United 777 drops wheel during takeoff KSFO
Join Date: Jul 2005
Location: Honolulu
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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.
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.
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?
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.
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.
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.
No doubt there will be a few more to add to those possibilities. That is the brake heat sheild in the background.
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.
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.
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.
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.
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?
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?
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.
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.
No doubt as good practice the axle was changed having been subject to high stress and temperatures and subject within the incident.
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.
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.
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.
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.
Last edited by aeromech3; 14th Mar 2024 at 06:25.
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.
The spacer on the axle, sure, it all looks in place.
