DC 10-10 Engine Noise

[Jeffrey S]

Hello again all.

I am a trainee Pilot, studying to from zero to atpl.

I was on the MyTravel MD DC10-10 this march to MBJ. i spoke to the captain after landing, and we spoke about general stuff, eg how he approached runway using VOR-DME ect and how he had over 12,000 hours. (nice man!) but what i forgot to ask him, is what i would like to trouble you with:

what on earth is that strange hissing noise coming from the engine (sounds like steam or something, but is not) especially when taxying or approaching.

does anyone know?


rgards,


Jeffrey.

[Volume]

On some engines air is bled from some stages of the compressor during acceleration to avoid compressor stalls. This might have been the hissing sound.

[Jeffrey S]

Oh right.

It was more of a whoosh! followed by a hum. My fault.

[747FOCAL]

I think you are hearing the ADP Air Driven Pump. In normal mode they are switched to auto so they "pop" on and off. They are quite loud and do effect approach noise levels on some aircraft.