In the front preamble section of the (
Boeing) QRH(s) - i.e. about how to use that hallowed tome ('
Non–Normal Checklist Use') - it says:
The pilot flying calls for the checklist when:
- the flight path is in control.
- the airplane is not in a critical phase of flight (such as takeoff or landing).
- all recall items are complete
That said, the QRH of my B767-300ER tells me that in the event of an 'Engine Overheat' one of the first things one must do is to turn off the engine bleed air on the effected side... However it makes no mention of the fact that doing this above FL350 (
which is the limit for operations on a single pack / bleed source - as per the DDPM for this type) might lead one into a cabin decompression, i.e. whilst one gently drifts down to a lower level on 1-and-a-bit engines ?! Therein
the QRH is not infallible and it's been said that there's many a pilot who's died whilst holding the QRH their hand!