View Full Version : Boeing Undercarriage Retraction

14th Jul 2015, 16:27
Mrs Flo was recently on a long haul flight on a 744 and commented that the noise and vibration from the undercarriage (she was back at doors 4) during retraction, was much greater than normal ( she has been 777and 747 CC for going on 25 years so has heard it sufficiently regularly to comment I believe). She had commented on it during the first sector but noticed it again on the second, while of course it may well be nothing she asked me about it and I'm not sure it's the same as the bus.
Question is, does auto brake activate after lift off and stop the main gear from spinning and is it linked to the auto brake used during a rejected take off. Would tyre wear and wheel balance cause vibration and is there any indications of tyre pressure and or vibration on the flight deck? Finally do the flight crew have to do anything to initiate wheel braking during retraction?
Many thanks

Amadis of Gaul
14th Jul 2015, 16:49
The answer to your question is yes.

14th Jul 2015, 19:03
And no the breaking after takeoff is automatic.

14th Jul 2015, 19:21
...the breaking after takeoff is automatic....

After which the picking up of the pieces is a manual affair ...

Pre-retraction wheel braking is an automatic function.
Now IF an aircraft is dispatched with a wheelbrake deactivated, that one wheel could be spinning for a while, possibly with associated noise. It is also possible that the procedure then describes to wait a certain amount of time with retraction to let the spinning reduce to an acceptable level before retraction. The period of flight with gear down would also be noisier than usual after take-off.

14th Jul 2015, 19:46
I'm sorry I meant braking

14th Jul 2015, 19:47
Per the MEL if the brakes are deactivated by just capping the line and not using the brake deactivation tool you leave the gear down two minutes to allow the wheels to spin down.

14th Jul 2015, 20:15
Thanks for the expansion to the first answer......Pretty much as I expected. Think it might be pertinent to advice the CSD/CSL if was an MEL item as they may well, as in this case, wonder what the difference or problem is. Of course it also may not be this, I've read of RTOs due to nose and main gear shimmy all caused by wear on the shoulder of the tyres and even tyre pressures....

15th Jul 2015, 05:32
During retraction, some of the hydraulic pressure used for retraction is ported to valves which activate the brake system to de-spin/brake the wheels. The 747-400 "autobrake" system per se, is not used to carry out de-spin.

It's all done with mechanical valves. I suppose there could be faulty components, leaks, etc. It wouldn't hurt to tell someone about the unusual noise, especially if the person is a frequent flyer like Mrs-Flo.

Did the noise continue well after retraction?

15th Jul 2015, 16:44
On 2 occasions, same route legs 1 and 2 but different aircraft. The second sector yes, the wheels seemed to continued to run for a while after gear retraction, from her point of view, and after the main gear doors had closed. She had mentioned it on the first leg with little or no response and certainly no follow up. Second time reported it to the CSD but it went no further and the flight deck said it seemed normal to them so not to worry about it. It was as much my trying to explain the system and how it worked on the bus I now fly and the previous type (albeit a first generation classic that had a big wood and rubber block rubbing strip for the nose gear) and wondering how the 74/77 systems by Boeing worked in comparison. Thanks

16th Jul 2015, 08:25
The 747-400 nosewheel de-spin is the old style, too.... A fire-resistant pad attached to spring metal which contacts the tyres. In the forward zone, it sometimes sounds like a circular saw cutting through timber (quite a surprise to first-timers).

18th Jul 2015, 07:22
If the vibration was THAT noticeable back at door 4 on the '74, the problem of auto de-spin not working was most probably affecting the body gear, not the wing gear, which of course, you can't see!
Body gear wheel balance/de-spin problems are significantly more evident in the way of vibrations felt in the pax cabin.

anson harris
18th Jul 2015, 08:25
A fire-resistant pad attached to spring metal

I might be wrong but I think it's called a Snubber.

19th Jul 2015, 21:59
Following on from these answers, and thank you for them all I have passed them on, was/is there any manufacturers that have a spin up system other than, of course, the moment of rubber and runway interface?

20th Jul 2015, 09:23
was/is there any manufacturers that have a spin up system other than, of course, the moment of rubber and runway interface?

I think it has been mentioned on the forum previously. I vaguely recall a system fitted to B52's. Not sure if it's still in use.

20th Jul 2015, 10:33
was/is there any manufacturers that have a spin up system other than, of course, the moment of rubber and runway interface?

I was unaware of the B-52 setup - interesting NSEU!

Other than that, Mr. Flo, no large aircraft I know of have such a thing, although it was something fitted to Learjets for use on unimproved runways (gravel).

NASA or the USAF, I can't remember which, studied tire wear on large aircraft and discovered most tread wear is due to cornering forces and not smoky touchdowns.

20th Jul 2015, 10:34
I flew as a passenger on a straight wing Citation II a few years back in order to be positioned to pick up an aircraft. This aircraft would occasionally land on gravel runways. The crew told us that the nosewheel had an auto-spinup feature in order to reduce the likelihood of gravel being picked up and hitting the belly. This is part of the optional gravel kit installation.

A look at the nosewheel showed that there did appear to be some sort of add-on to the axel(perhaps axle) portion of the wheel.

There is mention about it in this link.

1977 | 1244 | Flight Archive (http://www.flightglobal.com/pdfarchive/view/1977/1977%20-%201244.html)

23rd Jul 2015, 05:45
I am pretty sure the process is very common amongst jet aircraft. I can speak for the DC10/MD11 aircraft as I have performed this check during heavy MX visits. Hydraulic sequence logic ports roughly 400 PSI to the brakes from the time the retract actuator is commanded until the gear is up.