Engine cool time

[steelbird]

The 737 CFM engines have a 3 minute cool time before shutdown with a provision for 1 minute cooling time for operational reasons.
Is schedule a valid "operational " reason to shutdown after a minute ? I think not, as why else would there be a recommendation to wait 3 min before s/down ?I believe the 1 minute provision is for exigencies not schedule.
What do you think?
:confused:

[gas path]

Probably what is meant is that in an ideal world 3 mins. is required before shutdown, but for operational reasons eg. small airfields with minimal taxi time from runway to ramp then 1 min. is acceptable.
The cooldown time is there to allow the engine spools and casings temperatures to equalise.
FWIW the GE90 requires 10 mins. which is difficult to achieve at some fields.
The most noticeable effect of shutting down from a high power setting without allowing the core to cool is seized rotors (the good old P and W JT9D was good for that) to high vibration on start up (Typical of GE CF6 and GE90 (bowed rotor))

[Max Angle]

V2500's on our Airbus's are supposed to have 5 mins at idle before take-off if they have been shutdown for 2 hours or more and 3 minutes idle before shutdown. Needs some slow taxi speeds sometimes to avoid runnning on the stand for a few minutes.

[Al Weaver]

Temp control before takeoff is often related to the thermal stress distribution in the rotor parts and the fatigue life of these parts. Not to say that under rarer circumstances taxi out temp control might be related to gas path clearances as well.

[spannerhead]

Maybe slightly off he subject but you may (or may not) be interested to know that even after a cfm 56 has been shut down for a few hours, it is very difficult to turn via the gearbox turning point. We use this procedure during borescope inspections.
The heat soak goes to the top of the engine causing the hp rotor to slightly bow. You would not believe the difference between a hot engine and a cold one.
Also, you may be interested to know that after an engine change we carry out a timed accel check of the engine. This check we carry out last. The difference between an engine that has been sat at idle for 10 minutes and an engine that has been at high power for 10 minutes can be a much as 2 seconds from flight idle to T/O power. 2 seconds is a lot of time during a go around.