B737 single pack high flow rate

[Banana Joe]

I have a small uncertainty about the single pack ops to high air flow. The FCOM says that with one pack not operating, the other pack will automatically switch to high air flow in flight with flaps up, while the QRH, i.e. engine failure or shutdown, requires to move the affected side pack switch to off to regulate the remaining pack to high air flow.

Of course, I would always follow the QRH, but I really want to be sure about the working of the system and if also the FCOM actually requires to move the inop pack switch to OFF. English isn't my first language and the word "automatically" might lead me to believe something not correct.

[BAengineer]

In the air, if the opposite pack control valve is closed the remaining pack goes to high flow.

In the air or on the ground, if the opposite engine bleed is selected off the onside pack goes to high flow.

Hope that is clear

[sonicbum]

I have a small uncertainty about the single pack ops to high air flow. The FCOM says that with one pack not operating, the other pack will automatically switch to high air flow in flight with flaps up, while the QRH, i.e. engine failure or shutdown, requires to move the affected side pack switch to off to regulate the remaining pack to high air flow.

Of course, I would always follow the QRH, but I really want to be sure about the working of the system and if also the FCOM actually requires to move the inop pack switch to OFF. English isn't my first language and the word "automatically" might lead me to believe something not correct.

Hi,

In case of an engine failure the associated pack is operating, it is just not supplied with bleed air as the engine has been shutdown. Hence the QRH directs You to switch if off. On the other hand if You do have a specific pack issue the pack will trip off and prompt the other pack to supply high flow (flaps up) till You try to reset the trip off. If You are successful You go back to 2 packs operation in normal flow otherwise You will switch the affected pack off and the remaining will operate in high flow.

[Banana Joe]

Ok now it's clear. Thanks!