B737-112 From United States of America, joined Nov 1999, 883 posts, RR: 7 Posted (11 years 12 months 1 day 17 hours ago) and read 2759 times:
I've noticed several times now at BUR that right after the UPS 757 lands and is taxiing back to parking there is an extremely loud sound that lasts a few seconds to a maximum of a minute. It's so loud that it even blocks out all other noises around it, including its own engine whine and other jet departures. The only things I can think of is possibly the APU temporarily being at a much faster RPM (if that's possible) or an oxygen bleed from the aircraft once it's no longer needed. If that's the case why is it only something I hear with the 752?
Rick From United States of America, joined Dec 1999, 129 posts, RR: 0 Reply 1, posted (11 years 12 months 1 day 11 hours ago) and read 2690 times:
There have been numerous post over the last year or so including an origional from me about this noise. I bet you only hear it on the 757's with the PW 2000 engines. Some examples of U.S. airlines that fly the PW2000 are: Delta, United, North West, and the old ex TWA. Some inside people from the airline mechanics industry answered these post but they have since been arcived or deleted. I am not a mechanic, so I will not go into detail, but the noise is the 14th stage airbleed that opens to release air to prevent compressor backfires during rapid deceleration. The air is coming straight out of the core of the engine, so it is very hot and that causes a volitile reaction when it hits the cool outside air. I love the 757, love to fly on it, especially the PW 2000 ones because of that grand finish they make at the end. "And the trombone section stood up!", quote taken from a very good airliners magazine a while ago.