Originally Posted by
B2N2
So the book says “START”.
Insight and technical understanding would warrant a particular technique....
So we just go braindead and turn the switch regardless of conditions or do we apply a light coating of mechanical empathy?
you assume the need for a technique without considering that perhaps there has been an analysis conducted by a team of professional engineers in an office working for the apu oem, the aircraft manufacturer and the airline whose sole job description might be to consider the effects of temperature on apu/jet engine performance, BEFORE apu certification and IN-SERVICE, on a worldwide fleet, with experience in a range of operating conditions.
An assumption is also made that somehow all pilots around the world have been applying the suggested ‘technique’, leading to the apu reliability rates that underpin etops certification.
No - I just don’t think so. I think pilots have been cranking straight away relying on inbuilt protections (as designed and certified) to auto-shutdown if the apu is unhappy.
There is nothing wrong with developing technique, but some measure of reason needs to be applied and tested, and I don’t think delaying an apu start for cold soaked apu because it is thought to be healthy for it, is reasonable. There is no evidence that supports the technique unlike the other examples you gave, which can be sensed immediately and reacted to.
all that said, I think the suggested technique is one of little risk with fod ingestion being the biggest issue but even then, apu’s generally have a screen that captures the crap.