Strange noise on 757:

Landing gear...?

 

If there was a problem, most likely there would be an EICAS message or STATUS message for the pilots. Unless your an A&P trained in type or a pilot trained in type more than likely it would get blown off. We get all sorts of calls from F/A about "strange noises"

More than likely what you were hearing is the Slat PDU which is in the left wing root.
The flap PDU is in the left wheel well. PDU is power drive unit which gets its signal from the flap lever.

Cheers

 

I'll just mention what I know as a point from which to start. The flaps and slats on all the Boeing jets on which I have worked are driven by hydraulic motors ( if my old head remembers rightly) that rotate a single torque tube continuous from wing tip to wing tip. The torque tube drives retraction and extension shafts by means of a series of gear boxes that make a lot of whirring noises. One can hear the TE flap drive if he sits near the rear spar on outside row seats. The 747 has air driven slats that make a huge howl when they are operating.
Early in the 707 program the main landing gear doors made a loud rumble that was never heard on the prop planes since the LG was out in the nacelles. The company was worried that the new jet passengers would be startled and frightened by the noise and they launched a design effort to put baffles slaved to the MG operation on the forward edge of the wheelwell but after many tests the "Rube Goldberg" machinery was abandoned . There were complaints at times but a simple explanation sufficed. Millions were wasted on that effort.
Switches

 

They also work electrically in the alternate mode in the 757/767. The gearbox you refer to is called the PDU. In the electric mode it takes more than 2 minutes to deploy to flaps 20. I just did a Functional Flight Test out of GYR today in a 757 and they did just that! Great system and backup.

Cheers

 

I've experienced the same thing, and as they come in all shapes and sizes, attributed it to Gremlins.
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I will talk to the Gremlin Guru in my old group today about gremlinoise. The slats are mechanically held in place after retracting. I suspect some other machinery running.

 

I would guess either a gear door seal or a wing-root fairing seal. Maybe when the slats were retracted it changed the airflow just enough to get a small piece of exposed rubber to start vibrating. They can make quite a lot of noise. Afterwards they usually leave black rub marks that are visible on pre-flight. The quick fix...Metallic speed tape.

Dave

 

Hey, you posted that before I got a chance to! I'm quite sure I thought of it first though...

 

I used to work on these at the delivery center and Renton Flight Line and what I would think you heard was a hydraulic pump in the wheel well there are several in there and at times make a lot of noise. Once that PDU cranks the leading edges in they quit running, there is no continuous movement after that. Sound can easily translate through structure so that the offending component isn't always located at the spot you hear the noise.

I was sitting in a 57 at ATL on my way to SEA one day and heard that familiar sound, of a pump going bad. After you listen to them day after day doing funtional tests on new ones you get to know what they're supposed to sound like, healty or not. In this case not. I told the flight attendant to let the pilot know that a mechanic back here swears he has a bad pump.

I think they knew something was amis already because minutes later maintenance came through and fooled with things and eventually determined we had a bad pump that had been written up previously but they were just milking it. We had to de-plane and get another jet to fly. That's the only time I've ever had to change planes due to maintenance in all the years I've flown.

 

You suspect wrong. The 757 does not have dumping capability! unless its a leak! Landing with flaps 15 is Vref30+20 which is not a big deal when compared to a no slat/flapper.

 

there is not a big spread between max gross and landing like the big jumbos. In this case, 255, 500 max gross weight and a max landing of 210,000 lbs. You can land overweight but have to write it up in the log book and do required inspections. If your on fire or need to return ASAP, you dont care if your overweight!

FAR 25.1001 was enacted stating a jettison system was not required if the climb requirements of FAR 25.119 (Landing Climb) and FAR 25.121 (Approach Climb) could be met, assuming a 15-minute flight. In other words, for a go-around with full landing flaps and all engines operating, and at approach flap setting and one engine inoperative, respectively.

Since most twinjet airliners can meet these requirements, most aircraft of this type such as the Boeing 737 (all models), the DC-9/MD80 and Boeing 717, 757 the A320 family and various regional jet ("RJ") aircraft do not have fuel dump systems installed




Cheers