*BANG!!!* What the hell was that?

boeingboy · Post by **boeingboy** » Wed Feb 28, 2007 10:58 pm

I would have to say that if the crew didn't get out and look and you didn't go back to the gate - the ground crew forgot to install the steering bypass pin and when they tried to turn the aircraft during pushback, they boke the shear pin on the towbar.

If thats the case - no big deal. Install another shear pin and the bypass pin and resume the push.

sinjin · Post by **sinjin** » Thu Mar 01, 2007 1:42 am

I have lost a tranny on a push back that made me think that the would was comming to an end. got a second tug to pull the first one out of the way and then used the second one to finish pushing back the plane

Mitch Cronin · Post by **Mitch Cronin** » Thu Mar 01, 2007 5:18 am

Shear pin on the towbar is most likely, just as Boeingboy says... or maybe even a broken towbar itself- from exactly the same cause... If the towbar breaks it'll make quite a bang and shudder... usually the shear pin going won't be quite so dramatic.... rarely any big deal in either case.

Mitch Cronin · Post by **Mitch Cronin** » Fri Mar 02, 2007 8:27 am

Yeah... when the bar is under the strain needed to break a shear pin the part that remains fixed to the nosewheel snaps back upon the instant the pin fails... that's the bang and the vibration.... the nosewheel is securely mounted to the airframe, so the whole airframe feels that shudder.

Troubleshot · Post by **Troubleshot** » Fri Mar 02, 2007 3:08 pm

The vibrations were probably just the engine lighting off, the CFM 56 does make some hum's when starting...and the time line of the bang would make sense because you are starting to build Hydraulic pressure right before light-off.

FastFlyBy · Post by **FastFlyBy** » Sat Mar 03, 2007 3:22 am

Mitch Cronin wrote:Shear pin on the towbar is most likely, just as Boeingboy says... or maybe even a broken towbar itself- from exactly the same cause... If the towbar breaks it'll make quite a bang and shudder... usually the shear pin going won't be quite so dramatic.... rarely any big deal in either case.

More likely the sheer pin. I can't imagine a '37 towbar breaking, has it happened before?

wrc · Post by **wrc** » Sat Mar 03, 2007 4:27 am

Could have been the sheer pin. In Ottawa the ramp has a slight slope down towards the new terminal with a resulting extra strain on the tug & bar starting the push.

- How did the crew, inside the cockpit, determine the airplane was airworthy? After a noise like that, I wouldn't have so much as turned on a strobe without taking a look for myself.

If the airline was WestJet in Ottawa the reason they didn't look themselves is that with only one aircraft at the terminal our AME on duty usually sits in the van at the gate facing the plane till we leave. So if it was WestJet the AME himself most likely gave the thumbs up to the pilots.

Mitch Cronin · Post by **Mitch Cronin** » Sat Mar 03, 2007 5:51 am

FastFlyBy wrote:More likely the sheer pin. I can't imagine a '37 towbar breaking, has it happened before?

Agreed, more likely the pin... but yes, I've seen towbars break... I think usually it's been determined afterward that the shear pin in use was not correct (or not a shear pin at all - a steel bolt will do that) ...not sure if I've ever seen that with a '37 though. ...I recall seeing it happen twice in a row with a '47... the whole head broke off the bar (in that case the nosewheel steering bypass had just been rigged -incorrectly.)

Troubleshot · Post by **Troubleshot** » Sat Mar 03, 2007 6:45 am

cpl_atc wrote:
Troubleshot wrote:The vibrations were probably just the engine lighting off, the CFM 56 does make some hum's when starting...and the time line of the bang would make sense because you are starting to build Hydraulic pressure right before light-off.
If a CFM56 sounded like that on startup, you'd have a very hard time selling any seats on a NG37. (I wasn't being dramatic when I said it sounded like a catering truck driving into the underside of the plane.)

Roger that.