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In this question, our intrepid former 747 pilot Terry mentioned, in the accepted answer, that:

As I understand it, tires that dangerously overheat will explode before melting, and that's why thermal plugs are used which melt and deflate the tire to prevent their exploding.

His understanding was confirmed by other comments and answers.

My question is what is the net difference between a tire deflating due to the plug melting and the tire deflating due to explosion? Either way, you're landing/taxiing with a flat tire.

The only thing that comes to mind is that once the plane is on the ground and stopped, an exploding tire might injure safety crews and/or pax evacuating.

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  • $\begingroup$ All three of the answers provided (so far) are very useful. How do I go about selecting one to mark as the answer? $\endgroup$ – FreeMan Dec 18 '14 at 16:13
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    $\begingroup$ Click the "tick" icon next to the answer you want to accept. If you're asking how to decide which answer to accept, you should choose the one that you felt best answered the question, which is entirely subjective. Also, I'd recommend waiting a while. You only asked your question a couple of hours ago: maybe the most useful answer hasn't been written yet. Or maybe the community's votes will help to guide you. $\endgroup$ – David Richerby Dec 18 '14 at 16:40
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    $\begingroup$ As I understand it (and was taught in ground schools) the most likely scenario involving a fuse plug melting and deflating a tire, at least for a 747-100 or -200, would not happen during the actual landing or taxiing. It would occur sometime after landing and taxing to parking, when the energy in the overheated brakes has time to transfer to the tires. $\endgroup$ – Terry Dec 18 '14 at 19:43
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    $\begingroup$ @DavidRicherby yes, I'm aware of how to mark an answer, I was wondering which one to choose... Since it is close to Christmas and most folks are busy shopping, I was hoping someone might volunteer some cash to have their answer selected. ;) $\endgroup$ – FreeMan Dec 19 '14 at 13:52
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An exploding tire while the plane is rolling will propel debris in various directions.

This happened with the crashed Concorde on takeoff. A chunk of the tire hit the tanks and caused a punctured in it. This then lead to the fire and loss of power.

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    $\begingroup$ The chunk was not from a tire, but from a badly maintained US airliner which had taken off from that runway shortly before. It destroyed the tire AND the wing when it was run over by the Concorde. $\endgroup$ – Peter Kämpf Dec 18 '14 at 14:11
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    $\begingroup$ @PeterKämpf the debris ruptured the tire and chunks of the tire were propelled into the wing according to the official reports. $\endgroup$ – ratchet freak Dec 18 '14 at 14:12
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    $\begingroup$ Interesting, I hadn't considered an explosion on a take off run. Two issues on applying this answer to my original question: 1) take off speed of the Concorde is much higher than most other aircraft, exacerbating the flying debris issue, 2) a melt plug wouldn't have had any impact on the Concorde crash, since the tire exploded due to physical damage, not heat. $\endgroup$ – FreeMan Dec 18 '14 at 14:18
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    $\begingroup$ @FreeMan a truck tire exploding could take off your head and truck tires have lower pressure than aircraft tires and go slower than an aircraft on takeoff. $\endgroup$ – ratchet freak Dec 18 '14 at 15:25
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    $\begingroup$ @FreeMan It's true that a melt plug wouldn't have helped in the Concorde incident. I think he just gave that example to show the dangers of an exploding tire. Also, while you're right that the Concorde takeoff speed was higher than normal, that would only have mattered if the tire exploded within the last couple of seconds of the roll. At any rate, I'd assume that most of the kinetic energy of the pieces of the tire came from the explosion rather than from the rolling speed of the tire. $\endgroup$ – reirab Dec 18 '14 at 15:37
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An explosion creates debris

For aircraft, Foreign Object Damage is a big concern and an exploding tire would be a major source of FOD. This would be a concern to the landing aircraft itself as its engines might suck in the debris of a blown tire, and it would be a concern to other aircraft as tire fragments can be blown all over the runway and might in turn be ingested by the next aircraft landing or taking off.

An explosion might damage the aircraft

Aircraft tires are inflated to very big pressures so the explosion itself or the speed of the fragments might be enough to cause severe damage to the aircraft systems or fuselage.

Explosions are dangerous to people around the aircraft

If an aircraft lands at speeds that could cause the tires or brakes to overheat, firefighters will inspect the brakes and tires of aircraft that have landed and might have overheated the tires or brakes. With thermal plugs the pressure in an overheated tire will be vented in a controlled fashion (the firefighters can predict the direction of the vent) so it's less of a safety issue.

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    $\begingroup$ This answer contains real data on tire pressures. $\endgroup$ – Peter Kämpf Dec 18 '14 at 14:12
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    $\begingroup$ There are also hydraulic and electrical lines inside the wheel wells that can be damaged in a tire explosion. The primary of the the Travis Barker Learjet crash was rejecting a takeoff past V1 after the tire blew. It was made worse because debris from the tire damaged the squat switch, causing the thrust reversers to retract. Although the tire explosion was caused by under-inflation, a similar accident could happen with hot tires. $\endgroup$ – Brian Dec 18 '14 at 16:04
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You are right that a main reason for fuse plugs is safety of people nearby.

Surrounding structure is generally reinforced to protect against tires bursting, but if it bursts while stationary it can cause damage and will send debris in a different pattern than it would if it were moving (which is when tires usually burst).

It also relates to fire safety. An exploding tire can spread burning liquid or debris.

Tires spend most of the flight inside the wheel well. Under normal conditions, brakes will be hottest after landing, and would be allowed to cool down after a rejected takeoff, so the tires should not be excessively hot when retracted. Systems and structure in the wheel well is reinforced, but fires are possible, and an exploding tire in the wheel well can certainly cause damage.

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  • $\begingroup$ How often do tires explode in the wheel well during flight? Or is that a whole new question? $\endgroup$ – FreeMan Dec 18 '14 at 18:21
  • $\begingroup$ @FreeMan it's not really common, but something to consider. I am editing to make that more clear. $\endgroup$ – fooot Dec 18 '14 at 18:28
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An exploded tire cannot be reused. A deflated tire, after relevant inspections, can be reused.

Yes, you will need a new fusible plug but that is a lot less expensive than a new tire.

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  • $\begingroup$ Compared to the points in the other two answers, this seems very minor, however it is still quite valid. $\endgroup$ – FreeMan Dec 18 '14 at 16:10
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    $\begingroup$ I hope they didn't reuse the tire from the Concorde $\endgroup$ – rbp Dec 18 '14 at 16:12
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An exploding tyre throws heavy tyre fragments in all directions at high speeds. Fragments might damage the plane but they also might kill anybody nearby, such as emergency services personnel, ground crew and passengers.

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One other consideration not yet mentioned.

Aircraft tyres are highly pressurised. An exploding tyre will throw debris in unpredictable directions.

In the case of a brake or other undercarriage fire, the firefighters are trained to approach the fire from the front or behind since the fusible plugs are designed to rupture and vent the pressure sideways.

Also, a fire in the wheels weakens the alloy. If the tyre explodes, then sometimes the wheel explodes too and hot pieces of metal zooming around are even worse than the rubber.

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