Boeing 757 flap screeching sound (?)
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Joined: Apr 2006
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From: Finland
Boeing 757 flap screeching sound (?)
Hello, What causes this very distinct screeching sound inside the Boeing 757 cabin, which can be heard when the flaps are operated? I used to think it was the ADP "screaming" under the belly of the airplane, but I just noticed that the 757 doesn't have an ADP (by watching pictures of the 757 overhead panel). Seems to me that there are only engine driven pumps and electric pumps, correct? Do they cause the sound? Thanks in advance
Gender Faculty Specialist
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From: In your head.
I would assume it's the airflow 'whistling' through the slots on the fowler flaps. It's also noticeable on the 146. And I believe it's called "fluting".
I stand to be corrected!
CM
I stand to be corrected!
CM
Thread Starter
Joined: Apr 2006
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From: Finland
You can hear this noice on ground as well as in flight, whenever the flaps are in motion. Isn't the Power Transfer Unit (PTU) for backup only and not operating in normal conditions? Would anyone know about the electric pumps - are they loud?
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From: In your head.
I know some aeroplanes where the PTU runs when you select flaps up or down. As Golden Rivet said, it is most likely this. Unless the flap jacks need greasing!!
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The noise is the PDUs (forward and aft power drive units ) operating and turning the torque bars, which transfer power to the flap gearboxes on the wing. The aft PDU and torque bar is the noisiest. The aft PDU drives the trailing edge flaps and the fwd PDU drives the leading edge flaps.
Joined: Jun 2005
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From: in denial
Same thing occurs on the 767.
It only happens though when selecting "Flap 1", which is leading edge motion only, so I presume then that this would be the forward PDU in operation. The noise is quite noticeable on the flightdeck.
The noise can be heard on the ground also. Can always tell when a 767 flying overhead selects the first stage of flap; it emits this strange "uuurrrrt" kind of sound
It only happens though when selecting "Flap 1", which is leading edge motion only, so I presume then that this would be the forward PDU in operation. The noise is quite noticeable on the flightdeck.
The noise can be heard on the ground also. Can always tell when a 767 flying overhead selects the first stage of flap; it emits this strange "uuurrrrt" kind of sound
Joined: Jul 2005
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From: n/a
Hey Veruka!!!
Your not refering to the 767-300 that accidently had some 200 leading edge flaps wedged on during heavy maintenance???
Took a long time to work out what the srceech was with selecting flap during approach..........
Your not refering to the 767-300 that accidently had some 200 leading edge flaps wedged on during heavy maintenance???
Took a long time to work out what the srceech was with selecting flap during approach..........
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From: Mumbai, INDIA
PTU is only used if LH EDP pr is low or LH Eng RPM reduces below a certain level.
Its not normally operated.
PTU pump is driven by RH Hyd system thru a PTU Motor that drives the PTU pump to supply LH Hyd fluid.
The Noise is Probably the Flap PDUs & Slat PDUs.
regds
MEL
Its not normally operated.
PTU pump is driven by RH Hyd system thru a PTU Motor that drives the PTU pump to supply LH Hyd fluid.
The Noise is Probably the Flap PDUs & Slat PDUs.
regds
MEL
