shear pin failure egbb
 

I heard that yesterday an aircraft went TEC during pushback at EGBB, the captain requested he be pulled back to stand, the nose of the aircraft was then seen to be bouncing up and down. The “shear pin” I think it’s called sheared and the aircraft continued towards the tug, a shout to the flight deck eventually brought things to a stop. I am curious as to what experiences others have of this type of incident and how common this type of failure is.

I would hazard a guess of probably a couple of times a day at LHR..............:)

In my past life as a Ground Eng I experienced a couple of shear pins shearing usually due to an over zealous tuggy or a tight pushback angle, which can be quite hairy with engines running and a slippery ramp.

FYI just about all tow bars have a shear pin which is designed to shear before damage occurs to the the nose landing gear of the aircraft.

However I do recall an incident that occured to an MD80 where a solid ( non shear pin) towbar was used on an extremely icy ramp. The aircraft with park brake applied and both engines running began to slide forwards pushing the helpless towbar and attached tug backwards causing them to jack-knife , the tug eventually impacting the forward cargo door , tow bar still attached !!!:eek:

Tow-barless tractors, now that's a different story alltogether ............:ouch:

Not that uncommon an occurance. Can have several causes, a/c brakes not releasing, inexperienced tug drivers not being as smooth as they should be, fatigue building up in the pins over several months, or even the wrong pins (eg A320 rated pins in an A321 bar, but hopefully not the other way round). I've also had it happen on 737-200's, they don't have bypass pins so if there is an electrical interuption on push the steering pressurises and straightens the wheels, If the towbar is unhooked from the tug when it happens you hope your legs aren't in the way:eek:

Once during pushback of a heavy A321 the truck stopped abruptly, pin sheared of and aircraft continued its way back towards the terminal. Rampagent was yelling "Set parking-brake."

I didn't.......

Its only really an issue if your rolling backwards.
Pilots have to gently apply brakes to prevent the a/c rolling. Sharp braking will sit the a/c on its tail! If engines are started a little thrust can be used as brake.

Happens a lot.

Corroded and fatigued pins is a common cause. As is fitting the wrong size steering lockout pin.:\ :O

Groundhogbhx
The BA 737-200s had the lockout valve retrofitted after one too many incidents. "A pumps off " etc. Or was it B pumps, I forget, it was a long time ago.....:confused:

Just thought I'd mention that a couple of times after the push has completed on a brand new aircraft (this recently ocurred with a couple of Ryanair 738's) I think the cover that moves down to cover the hole where the bypass pin is inserted doesn't move to it's normal position because the paint is thick and new.

This will obviously wear away after time but I guess it may be worth checking that after the pin is removed, all is as it should be... I don't work on the ramp, these were details I sort of pieced together and (shock horror) assumed.

For some reason I have had a post deleted from this thread (I know that I posted it as I am now subscribed to the thread and I didn't do that manually).

Anyway my post went along these lines:

Not if you are the tug driver or the ground agent and the aeroplane is rolling towards you.

As said in initial post, the captain requested to pull back to stand. If all engines were running & being towed back to stand (i.e. tow forward), it would need the best tractor & the best tug driver for the job.

In this part of the world we try to avoid forward towing an airplane with all engines running (especially with the heavies).

Twas the B pumps. Only saw a retrofit once in a blue moon when I used to play with them but not supprised, I had a very close encounter when the bar stopped against my hand (which was against my leg) and my shift leader got taken off his feet (didn't actually break anything but had a lot of trouble in cold weather with that shin ever since!!):(

I thought this might be an issue!!.... Why then am I permitted to use the same towbar for A319, A320 and A321??

A319 positioning to BHX ) domestic ) rather than A321 full load to FUE, for example, same sheer pin, same load value for sheer rating...

surely sheer pins are for 'extreme' load protection...... Don't get me wrong.. I've had pins go for 'no' reason, simply coz they are old and corroded!!

737 towbar - used for enpty 737-500 and full 737-800.. slight difference in weight!!!

They should be changed regularly ( pins ).. but how regularly??? How often is a towbar used?? It doesn't have a counter on it!!

These days, a towbar 'should have an 'axial' and a torque' sheer pin, so as to cover all axis in loaded movement... But older towbars lack this!! One for both, or one for one and not the other....... You get me???

Not fool-proof, but there for a reason!! Headset cords are long and curly for a reason!!

If this was the incident that I heard about (horses mouth) then the scene was thus.... a/c cleared to push back subject to an a/c taxiing away from behind, Capt. relayed this and was asked to release brakes. Tuggy started the push, Capt realised that criteria for push not met, and relayed info to ground. Ground relayed info to tug, tug braked rather sharply, shear pin failed, a/c carried on, Capt stopped a/c (gently) with brakes, nose bobbed up and down a little. Lead to delays as the engineers had to have a good look at the nose wheel, which was undamaged. Conclusion, shear pin did the job it is designed to do as a/c was undamaged.

That wasn't the incident or if it was not how it occured as this incident involved being pulled back onto stand due to a tech problem.

Excuse me what is meant by TEC?

Short for Technical. The aircraft has gone tech, means that it has a technical problem.

One thing to remember, "when the shear pin shears it does not fail" it is designed to shear when a certain force is applied.

Failure of the shear pin would when it does not shear and the landing gear is damaged.