United 777 drops wheel during takeoff KSFO

[Yancey Slide]

https://twitter.com/BNONews/status/1765855107185275265

Did some damage to parked cars.

https://twitter.com/CANews_Watch/status/1765843896008110403

[BFSGrad]

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.

[Yancey Slide]

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.

Yeah, the purported takeoff video seems to be the left MLG aft right tire?

[Boeing Junkie]

Yeah, the purported takeoff video seems to be the left MLG aft right tire?
Cali Planes caught it on their live YouTube stream. Need to start watching from about 11:23 am

[BFSGrad]

Now to win the title of 777 Trivia King, how much does a 777 main gear wheel/tire weigh and would the tire have still been rotating at the time of separation?

[JanetFlight]

https://www.youtube.com/watch?v=Iz-yv7QtNLU

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

[BFSGrad]

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??? TksWhen 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.

[aeromech3]

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.

[Chris2303]

I wonder how high it bounced?

[KRviator]

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.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...

[DaveReidUK]

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.

[Ikijibiki]

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.

[San Diego kid]

Look at the pictures, definitly not only a tire.

[DuncanDoenitz]

BBC footage shows an apparently intact wheel/tire assembly in the carpark.

[Boeing Junkie]

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1792x828/img_9039_a8deac80af0d56752e36541b34eead72d35014a5.png
That appears to be a fully intact wheel and tyre according to the ABC News footage.

[FUMR]

The good thing is that it didn't hit any person!

[MechEngr]

A photo of the errant tire, with police car for scale.
https://cimg6.ibsrv.net/gimg/pprune.org-vbulletin/696x233/tire_5db47fe91860690cebb0b5ca7bae4fe8917867a9.png
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:
https://youtu.be/gjnwAxDh7rQ?t=34

[aeromech3]

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.

[MechEngr]

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.

[visibility3miles]

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/news/tire-falls-off-united-airlines-plane-after-san-francisco-takeoff-damages-cars-in-parking-lot/ar-BB1jwGZF


https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/1360x2000/united_wheel_2_ht_gmh_240307_1709850577845_hpembed_11x16_5b7 cbb2350f5806b1fce3386d832e4ac94373b71.jpg

[CV880]

Re post #10 AFIAK tire pressure indication on EICAS is standard on all 777's but I was told many years ago United deactivated/removed it after delivery.

[DaveReidUK]

If I'm not mistaken, the video appear to show the wheel migrating slowly off the hub before in finally departs, rather than letting go instantaneously.

[Sailvi767]

The good thing is that it didn't hit any person!

It was a violent impact according to the owner of the car it hit. He stated the impact was so hard it made his 2023 Ferrari look just like a 2005 Toyota Corolla. He is expecting United to replace the Ferrari!

[jethro15]

It was a violent impact according to the owner of the car it hit. He stated the impact was so hard it made his 2023 Ferrari look just like a 2005 Toyota Corolla. He is expecting United to replace the Ferrari!
So would I! (Must consider replacing my Astra - Aviva, it's said in jest!)

[Matt48]

Plane carrying 235 forced into emergency landing after wheel falls off during takeoffA United Airlines jetliner bound for Japan made a safe landing in Los Angeles after losing a tire while taking off from San Francisco.
See less

[Matt48]

All good, made a safe return and landed uneventfully, after all there were still 11 wheels left on the mains.

[DIBO]

https://www.pprune.org/accidents-close-calls/658031-united-777-drops-wheel-during-takeoff-ksfo.html

[Bosi72]

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.

.

I am yet to find an aviation mechanics which will make Cessna wheels rolling silently without grinding metal sound whilst pushing the aircraft.

[Matt48]

The tire landed in an employee parking lot at San Francisco International Airport, where it smashed into a car, shattering its back window.
https://assets.msn.com/staticsb/statics/latest/views/icons/ArticleImageFullscreen.svg
https://img-s-msn-com.akamaized.net/tenant/amp/entityid/BB1jxdep.img?w=768&h=403&m=6&x=1539&y=564&s=60&d=60

[Bksmithca]

Being discussed here https://www.pprune.org/accidents-close-calls/658031-united-777-drops-wheel-during-takeoff-ksfo.html

[uffington sb]

A little more damage than just a shattered back window!

[aeromech3]

Just for info: Jacking a wide body airliner for wheel change, if the tyre is flat a crocodile style jack is needed to get under the bogie (truck). The video shows the centre wheel change which is why 2x jacks are required (jacking point near each end of truck) on other non six wheelers only one jack normally required; on wide-body mains almost impossible to jack using a handle, even 2 mtr long and two mechanics, instead these jacks have an air driven motor and yes MechEng correct info, best plan is the adapter hose from the old tyre to the jack, otherwise LP air bottles; these tyres would be in the 200psi+ range and filled with nitrogen
Of the B737, B727, B767, and B777 the B727-200 main wheel tyre is the biggest I have come across and was inflated to about 190psi. Normally after workshop assembly the tyre is fully inflated, placed in a steel cage for a 24hr leak test, the rubber expands a little and cooling causes some pressure loss, then for storage it is deflated to about 50%.
Bosi72, steel, multiplate brakes, have a lot of clearances for expansion etc, and can be segmented like a jig saw puzzle, as the rotors flop around with wheel rotation, they do contact the stators, hence noise, I know next to nothing about Cessna wheels; carbon brakes are a lot quieter.
On my last B747-400 spec circa 2004, the tire pressure monitor was an option, it has plus and minus points in my mind, as no flight engineer to kick the tyre on walk about :hmm: and the large difference in pressure between cold and hot destinations can cause quite a lot of confusion for the crew (same with my Mini Cooper S giving me distracting warnings and requiring the car to be driven to get a reading ugh!). Example I inflate wide-body main tyre to 190psi in Arabian Gulf, aircraft arrives in Manchester UK, overnight check finds tyre at 170psi, inflated, plane arrives back in Arabia tyre pressure 205psi and so it goes on and on.
Just found this: https://www.youtube.com/watch?v=uK89pcck0sk

[Matt48]

3000 airline mechanics at nearby United maint base at SF got to see the results of their handiwork firsthand.

[jolihokistix]

Is that the Ferrari in the foreground?

[TURIN]

Aeromech3, that's why tyre pressures are stated with regard to temperature. The AMM has a graph to show the nominal pressure at different temperatures.

[ozbiggles]

It was a violent impact according to the owner of the car it hit. He stated the impact was so hard it made his 2023 Ferrari look just like a 2005 Toyota Corolla. He is expecting United to replace the Ferrari!

Good luck with that, how long did it take for United to replace a guitar…2nd time I get to use that line

[BFSGrad]

A more comprehensive version of the comms associated with this incident.

There’s a tire going down the runway...

[Capt Quentin McHale]

Just taking a guess here, but, if the wheel or brake (or both) were changed and upon reinstallation of the wheel, the wheel nut lock bolts were NOT installed. What's to stop the wheel nut backing off and said wheel deciding to deplane?

Rgds McHale.

[aeromech3]

C Q McHale, see my post #18, direction of this inner wheel rotation, except during push-back, would tend to tighten the axle nut.

[Capt Quentin McHale]

aeromech3,

With respect, wheel rotation has nothing to do with tightening or loosening of said axle nut. The nut is torqued up against a keyed washer/spacer which in turn rests up against the outer wheel bearing face. This in turn holds the bevelled shape of the outer bearing against the matching bevelled shape of the outer bearing seat on the outer wheel hub (same for inner bearing and bearing seat assembly on the inner wheel hub), and it is this matching bevelled shape of the bearings and bearing seats that pretty much holds the wheel on the axle.
The wheel nut and washer/spacer are there to keep the whole assembly together and prevent lateral movement of the wheel and bearings on the axle. So, if the wheel nut was installed WITHOUT the wheel nut lock bolts , there is nothing to prevent the wheel nut eventually backing off and the wheel departing.

Rgds McHale.

[Junkflyer]

Have not worked on the 777, but on other wide bodies we would torque the nut to a specific value while spinning the wheel to seat the bearings.
It would then be backed off and torqued within the proper range and the the lock bolts were installed.
A sign off in the US should include installed per Maintenance Manual Reference number for the particular procedure.

[EXDAC]

and it is this matching bevelled shape of the bearings and bearing seats that pretty much holds the wheel on the axle.

Taper roller bearing naturally want to increase the separation between the inner races. Something has to oppose that natural separation force or the wheel will depart. An axle nut typically provides that retaining force. The axle nut holds the taper roller bearing with the correct loading and also keeps the entire wheel assembly on the axle.

The taper (or bevel as you describe it) of the bearings does not contribute to retaining the wheel. It does exactly the opposite.

In what way does the 777 wheel assembly defy these general principles?

[TURIN]

aeromech3,

With respect, wheel rotation has nothing to do with tightening or loosening of said axle nut. The nut is torqued up against a keyed washer/spacer which in turn rests up against the outer wheel bearing face. This in turn holds the bevelled shape of the outer bearing against the matching bevelled shape of the outer bearing seat on the outer wheel hub (same for inner bearing and bearing seat assembly on the inner wheel hub), and it is this matching bevelled shape of the bearings and bearing seats that pretty much holds the wheel on the axle.
The wheel nut and washer/spacer are there to keep the whole assembly together and prevent lateral movement of the wheel and bearings on the axle. So, if the wheel nut was installed WITHOUT the wheel nut lock bolts , there is nothing to prevent the wheel nut eventually backing off and the wheel departing.

Rgds McHale.
You are assuming the spacer and lock nuts were fitted.....

[Capt Quentin McHale]

EXDAC,

You are indeed correct.

Turin,

Not assuming anything, just saying without lock nuts the wheel nut may back off.

Rgds McHale.

[TURIN]

Turin,

Not assuming anything, just saying without lock nuts the wheel nut may back off.

Rgds McHale.
That isn't in doubt.
No idea how we got here, I think two or three of us are talking at crossed purposes.

[Capt Quentin McHale]

TURIN,

Agree, however I should have worded it better.

Rgds McHale.

[aeromech3]

Just seen Stig shift, I ignore his comments, as far as I am concerned, if UA shop did the NDT or the bearing was over-loaded by torque or lack of grease or the wheel had been subject to very high temperature on earlier flights due to hot brakes.
No doubt there will be a few more to add to those possibilities. That is the brake heat sheild in the background.
https://cimg9.ibsrv.net/gimg/pprune.org-vbulletin/187x340/wheel_nut_ok_e137d8c7ca866c8d47cfab96c3c4e4433fd2468c.png

[Rebus]

It is possible to seat the washer against the shoulder of the axle and not on the axle itself but it should be noticeable. The safety bolt holes just about line up. I've also seen the tapered washer fitted back to front, again noticeable.

[ST Dog]

https://youtu.be/q4Dd50d45Bc?si=TrZHbKD-f3UY8nOj&t=476

At 7:56-8:10 the brakes appear intact. Looks like the axel nut came off.

[JRBarrett]

https://youtu.be/q4Dd50d45Bc?si=TrZHbKD-f3UY8nOj&t=476

At 7:56-8:10 the brakes appear intact. Looks like the axel nut came off.

No it did not. Pictures have been published of the axel of the incident aircraft after it landed at KLAX. See post number 47 just above.The axel nut and its locking bolts are still intact and installed. It appears either the wheel hub failed and/or the bearings disintegrated.

[ST Dog]

No it did not. Pictures have been published of the axel of the incident aircraft after it landed at KLAX. See post number 47 just above.The axel nut and its locking bolts are still intact and installed. It appears either the wheel hub failed and/or the bearings disintegrated.

Just saw the picture at 2:30 in Juan's video today.
https://youtu.be/rN256wwVwrs?si=tqkZyYJeo-Ml0ilG&t=150


Nothing in post #47 made me think it was a photo of the incident aircraft.
Had to look up Stig shift. Then it's buried 20 minutes into a 45minute video not focused on the incident.

[MechEngr]

Sometimes the dildo of fate arrives unlubed. Possibly that was also the case for the bearings on that wheel assembly. Time to check the storeroom to see how long the bearings have been on the shelf or if the new guy knows they need to fill with grease before installation.

Also check to see if the brakes were dragging. Had that happen on a car because the internal rubber sleeve in the brakeline collapsed; fluid could pump out but would not be allowed back. Wheel got to over 200F at the center.

If it's the brakes aren't there temp probes to detect overtemp?

[aeromech3]

In our small aircraft wheel shop, attached to my last hangar set up, the specific greasing of the bearings was strictly applied and itemised on the wheel build sheets (preferred manufacturer had a red colour); the bearings stayed with the wheel and a dummy retainer long bolt with plastic dustbin shape wheel protectors keep the assy together.
The grease retainer (bonded rubber to metal disc/plate) would also be a contributing factor in the bearings life.
Did I understand, this aircraft had been overnight before the incident and yes brake temps are displayed, but who is looking; on older models they would have a green band etc and most Crew know that after T/O especially after short turnarounds or long taxi, they might leave the undercarriage down for longer to cool the brakes/wheels.
I have had aircraft arrive on stand, (mostly L1011) having had some newly fitted brakes at a previous night stop station and those steel brakes have been glowing hot; despite having a FE with the temperature read out on his panel, not a word over the headset; luckily for them we just divert the ground air con hoses onto those brakes before the fuse plug went.
Conversely I have had plugs blow on wheels, were the crew had not released the park brake after the chocks in signal!
The culmination of repetitive hot wheels would be a gradual loss of bearing grease or properties.
The incident aircraft outer bearing cage and rollers had likely disintegrated than the multi spokes of the wheel outer hub.
p.s. my memories of the Line/Ramp ended 16 years ago and so experiences today might be a lot different.

[exeng]

I am told by a person who works for United that this incident was a result of axle failure.


Kind regards
Exeng

[aeromech3]

I am told by a person who works for United that this incident was a result of axle failure.
The video's all show the axle intact and the inner bearing race and its outer track resting on the axle, only the wheel and outer race parts are missing.
No doubt as good practice the axle was changed having been subject to high stress and temperatures and subject within the incident.https://cimg2.ibsrv.net/gimg/pprune.org-vbulletin/555x360/wheelaxle_cfc72f99b5d620bb36ac7274f801ba49370c2b3e.png

[MechEngr]

That's what happens when they don't have the balls to work in aviation.

Ok, ok, probably tapered roller bearings but that's not a great basis for humor. Probably the spacer/a spacer was the first to go and after that it all degrades really fast.

[aeromech3]

Ref to the axle end in the picture, the number of threads visible would be quite normal, hence the axle nut is in the correct torqued position, hence most likely the spacer is still present, would you not agree MechEngr ?
To add, the position of the axle nut locking bolts look normal and as the holes in the axle are most precise and the slots in the nut give limited tolerance, the bolts look about mid slot.

My interest is to deflect any unwarranted criticism of the wheel change crew but also to acknowledge that this incident is more serious than a few bent cars. The incident happening off airfield is one of more consequence, but also if a similar incident befalls a wheel in a different position, the retraction of the U/C could be impaired or indeed jammed with more serious consequences.

[MechEngr]

The spacer in the bearing that keeps the rollers separated. If it is one piece it gets called a cage, but some bearings use individual spacers between the balls or rollers as it allows a better fluid film to form and presents a larger area to decrease the contact pressure.

The spacer on the axle, sure, it all looks in place.