedure, not PF/PNF, again this may be different in a variation of your company's FCOM...