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Towing the airplane after an high speed abort

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Towing the airplane after an high speed abort

Old 10th Oct 2004, 11:15
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LEM
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Towing the airplane after an high speed abort

A colleague of mine, involved in the LIRN abort some time ago, vacated the runway and stopped.
He refused to move his 734 for more than one hour.
The airport authorities were quite upset because he "blocked" their taxiway instead of taxiing to the terminal.
We don't know exactly if the abort falled into the FUSE PLUG MELT ZONE.
Fact is, the tires didn't deflate, and he took off again after two hours.

Besides the excellent job he did in averting a major disaster (a collision with the Alitalia MD80), I raised the following point:

of course it's not possible to taxi on your own after that, but what about towing the airplane, at walking pace, watched carefully by the ground engineers, all the way down to the gate, instead of remaining stuck in a critical position for a small, crowded airport?
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Old 10th Oct 2004, 14:11
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HY LEM
A colleague of mine did taxi after a highspeed abort:the result ,all fuse plugs melt.
The temperature will continue to raise in the sidewalls of the tyres,if you continue to move the plane.As I remember,Boeing recommends to allow the wheels assembly to cooldown,before moving the plane.
"When in fuse plug melt zone,clear RWY immediately.Unless required,do not set parking brake.Do not approach gear or ATTEMPT TO TAXI for one hour.' from 737 QRH.
So ,my guess,your colleague did fine.
Brgds Alex
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Old 10th Oct 2004, 15:14
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You dont want engineers or other non essential people anywhere near the tyres so towing is probably not an option. If the fuse plug fails (by which I mean does NOT let the tyre deflate) then the tyre could explosively disassemble itself.
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Old 10th Oct 2004, 19:47
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You don't need to approach the main gear to tow the airplane, just the nose wheel, and I don't see the difference in heat transfer from the brakes to the rim itself in standing still or moving.

At the first sign of deflating they can always stop.

My scenario is the case in which you create serious problems to the airport in leaving the ac stuck where it is.

What about stopping in the middle of the runway and shutting down all engines?

The result, airport closes!

Anyways, that was just a guess as we all lack actual experience over this matter.

Thanks
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Old 10th Oct 2004, 21:30
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You don't need to approach the main gear to tow the airplane, just the nose wheel,
Any idea how far bits of metal will go if a tyre explodes? With a bit of googling the Aussie Govt reckons over 200 meters so I reckon you would still get perforated standing by the nose gear.

Air Safety Week in 8/7/2000 equated an aircraft tire explosion to the energy of 4 or 5 sticks of dynamite.

Below is from www.minesafe.org
A lesser-known danger arises when the combustion takes place inside the tyre, with no external signs. Whenever excess heat is developed in or applied to a tyre, it can initiate a process within the tyre known as pyrolysis - the decomposition of a substance by heat. This can cause a build-up of flammable gases and pressure within the tyre, which may ultimately rupture or explode.
Thus the installation of fuse plugs (and nitrogen fills). Of course the fuse plug may not operate properly and Kaboom.

As for blocking a taxiway and disrupting the airport, thats just tough. Its only money afterall, better that than killing someone.

Last edited by Daysleeper; 10th Oct 2004 at 21:42.
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Old 11th Oct 2004, 05:08
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Daysleeper,
"You dont want engineers or other non essential people" , since when did engineers become non essential....you cargo hauling tw@t.
Brgds
Doc


PS. The last bit was tounge in cheek
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Old 11th Oct 2004, 07:22
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My humble appologies doc. I shoould have realised that my comment was open for misinterpretation.

I meant that the fewer people near the aeroplane the better for their own safety. The only people near should be firefighters, properly equiped (helmets , thermal imagers etc), trained and paid to take risks.

NOT that engineers or any other members of staff are not important or indeed vital to the running of an airline.

Sorry.
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Old 11th Oct 2004, 07:25
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Safety first. No-one is arguing about that. There's a balance here between having the taxiway blocked for an hour to let things cool down by themselves or having it blocked for 5-6 hours to change wheels/brake assy etc if you try & taxi too soon. This isn't a simple decision and should be made after discussion by all parties, crew, engineers, Fire Service and airport management. I'd say if it's on a taxiway, not infringing the runway strip, then take your time reaching the decision. A blocked runway is more problematic. Thanks to those crews who think of vacating the runway and having the problem on a taxiway, wheel assemblies are certificated to take a lot of punishment. However, if you do need to stop on the runway and don't think it safe to move, so be it.

Our Fire Service have a neat bit of kit that saw action the other night. It's a large fan that forces cooling air over mainwheel assemblies for 10 mins or so, bringing them gently down to a safe temp for towing. MUCH better than squirting water over the wheels - a complete NO-NO!!

Wheel rims used to blow with monotonous regularity - was even part of our SOPs; what to do if you found a bit. Nowadays, as with tyres themselves, construction is much more reliable. I'd say 200 metres was possible, but the bits come out sideways, so nosewheel location is safer than the side. As has been said before. only Fire Service people should approach hot wheels/brakes in the first instance as they are (or should be!)wearing protective clothing and are trained to handle this situation.

If the runway is blocked, having made the a/c safe, towing off to outside the strip even on wheel rims shouldn't cause too much further damage. Do try and not smash too many light fittings on the way, though!!

The Odd One
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Old 12th Oct 2004, 10:29
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For aircraft with steel brake rotors, a high energy RTO generally solves the problem by itself - the rotors weld to the stators in a few minutes and discussions about the merits of taxiing become academic.

WRT the air blower for the brakes - that has been a standard bit of kit with my outfit for well over 25 years that I know of.
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Old 12th Oct 2004, 23:02
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... and I don't see the difference in heat transfer from the brakes to the rim itself in standing still or moving.
The heat transfer from the brakes to the rim may not vary but rolling the wheel will cause a heat increase. Perhaps this is the issue and the reason the aircraft should remain stationary.

Try driving your car for a bit on cold tyres. Come to a halt without the use of brakes, feel tryes. They're warm - rolling friction.
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Old 13th Oct 2004, 09:10
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Some years ago we used the air conditioning cart to help cooling down our brakes. I remember being impressed by the powerful airflow. Btw, apparently that didn't make any difference.... after half an hour the brakes still were hot he same. The B734 doesn't have temerature gauges on the brakes, so you can only guess by approaching your hand!...

Cpt Claret, I know, but I think rolling friction heat is negligible if you tow the airplane very slowly if compared to the hundreds degrees already accumulated.

My bet is it's worth a try, towing very slowly the airplane to a more suitable location, ready to stop at the first sign of deflation.
I think what has been done has already been done, rolling friction heat won't make any difference.

I say again, the scenario is not taxying the airplane under engine power, but towing it very very slowly, with passengers already offloaded.
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Old 13th Oct 2004, 12:51
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passengers already offloaded
nah, by the time you find a set of steps and a bus in the UK the brakes will be stone cold again.

Depending on the energy involved,
for the 757 BTMS reading of 5- 7 "caution range" Says delay take off and inspect again after 1 hour.

for 8 and above "Fuse plug melt zone"
clear runway immediately. Unless required do not set park brake. Do not attempt to taxi for 1 hour. Tire wheel and brake replacement may be required. (regardless of whether the plugs have melted or not)

To put it in context , for the 757-200 the Fuse plug zone starts at 30 million foot lbs of energy(per type A brake) .
Thats a max manual braking RTO at 116,000kgs from 140kts. on an ISA day.
If you have to do that you are almost certainly going to need an engineer anyhow to sort out whatever caused you to stop as well as check out the brakes etc.

I still say your chum at LIRN was in the right to sit for a while to let everything cool off. Though if there is no BTMS on the 734then I might have been getting an engineer to check the brakes etc out.
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