Broken tow bar??
#1
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Broken tow bar??
I've had a recent string of significant delays taxiing to the gate after landing, usually related to the gate being unavailable, and on more than one occasion, needing both A) a tug to the gate and B) having the tugger (tower?) be delayed for whatever reason.
Today was the kicker. DL 718 landed 45 min early to everyone's jubilation; needed a tug to the gate, fine. Then I hear a loud bang, followed by the captain sheepishly on the com telling us that the "tow bar" snapped off, and they need to get a new one, inspect the damage, etc. Half an hour with the gate tantalizingly in sight before we could deplane!
Has anyone ever heard of a "tow bar" issue before? It reminds of that old Seinfeld joke where your auto mechanic can just make up what's wrong with your car and you don't know enough to argue with them -- "Oh, I need a new Johnson rod, of course!"
Today was the kicker. DL 718 landed 45 min early to everyone's jubilation; needed a tug to the gate, fine. Then I hear a loud bang, followed by the captain sheepishly on the com telling us that the "tow bar" snapped off, and they need to get a new one, inspect the damage, etc. Half an hour with the gate tantalizingly in sight before we could deplane!
Has anyone ever heard of a "tow bar" issue before? It reminds of that old Seinfeld joke where your auto mechanic can just make up what's wrong with your car and you don't know enough to argue with them -- "Oh, I need a new Johnson rod, of course!"
#2
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Likely it was a shear pin that broke. There are typically shear pins on either end of the tow bar, tug end and aircraft end. They are there as a sacrificial piece in case the loads are too much on either the tug or gear to prevent damage. Can happen for a number of reasons. SOP when one breaks, no matter which end, is to inspect the gear. I broke one once when repositioning a -700 to a hard stand and used too much brake on the tug and the empty weight of the aircraft put too much force on the shear pin and it broke.
#3
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What probably happened is the shear pin in the tow bar went (broke). The pins are designed to shear at a certain stress level which is at a point prior to when the stress would damage the aircraft nose gear.
ETA: Looks like Bay Bay Area Blue beat me to the point.
ETA: Looks like Bay Bay Area Blue beat me to the point.
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#9
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I don't know exactly what broke, but I was on a flight about fifteen years ago when the captain announced that the tow bar broke. We were being towed to a gate (I don't remember the airport or aircraft type) but there had been a loud noise as we stopped moving suddenly. We were delayed about fifteen minutes before we could start too move again.
Note to self: This is a reason to keep seat belt fastened on the ground when aircraft is moving.
Note to self: This is a reason to keep seat belt fastened on the ground when aircraft is moving.
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Take it from a retired ramp manager: They also break because the aircraft brakes are still engaged or someone forgot to lockout the nose wheel steering. Both of these scenarios are usually due to a lack of communication and result in a minor (internal) investigation to see where the failure was. As others have mentioned it also usually requires MX to have to inspect the nose wheel.
#11
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Take it from a retired ramp manager: They also break because the aircraft brakes are still engaged or someone forgot to lockout the nose wheel steering. Both of these scenarios are usually due to a lack of communication and result in a minor (internal) investigation to see where the failure was. As others have mentioned it also usually requires MX to have to inspect the nose wheel.
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As a few of us have noted, the tow-bars are designed to shear upon reaching a certain stress limit, which is supposed to be a lower stress limit than the stress that would cause damage to the nose-gear of the aircraft. However, each aircraft type has different weights and thus different stress levels which would result in damage, thus the tow-bar required would be based on the aircraft type.
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I'd say there's a very good chance that's what happened. It usually happens when the push (or pull) starts. It's possible the flightdeck didn't know why it broke, or maybe they did (i.e. if the brakes were still set), but either way I don't think they'd announce it over the PA.
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When we were at the legendary Delta DO in 2010, I overheard a conversation one of our group was having with a Delta tech ops employee, and they were talking about tow bars, and if you didn't use the right tow bar with a specific model of airplane, the tow bar could break, or, in the alternative the landing gear on the plane could be damaged. Something I had always taken for granted and never thought about.
So, as strange as it may seem, this is one of the many issues that the rampers and supervisors have to deal with in preparing a flight to leave.
So, as strange as it may seem, this is one of the many issues that the rampers and supervisors have to deal with in preparing a flight to leave.
#15
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The majority of towbar failures (shear-pins snapping) are typically caused by:
1. Abrupt starts/stops by the Push-back tug operator.
2. Flt crew not releasing brakes when they have advised ground staff that brakes are released and they begin to push while brakes are set.
3. Push-back tug operator not adhereing to the nose-gear steering limit marks painted on the nose-gear door; Push-back operator exceeds nose-gear steering limitation and the bar snaps.
ETA: 4. GSE MX installing incorrect shear bolts when repairing a towbar (as mentioned above, shear bolts have specific ratings), while rare, I have seen GSE maintenance staff accidentally use a lower-rated shear bolt by accident causing premature shearing (again, it's rare, but possible).
Inspection after a towbar incident is routinely required (based upon airline SOP) due to the fact that when a towbar shears, it can easilly make contact with the nose-gear tires and cause damage.
And yes, towbars often vary by aircraft, but many use the same IE: B777, B767, MD11, DC-10 all use the same towbar. The majority, however, are not interchangeable and are labeled for which a/c they will accommodate; they attach by different means, so you cannot connect an MD88 towbar to a B777, two totally different attachment mechanisms.
1. Abrupt starts/stops by the Push-back tug operator.
2. Flt crew not releasing brakes when they have advised ground staff that brakes are released and they begin to push while brakes are set.
3. Push-back tug operator not adhereing to the nose-gear steering limit marks painted on the nose-gear door; Push-back operator exceeds nose-gear steering limitation and the bar snaps.
ETA: 4. GSE MX installing incorrect shear bolts when repairing a towbar (as mentioned above, shear bolts have specific ratings), while rare, I have seen GSE maintenance staff accidentally use a lower-rated shear bolt by accident causing premature shearing (again, it's rare, but possible).
Inspection after a towbar incident is routinely required (based upon airline SOP) due to the fact that when a towbar shears, it can easilly make contact with the nose-gear tires and cause damage.
And yes, towbars often vary by aircraft, but many use the same IE: B777, B767, MD11, DC-10 all use the same towbar. The majority, however, are not interchangeable and are labeled for which a/c they will accommodate; they attach by different means, so you cannot connect an MD88 towbar to a B777, two totally different attachment mechanisms.
Last edited by Loadmaster; Apr 30, 2018 at 11:52 pm