Originally Posted by
hkfree
there is engine manufacturer guideline for warm up time required before TO thrust is set, which can be done before performance RETO.
Generally 3 minutes from a 'cold' start to TO (at least on the engine types I'm familiar with).
However, if the engine is truly 'cold' (i.e. shutdown for several hours), 3 minutes is pretty sporty. Especially on 'fresh' engines, 3 minutes from cold can still result in seal rubs and
permanent loss of performance. If it's a quick turn-around (less than an hour), 3 minutes is fine, but
not after an overnight. Of course, once an engine has a few thousand hours on it, seals and such have already been worn and this is less of a concern.
When we did high power engine runs at Boeing, it was always a minimum of 5 minutes from start to setting climb power or above.