Hi,
Thank you for your post.
Sorry guys but I think I misled you regarding the reliability of the APU's. I didn't mean the reliabilty in general like better mean time between failures or overhaul.... I meant the failures that can occur in flight and cause automatic (protective) shutdown if the APU was operating in flight. For example an old APU (like in 737-200) is protected by 4 automatic shutdowns:low oil pressure, high oil temperature, overspeed, and fire. The APU in the 737- NG is protected by 21 automatic shutdowns, among them: APU inlet overheat, inlet air temperature sensor, loss of both EGT signals,...
So I tought that the recent APU's are more prone (may be) to shutdown while trying to save from probable damage during detected APU malfunctions, because they have more chance to fail: anomaly like inlet air temperature sensor failure or loss of both EGT signals,...etc are not critical or important than high oil tempearture or low oil pressure but yet they can cause automatic shutdown. Such anomalies (like APU inlet overheat, sensors failure,..) can be fixed at the gate or in hangar (does not necessitate the remove of the APU and repair on a shop). So my point it is good to have many automatic shutdowns (protective), but this may affect the utility and the use of the APU if it fails when it was needed.
So now after this long introduction
, do you think that the recent APU's are more prone to AUTOMATIC (PROTECTIVE) SHUTDOWNS in flight than the old APU's?
Feedback appreciated.
Thank you.