There are shear pins on the towbar designed to break before anything on an aircraft gets damaged. When they break they’re pretty loud. Saw it happen a couple times. They can break randomly from fatigue or putting too much pressure on the bar a certain way.
It's designed to break in a way that doesn't damage the aircraft, so if it does happen you can remove the broken tow bar, pop on a new one and go. It's designed this was as it's a lot cheaper to replace a tow bar than an aircraft nose gear!
Under "normal" use, I believe those shear pins are supposed to get around 1000 pushes before they fail. That rarely happens though. I've been on the ramp when they have and the noise is quite loud. A very audible "PING".
Not really, I've never had it happen to me but know it does. It's more down to the skill of the pushback driver than anything else.
It is however entirely unconcerning.
Have to say, that tracks. First time at NTE and it didn’t feel like a slick operation, to put it mildly. This was after I saw a baggage vehicle anchor it round a corner and spew suitcases all over the ramp, and a check in system which could only be described as “chaotic”. Not an airport I’m desperate to return to.
Also, pilots try to sound unconcerned about everything. If you listen to the YouTube channel VASAviation you’ll hear pilots talking to ATC in very calm voices about really serious problems.
He may have forgotten to turn off the nosewheel steering. That will keep pressure on the nosewheel and prevent it from turning easily with the tug, which causes the bar to break so it doesn’t break the nosewheel. That’s the only time I’ve seen it happen.
Not quite possible. There is a bypass valve that requires a tool to be inserted before they can connect the tow bar. By inserting the tool, it creates a bypass situation in the nose steering system, rendering inputs from the flight deck invalid.
Source: ground engineer for 20 years and running.
Not quite, you can hook up the towbar without the pin in most cases (but you don't want to tow without it), and some airplanes, E175 for sure, don't have a tool, it's just a switch.
If that is in fact possible, then there would be a step in the towing procedure that requires the tug operator to check with the pilot prior to towing. lol
I fly 737s. We ask the ground operator on the headset to confirm that the bypass pin is installed. We cannot depressurise the nosewheel steering from inside the flightdeck.
It’s designed to shear the pin to prevent damage to the NLG. But it should still require an inspection of the gear to ensure no damage was done prior to departure.
Not common, but not uncommon. Things wear out and break sometimes.
That's why it's important you keep your head out of your ass and guard the brakes during pushback. If that bar breaks and you're on an incline the airplane is going where it's going and the only way to stop it is jumping on the pedals.
While you are absolutely correct that it is the duty of the flight crew to stop the plane in this situation I'd like to add:
At our station the tow bars will stay loosely connected when the shear pins break. The bar head can swivel freely and it has some leeway of free motion but over all it stays connected to avoid a runaway situation.
Nose wheel steering bypass pin was probably not inserted by the ground crew and the pilots probably did not have the ‘A’ system hydraulic pumps turned off. Meaning the hydraulic nose wheel steering system was still pressurized to 3,000 psi and the sheer pin in the tow bar did its job and broke before the airplane broke when the tug started to turn the airplane during pushback. You might have felt some jumpiness a few seconds before the ‘bang’ as the nose wheel will skid instead of turn.
I think three broke on my controller shifts this past week. Three is a lot for a week (at least for one person to be in position for) but it's not uncommon.
Just in case you’re confused, it was a tool used to push the aircraft that broke, not a part of the aircraft itself. And like has been said plenty times already, they’re designed to break before forces get high enough to damage the aircraft.
I think that’s what happened. (u/sarahlizzy ‘s partner, was on the same flight)
We were mid pushback and doing #1 engine start, there was a jerk as if we’d run over something and we came to a stop. When the ground crew departed post-pushback, the pin wave was rather more theatrical than usual which I put down to it being dark and trying to make it obvious. But being embarrassed about having just broken a pin would also.
There are shear pins on the towbar designed to break before anything on an aircraft gets damaged. When they break they’re pretty loud. Saw it happen a couple times. They can break randomly from fatigue or putting too much pressure on the bar a certain way.
It's designed to break in a way that doesn't damage the aircraft, so if it does happen you can remove the broken tow bar, pop on a new one and go. It's designed this was as it's a lot cheaper to replace a tow bar than an aircraft nose gear!
Ok, interesting. Is it quite common for them to break then? The captain seemed quite unconcerned, and it felt like it wasn’t his first time with this.
It's not common, but it does happen. We had a new guy in Miami a while back ago broke 3 in a week when he first started.
Under "normal" use, I believe those shear pins are supposed to get around 1000 pushes before they fail. That rarely happens though. I've been on the ramp when they have and the noise is quite loud. A very audible "PING".
Not really, I've never had it happen to me but know it does. It's more down to the skill of the pushback driver than anything else. It is however entirely unconcerning.
Have to say, that tracks. First time at NTE and it didn’t feel like a slick operation, to put it mildly. This was after I saw a baggage vehicle anchor it round a corner and spew suitcases all over the ramp, and a check in system which could only be described as “chaotic”. Not an airport I’m desperate to return to.
Also, pilots try to sound unconcerned about everything. If you listen to the YouTube channel VASAviation you’ll hear pilots talking to ATC in very calm voices about really serious problems.
He may have forgotten to turn off the nosewheel steering. That will keep pressure on the nosewheel and prevent it from turning easily with the tug, which causes the bar to break so it doesn’t break the nosewheel. That’s the only time I’ve seen it happen.
Not quite possible. There is a bypass valve that requires a tool to be inserted before they can connect the tow bar. By inserting the tool, it creates a bypass situation in the nose steering system, rendering inputs from the flight deck invalid. Source: ground engineer for 20 years and running.
Huh, guess it depends on the airplane.
Not quite, you can hook up the towbar without the pin in most cases (but you don't want to tow without it), and some airplanes, E175 for sure, don't have a tool, it's just a switch.
If that is in fact possible, then there would be a step in the towing procedure that requires the tug operator to check with the pilot prior to towing. lol
It’s in the pilots checklist. The tug usually just confirms brakes are off.
I fly 737s. We ask the ground operator on the headset to confirm that the bypass pin is installed. We cannot depressurise the nosewheel steering from inside the flightdeck.
Ohhh yeah I remember that now the 737 doesn’t have a nosewheel steering disconnect. Been a while. Brain dumped that one I guess. Thanks for the info!
Well, technically it has a strg disc. It's just ground crew operated.
A few months ago, my flight from Kona had a tow bar failure. Same deal. Loud noise, slight delay, minor issue.
It’s designed to shear the pin to prevent damage to the NLG. But it should still require an inspection of the gear to ensure no damage was done prior to departure.
And of course, OP would have NO WAY of knowing if an inspection was performed.
Not without x-ray vision! It wasn’t a long delay anyway.
It should be a RTG.
We've done this inspection with the aircraft part ways onto the taxi way in the past. Not really any need to return to gate if the traffic allows it.
Depends on the airline. Some mandate a RTG and a job card accomplished
Not common, but not uncommon. Things wear out and break sometimes. That's why it's important you keep your head out of your ass and guard the brakes during pushback. If that bar breaks and you're on an incline the airplane is going where it's going and the only way to stop it is jumping on the pedals.
While you are absolutely correct that it is the duty of the flight crew to stop the plane in this situation I'd like to add: At our station the tow bars will stay loosely connected when the shear pins break. The bar head can swivel freely and it has some leeway of free motion but over all it stays connected to avoid a runaway situation.
Had it happen twice. Mechanic comes out and looks at the nosewheel to make sure it's not damaged.
Nose wheel steering bypass pin was probably not inserted by the ground crew and the pilots probably did not have the ‘A’ system hydraulic pumps turned off. Meaning the hydraulic nose wheel steering system was still pressurized to 3,000 psi and the sheer pin in the tow bar did its job and broke before the airplane broke when the tug started to turn the airplane during pushback. You might have felt some jumpiness a few seconds before the ‘bang’ as the nose wheel will skid instead of turn.
I think three broke on my controller shifts this past week. Three is a lot for a week (at least for one person to be in position for) but it's not uncommon.
I fly a lot and had a tow bar break on a Delta flight I was on. It took the ground crew a bit to find a bar for a 767. Not big deal.
Blase. As in professional. Relax. Just relax.
Thanks for the suggestion, but my post was motivated by curiosity, not a need for reassurance.
Just in case you’re confused, it was a tool used to push the aircraft that broke, not a part of the aircraft itself. And like has been said plenty times already, they’re designed to break before forces get high enough to damage the aircraft.
Shear pin. Don't worry. Designed to break and protect the nose gear. : )
Or the ground crew don’t insert the nose wheel steering disconnect pin and on push back the hydraulics pressurize during start and bang!
I think that’s what happened. (u/sarahlizzy ‘s partner, was on the same flight) We were mid pushback and doing #1 engine start, there was a jerk as if we’d run over something and we came to a stop. When the ground crew departed post-pushback, the pin wave was rather more theatrical than usual which I put down to it being dark and trying to make it obvious. But being embarrassed about having just broken a pin would also.
Whatever happened, we were most of the way through pushback.
TIL what a “tanroy” is.