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piratepete
31st Mar 2010, 16:57
Scenario:B767-300.Landing at 140,000kgs, slight tailwind, 13,000 foot runway, but at a very high elevation airport, circa 7700 feet.Everything is normal, on speed, on profile, touchdown tailwind is 6 knots from both tower and the IRSs.Touchdown occurs on the markers etc, ABs 3 selected, maximum reverse.

Result:Shortly after vacating the runway, ALL brake temps shoot up to 6s and 7s.....this seems to be an issue with the 767, not the 757 with a perhaps better autobrake software program.Any ideas on how to mitigate this problem?PP.

B-HKD
31st Mar 2010, 17:07
If the Autobrakes are indeed working correctly and commanding proper decel. rate and brake pressure, then I would say the only option you have is to try a lower decel. rate such as AB2 with full reverse. (of course only if performance allows for it)

puffo22
31st Mar 2010, 21:32
try this....
autobrake off
full rev until 100 kts then brakes on to stop and vacate at the end of the rwy
by

Gin Jockey
1st Apr 2010, 02:49
Autobrake software program? That's a bit fancy. There's no rocket science in this. All they do is decelerate the aircraft at a certain rate.

Regardless of the autobrake setting you are still putting a lot of energy into the brakes in the scenario you describe. Fairly heavy landing weight. High density altitude (i.e. high TAS). And tailwind. You would have been better off landing into wind (there's roughly 12 knots off your touchdown groundspeed right there) and using a lower autobrake setting (1 or 2) to let reverse thrust do more of the slowing down.

Pugilistic Animus
1st Apr 2010, 02:53
FAR 25 MBE limits for landing are pretty extreme,...you do have to stop though somehow:ooh:

PS you should use the braking procedures/methods/ auto brake settings as detailed by the company in the flight manual, or as prescribed in your line training :)

stilton
1st Apr 2010, 05:43
Out of curiosity, are you using steel or carbon brakes ?

169west
1st Apr 2010, 17:38
puffo22 suggestion seems pretty smart, but I will try AB 1 till 110 kts and then max manual with max rev well after the 80 kts call.
Or you can start with AB 3 and instead of keeping AB 3 till taxy speed, during the landing roll ask your PM to decrease the AB according to the rwy remaining and use all the 13k ft of LDA.

piratepete
1st Apr 2010, 19:52
I have a heavy weight landing tomorrow under similar conditions, so will try some new methods, and report back to you how it went, but this is certainly an ongoing problem.However this is what we get paid for as airline pilots, and I do enjoy it.My 47 times into and out of Kathmandu are not helping, but there you go.Thats only 4500 elevation, but the issue there is the very steep descent angle from 10 dme, its a normal descent angle from 5 dme, if you look at the charts.......cheers PP.

Pugilistic Animus
1st Apr 2010, 20:35
so will try some new methods,


New ideas are dangerous,...:=

parabellum
1st Apr 2010, 21:26
with max rev well after the 80 kts call.



A pointless exercise if you don't mind me saying so, all you will achieve is a lot more noise, increased risk of FOD and higher Tats. Reverse is most efficient immediately after touchdown and efficiency diminishes as ground speed diminishes.

I wouldn't reduce AB below 1 for the conditions you describe, probably not below 2 in practice. The AB is there for a purpose, it is more efficient than the human at rapidly applying pressure and modulating it as GS reduces(Those are Boeing's words, not mine, I just agree!).

piratepete
1st Apr 2010, 22:00
PUGILISTIC ANIMAL.

Dear Pug,
When you have something usefull to add, then please do so, in the mean time why dont you just keep your silly thoughts to your self......PP

Junkflyer
1st Apr 2010, 22:36
I wouldn't call following Boeing or company procedures silly.

DoNotFeed
2nd Apr 2010, 11:36
An easy way on the 67 with carbon brakes C or D is to calculate the total brake energy for brake on elevation, speed and weight.

There is a magic value of 40 millions ftlbs. Above you are in the caution zone below you are fine. Your source is the turnaround calculation and shows perfectly brake temperature for a given condition.

Compare the full brake distance with a certain AB distance and calculate from the normal landing table your distance required. This gives you the proper setting for distance available.

In other words look at the distance available select the proper autobrake setting from the table and as a example with 140 tons you are fine with AB 2.

Of course reverse thrust is of great value if it comes to brake temperature it is well shown in the brake energy table.

KTM is not a problem on this bird for the brakes, it is the missing runway end covered by a crookback shape. Most gys stop after 1/2 of the runway available......


best regards:ok:

sky9
2nd Apr 2010, 17:02
AB1 then use reverse thrust and additional manual breaking as (if) required towards the end. Aim to use the full 13,000 ft.

Pugilistic Animus
2nd Apr 2010, 19:07
now I'm going to go cry in my cornflakes:rolleyes:

safetypee
2nd Apr 2010, 23:44
piratepete, why should you think that something is wrong?
Not just because the 76 differs from the 75, which probably has a different brake heat pack and thus different energy capacity for a landing which itself has different energy characteristics (wt, speed).
If there is a difference between aircraft of the same type, wt, etc, then ask why. But all else being equal it might not be surprising to have hot, but not necessarily over-temp brakes in the conditions described.

Heed PA’s caution. Before ‘experimenting’ ensure that you consider the many issues involved in landing in such conditions.
As an example, reverse is more effective at high speed, thus use all of it early. With autobrake, the brakes carry more of the stopping burden at lower speed; if you require more brake before that, go to manual. See Figs 3 – 4. (http://flightsafety.org/files/alar_bn8-4-braking.pdf)

During a high energy landing, if you think that you can solve problems later, you will invariably be wrong.
Also, when using reverse and autobrake together you can get a false sense of the runway conditions. If the autobrake decel level is met by thrust reverse, then the brake demand is reduced; it is only when reverse is cancelled that a clear picture emerges – often too late. The principles are in flightops, flyingtechnique “Landing on Slippery Runways”. (http://www.smartcockpit.com)
The runway doesn’t have to be wet to have problems. At high altitude airports – dry atmosphere, there can be a significant dust covering which may reduce runway friction.

In addition to confirming that the required landing distance is available for the weight, check the margin from the maximum weight allowed. The margin gives an indication of how much braking will be required.
Aiming to use the full length near max landing wt is equivalent to giving up the landing distance safety margin (1.67 / 1.92) and thus the flexibility required to deal with the variability in normal landings. Thus you must approach and land at the correct speed, touchdown in the correct position, timely selection of reverse, spoilers, correct use of brakes, etc.

It only takes a small ‘experimental’ error to end up with soggy cereal – often found off the end of runways !

How to mitigate the ‘problem’ – don’t land downwind. In the extreme conditions described, tailwinds result in relatively much higher groundspeeds – hence high energy (V squared) – hot brakes.
Also, beware of wind measurement and reporting inaccuracies; even a small error (10%) in tailwind gives a significant difference in energy and stopping distance. IRS wind values are 'smoothed' - thus may not be sufficiently accurate for landing.
Landing into wind maximises the safety margin and minimises energy - heat into the brakes - economics.