United 777 drops wheel during takeoff KSFO
N226UA, 22-year-old 777-200. Video of landing at LAX shows both nose gear tires intact. Employee parking lot pics at SFO shows what is likely a main gear tire resting peacefully between the white lines. Apparently thumped a few cars before it came to rest.
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Yeah, the purported takeoff video seems to be the left MLG aft right tire?
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One question please...if nobody has seen or advised them, could the crew knew they lost one wheel? Any sort of advise in the cockpit??? Tks
When advised by Center that a tire may have fallen off of the aircraft, UAL 35 replied that they had no abnormal indications. Since UAL scooted right up to FL320, that would also seem to support that they thought all the necessary aircraft parts were heading to Osaka.
General wheel knowledge with Boeing commercials.
If it was just the tyre then a wheel flange failure would be suspect ( nearly unheard of since detachable flange wheels have been phased out for modern pax aircraft); if whole wheel and tyre then it looks very much it escaped just as the retraction braking cycle began (up line selection) and this happens to be the point at which the tenons would be aligned and the wheel could slip off ( same sequence for fitting a wheel unless you want to have a lot of fiddling to align each disc).
Don't know exact weight of the combo, but if a wheel change dolly is not available it is a job for two Mechanics (not the Hulk) to lift onto axle (may use a thread protector).
That particular wheel position, the rotation would have been in the direction of tightening the axle nut and so doubt it was just the locking bolt missing.
Info: I found a crack in a flange wheel (Visount circa 1966) using ultrasonice probe when older method was dye penetrant; commercial aircraft wheels are subject to NDT, as is the tie bolts, at regular tyre change intervals.
If it was just the tyre then a wheel flange failure would be suspect ( nearly unheard of since detachable flange wheels have been phased out for modern pax aircraft); if whole wheel and tyre then it looks very much it escaped just as the retraction braking cycle began (up line selection) and this happens to be the point at which the tenons would be aligned and the wheel could slip off ( same sequence for fitting a wheel unless you want to have a lot of fiddling to align each disc).
Don't know exact weight of the combo, but if a wheel change dolly is not available it is a job for two Mechanics (not the Hulk) to lift onto axle (may use a thread protector).
That particular wheel position, the rotation would have been in the direction of tightening the axle nut and so doubt it was just the locking bolt missing.
Info: I found a crack in a flange wheel (Visount circa 1966) using ultrasonice probe when older method was dye penetrant; commercial aircraft wheels are subject to NDT, as is the tie bolts, at regular tyre change intervals.
I wonder how high it bounced?
Last edited by Chris2303; 8th Mar 2024 at 18:44.
Doesn't the Triple have tyre pressure on the EICAS? Or is that a customer option and United didn't order it? Would have thought that'd be an easy way for the crew to confirm they still have 6 wheels on each MLG...
I notice that on the previous flight (CDG-SFO), after exiting the runway the 777 stopped for several minutes on Twy B before continuing to the gate.
It may well have been waiting for another aircraft to clear, of course, but might just be an indication of some issue that required maintenance attention after shutdown. The aircraft was on the ground at SFO for 24 hours before departing for KIX.
It may well have been waiting for another aircraft to clear, of course, but might just be an indication of some issue that required maintenance attention after shutdown. The aircraft was on the ground at SFO for 24 hours before departing for KIX.
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Has there been any clarity as to whether this was loss of a tire only or the whole wheel/tire together? Some of the reports I'm reading seem to use "wheel" and "tire" interchangeably.
BBC footage shows an apparently intact wheel/tire assembly in the carpark.
The good thing is that it didn't hit any person!
A photo of the errant tire, with police car for scale.
The brakes act directly on the rim so that the wheel cannot impart a load to the retaining nut. The retaining nut has two keeper bolts to keep it from turning and there is a hubcap that looks to me like it would prevent the two bolts from backing out of their holes. The hubcap protects the connection to the pressure monitoring system and has a band clamp to hold it in place.
I lean towards a fatigue crack in the axle where the retaining nut sits.The axle turns with the tire and is subject to cyclic loads. In contrast, car axles are fixed in rotation and the bearings and wheels rotate. The crack would be at the bottom of a thread or the inside corner where the threads stop - a place where plenty of brake dust would settle and cover the crack. I notice in the following video the axle is not scrubbed clean or specifically inspected.
It looks like the hubcap is missing, maybe from the impact load.
Interesting info about tire install:
The brakes act directly on the rim so that the wheel cannot impart a load to the retaining nut. The retaining nut has two keeper bolts to keep it from turning and there is a hubcap that looks to me like it would prevent the two bolts from backing out of their holes. The hubcap protects the connection to the pressure monitoring system and has a band clamp to hold it in place.
I lean towards a fatigue crack in the axle where the retaining nut sits.The axle turns with the tire and is subject to cyclic loads. In contrast, car axles are fixed in rotation and the bearings and wheels rotate. The crack would be at the bottom of a thread or the inside corner where the threads stop - a place where plenty of brake dust would settle and cover the crack. I notice in the following video the axle is not scrubbed clean or specifically inspected.
It looks like the hubcap is missing, maybe from the impact load.
Interesting info about tire install:
MechEngr!
The tenons of the rotors in the brake unit engage with the keys inside the wheel hub. The axle does not rotate with the wheel/tyre, heaven forbid. The axle nut with thick, sometimes keyed, washer acts on the outer wheel half bearing inner track and through the wheel to the inner half bearing against a deep spacer on the axle. The hub cap does rotate with the wheel, on most older Boeing's there are 4 bolts securing it to a flange on the outer wheel half rather than a clamp.
Hub cap missing? in the photo the wheel on the parking lot has the inner half facing up.
The video misses a few essential points:
1) the old tyre is mostly deflated before the axle nut is loosened.
2) For just a wheel change, unless a brake rotor alignment tool is available the old wheel, after jacking with brakes off, is manually rotated and then the brakes are applied; this ensures the rotors have not dropped and resting only on the bottom wheel keys;
as said previously, the alignment without this procedure is fiddly and entails long strong screwdrivers manipulating each rotor segment inside the wheel hub.
3) If the brake was replaced, after fitting+ connections (self seal hydraulics) the alignment tool is used and whilst a mechanic rotates the tool with the rotors inside the brakes are applied.
4) I see they have the axle thread protector in place, with the wheel dolly hydraulically pumped up, the wheel should slide onto the brake tenons and then the axle.
Not sure the hub cap would hold loose axle nut lock bolts, some installations the bolts are from in to out and quite short with slotted and S/pinned nuts. But this position wheel, LH inner, is unlikely to loosen an axle nut, any small drag through the outer bearing to the nut would tend to tighten it!
Possibilities aside from missing parts: Over torque, leading to bearing over heat and seizure and then axle failure; axle fatigue failure; wheel spoke failure though picture does not support this.
Note: this is only a brief description to support the video.
The tenons of the rotors in the brake unit engage with the keys inside the wheel hub. The axle does not rotate with the wheel/tyre, heaven forbid. The axle nut with thick, sometimes keyed, washer acts on the outer wheel half bearing inner track and through the wheel to the inner half bearing against a deep spacer on the axle. The hub cap does rotate with the wheel, on most older Boeing's there are 4 bolts securing it to a flange on the outer wheel half rather than a clamp.
Hub cap missing? in the photo the wheel on the parking lot has the inner half facing up.
The video misses a few essential points:
1) the old tyre is mostly deflated before the axle nut is loosened.
2) For just a wheel change, unless a brake rotor alignment tool is available the old wheel, after jacking with brakes off, is manually rotated and then the brakes are applied; this ensures the rotors have not dropped and resting only on the bottom wheel keys;
as said previously, the alignment without this procedure is fiddly and entails long strong screwdrivers manipulating each rotor segment inside the wheel hub.
3) If the brake was replaced, after fitting+ connections (self seal hydraulics) the alignment tool is used and whilst a mechanic rotates the tool with the rotors inside the brakes are applied.
4) I see they have the axle thread protector in place, with the wheel dolly hydraulically pumped up, the wheel should slide onto the brake tenons and then the axle.
Not sure the hub cap would hold loose axle nut lock bolts, some installations the bolts are from in to out and quite short with slotted and S/pinned nuts. But this position wheel, LH inner, is unlikely to loosen an axle nut, any small drag through the outer bearing to the nut would tend to tighten it!
Possibilities aside from missing parts: Over torque, leading to bearing over heat and seizure and then axle failure; axle fatigue failure; wheel spoke failure though picture does not support this.
Note: this is only a brief description to support the video.
Ah - there are the bearings - 3:55. Then I agree on the flambé seizure of the bearing melting the axle. I think it was a Dash 8?? that had that failure with a spinning wheel of fireworks before the wheel departed following takeoff. Yeah, if the axle isn't turning, but the hubcap is, then clearance won't matter - the bolts will machine exit grooves.
Someone pointed out that tire pressure is used to assist the operation of that jack.
This also fits with the theory that if one wants correct info - just make a post that is wrong and Boom! someone will come back with the right answer.
Someone pointed out that tire pressure is used to assist the operation of that jack.
This also fits with the theory that if one wants correct info - just make a post that is wrong and Boom! someone will come back with the right answer.
Wheel damages cars
United loses tire on takeoff from SFO, lands at LAX
Tire (wheel) lands on cars in employee parking lot. No injuries.
https://www.msn.com/en-us/travel/new...ot/ar-BB1jwGZF
Tire (wheel) lands on cars in employee parking lot. No injuries.
https://www.msn.com/en-us/travel/new...ot/ar-BB1jwGZF