Brake temp accuracy

[bigmountain]

guys this topic is generating a lot of contraversy and discussion on our fleet.

On the B777 the brake temp indicate accurately after approx 15 min.
There are two schools of thought .
1) Incase of a High speed abort. since the correct temp of the brake will only be known after 15min it means that the actual temp and the aircraft can continue to taxi to stand within the 15 min.
2) the other school of thought is: since the brake temp will only give an accurate reading after 15 min , one should consult the the QRH recommended brake cooling schedule. If the table indicates that the tyres are in the fusible plug melt zone then the aircraft should be cleared form the runway and chocked immediately

comments and if possible any supporting evidence or documention or links will be highly appreciated.


thanks

Bigmountain

[Notso Fantastic]

1 is a no-no. You may have hot brakes. Taxi hot brakes to the stand may make the situation worse and cause deflation on the stand (and fire risk at the building). I would say you should consult the QRH to assess the level of risk. If high, then taxi minimally clear and set park brake and get assistance immediately with external inspection. If very very high, don't even move off the runway!

[RaTa]

High speed abort on a heavy weight TO, taxi off the runway if it is safe and can be done quickly (ie no 180 turns), then consult the QRH brake cooling schedule!

[Engineer]

From an FCOM abnormal procedure (not 777)

Brake overheat light on(temp >400C)

Brakes.............................Minimum braking Avoid dragging brakes

Advise ramp personnel to stay clear of main landing gear

Caution

Do not attempt takeoff if overheat light on The max quick turnaround time is not required if 10 mins after parking without artifical cooling warmest brake temp indication is 400C or less. This will provide fuse plug integrity but does not account for brake capability during rejected takeoff


At BA/KLM this procedure was further developed using the quick turnaround charts in the AOM to relate brake temp to WAT conditions at the time of abort Resulting in defined actions depending on brake temp indication. These were an expansion of that quoted above. However you could at least taxi off the runway if tyres still in tact.

As a rule of thumb used 45C per 20 mins as a ground cooling time

[411A]

Accurate only after 15 minutes, on the 777?

Gosh, the good 'ole L1011 did better than this...a lot better.
And, quite accurate too.;)

[alexban]

411A , you got it wrong.
" The brake temperature indication do not provide instantaneous readings of brake conditions,as brake temperature tends to rise for 10 to 15 minutes after brake application.The values tend to increase for 10 to 15 min after the brakes are used."- FCOM
This is generally true,pure physics, and I doubt very much that the good"ole L1011 had some kind of out of earth brakes that disipated the energy imediately after braking. ;)
If you'll taxi to the stand after high speed reject you'll increase the amount of heat in the breaks and,most likely ,you'll melt the fuses.It happened more than once.
Brgds Alex

[Notso Fantastic]

We did a 120 kt reject in a heavy Classic. Taxied clear, got inspected by the LHR firecrews, then did a slow, gentle taxi to the old B25 or NE corner of Terminal 1- maybe 3/4 mile tops. Once on stand, the plugs went on one side wing gear, so gentle lean over. On reflection, we should have kept clear of attaching ourselves to buildings!

[411A]

No, alexban, I didn't 'get it wrong, you mis-understood what I wrote.
I fully realize that brake temps rise, and continue to rise for quite some time, after very heavy braking, as with a rejected takeoff at higher speeds.

For example, I have done two rejects in TriStar equipment, both oddly enough from about a hundred ten knots.

Brake temps indicated 400 at the end of the stop, the aircraft was taxied clear of the runway, and parked at a more remote parking bay, rather than a jetway.
Temps stabilized at 500 or so, within about 5 minutes.
Ground crew were advised to remain well clear, and no tires deflated, fortunately.

The brake temp indications on the big Lockheed three-holer were quite reliable...at least in my experience anyway.

Your milage may vary.

[alexban]

411 the same is valid for 737 ,777 brake indicator.They are accurate,but the problem is the temp will continue to increase,so if you see 400-500 after braking you can be sure the temp will increase in the next 10 min,so no taxi, as NF did,which further increased the sidewall temp ,thus melting plugs.

[Notso Fantastic]

wrt the energy of the abandon take-off, I wrote:
If high, then taxi minimally clear and set park brake and get assistance immediately with external inspection. If very very high, don't even move off the runway!

Taxiing a 747 creates a lot of wheel heat. After ours, which was on the high side, but not a max V1 abandon, we braked rather heavily. That extra taxi caused a lot of trouble. I really think you should keep it minimal- we would probably have got away without losing any wheels if we had just moved clear of the runway and stopped. As for a max energy stop....don't even move- close the runway!

[df1]

How do these fusible plugs work exactly?

[Notso Fantastic]

When the hub gets really hot, and they can get to the point of glowing red on a full speed reject, the plugs will melt and the tyre will deflate safely. They can blow out like a bullet which is why evacuees should not stand beside them- either in front or behind the wheels, and preferably upwind of the aeroplane!