Watching this video (at 06:58 mark), this plane had just made a mayday landing, due to a bird-strike. Because of the right engine being shutdown, it was forced to land immediately, with a full load of fuel. The added weight of the fuel, combined with loss of the additional stopping power of reverse thrust, caused the pilots to bear down on the brakes harder and longer than would be normal in an end-of-flight landing.

The pilot requests to hold on a taxi-way after vacating the runway, during which time the firemen come up to the plane to "inspect the brakes."

What do the firemen actually do when inspecting? Are they looking for fire? Glowing brake pads? Do they use an infra-red heat gauge?

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    $\begingroup$ Just a point of clarification, generally its not the actual brakes that catch on fire, but oils such as hydraulic fluid. The extreme heat can can lines to sever and dump oil onto the brakes. Hyd fluid burns around 2-3000 C. That's a bad day. For this reason, you don't set the parking brake after you stop with hot brakes because you will transfer the heat from the pads across the parking brake clamps and start burning things. The fire department comes out and actually measures the brake temperatures to ensure they aren't at dangerous levels and then cools them with fans. $\endgroup$ – Rhino Driver Jun 11 '15 at 1:46

There are specific protocols that procedurally are required to be followed. Insofar as brake inspection is concerned, it would have been obvious from the trucks that there was no brake fire. It's also obvious that there's not a major amount of smoke coming from the brakes. As they approached the landing gear, they would have smelled serious brake heating. Glowing brakes would be seen then if not sooner. A close visual inspection for very light smoke and sensing the heat coming off the brakes would give them an idea of the rate of brake vaporization. It's a subjective judgement based on what they see and feel.

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.

At a landing in Nandi, Fiji (short runway) with what turned out to be a tailwind in a 747-200 at near-max landing weight, we had to use max braking, and I called for huffers to cool things down, and of course for an inspection. I exited the aircraft as quickly as possible to see how bad things were. I was amazed and alarmed to see thick dark grey smoke pouring from the body and wing landing gear wheels. I thought we were close to having a fire. However, the ground personnel assured me that there was no cause for alarm, that the smoke was just brake vaporization that would shortly stop as they blew air on them. It did, and after refueling we departed without incident.

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    $\begingroup$ How did the passengers react when, after a touchy landing, the CO is the first to evacuate the plane? Serious question. $\endgroup$ – dotancohen Jul 22 '14 at 5:07
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    $\begingroup$ @dotancohen It was a freighter, so there were no pax, and it wasn't a matter of evacuating but rather exiting the airplane in the normal matter, which involved lowering a built-in ladder-like stairs in the floor of the upper deck down to the main cargo deck, and then out the airstairs that had been brought to the airplane as usual. Just as a matter of information, if a 747 lands at near-max landing weight at the end of a leg, it's most likely a freighter. Pax 747s rarely land anywhere near max-landing weight unless they're tankering fuel. $\endgroup$ – Terry Jul 22 '14 at 6:00
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    $\begingroup$ A young FO, aiming for Captain on Vulcans, was tasked to carry out high speed taxi checks. He bimbled (technical term) down the runway at somewhere around 100 kts, stopped and turned around for another run. 100kts back down the runway and a stop at the other end. Except it wasn't a stop. It was a boom, boom, boom as the fusible plugs melted and left a Vulcan up to it's axles in the grass having stopped about 20 metres short of the busy A15 road which ran perpendicular to the threshold of the runway. All the old hydraulic oil made quite a nice fire. He didn't make Captain. $\endgroup$ – Simon Jul 22 '14 at 7:28
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    $\begingroup$ @raptortech97 I really don't know the answer to that, except to say that air was what we always used. Thinking about it I would guess that the near-explosive generation of steam and shock cooling if you used water would cause problems. Air solves the problem without incurring further problems. $\endgroup$ – Terry Sep 9 '14 at 15:16
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    $\begingroup$ @raptortech97 I'm not a pilot, but from the physics perspective: 1. water could cool things too much, 2. it sprays and you don't see anything, 3. you have to carry the water, but you don't run out of air (a minor problem prbbly). $\endgroup$ – yo' Dec 18 '14 at 20:06

The firemen are looking for fire. If a blaze does break out, they will extinguish it.

I do not know the protocol for firemen using water to cool the brakes in absence of a visible fire. Also, it looks to me like the firemen are more interested in the right engine than the brakes.

  • $\begingroup$ you don't want to have the brakes catching fire at the gate while refueling $\endgroup$ – ratchet freak Jul 21 '14 at 15:22
  • $\begingroup$ @ratchetfreak I'm guessing you don't want to have the brakes catch fire, ever. $\endgroup$ – falstro Jul 21 '14 at 15:35
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    $\begingroup$ @falstro ratchetfreak's list of times at which you don't want the brakes catching fire was not exhaustive. :-) $\endgroup$ – David Richerby Jul 21 '14 at 15:48
  • $\begingroup$ but it's safer to have them catch fire on a out of the way taxiway than near the gate with all the ground crew $\endgroup$ – ratchet freak Jul 21 '14 at 16:07
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    $\begingroup$ They are checking the right engine too because it is damaged and fire could break out there if there was leaking fuel or oil. The fire may have been blown out by blowing air while they flew and might intensify when they stop, so it is also important to check. $\endgroup$ – Jan Hudec Jul 21 '14 at 19:10

Also there is a plug mounted on the wheel so if the brakes heat up the plug melts, so that the tire will not burst. This would be something they would also check.

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    $\begingroup$ Isn't that a matter of the tires heating up rather than the brakes? $\endgroup$ – Nate Eldredge Jul 22 '14 at 2:27
  • $\begingroup$ @NateEldredge: Well, the brakes can become really hot and the tires are close enough to get heated from them too. But there is not much to check there; if the plug melts, the tire deflates completely which is pretty obvious. $\endgroup$ – Jan Hudec Dec 19 '14 at 7:59

The tires are getting hot because of the huge amount of kinetic energy absorbed by the brakes. They also get a bit of heat from being used (friction from landing) but that's not very big: you can design a tire to take that: after all, your car tires don't get that hot from being driven on.

The brake assemblies act as heat sinks for the kinetic energy absorbed from braking: you have the whole brake assembly heating up to hundreds of degrees, even parts at 800-1,000 C. When you are moving, the air tends to stop the heat from going to the tires. And also to keep the brakes cooler by dissipating the heat. When you stop, the air isn't removing the heat, and radiant plus convective heat transfer from the brakes rapidly heat up the tires, causing the air pressure to increase. The plugs blow to prevent a uncontrolled burst. When you are moving there is no convective heat transfer, because of the air speed: as it heats it is replaced by fresh air. So there is only radiative heat transfer.

This is why tire plugs blow only when the plane is stopped, and the brakes are not being heated anymore by braking, but are actually starting to cool. The heat has to go SOMEWHERE after all, and without a constant stream of air, the tires suffer. After all, they are right next to this massive source of heat energy, at high temperatures. Is like being under a grill.

Some brakes have fans to help the cooling when the plane is stopped, but it's not a standard fit.

The landing gear is designed to prevent wheel burst (or fires) for enough time to allow the firemen to get there to either help cool the landing gear, or else extinguish any fires.

Cooling the brakes properly affects their longevity too: ideally you want them to cool slowly enough to even out any hot spots. Water cooling or even powerful fans can be problem because it can cool some parts too quickly: water mist is suggested.

If you look on the Airbus site, they have some very interesting documents for each plane: Aircraft Characteristics Airport and Maintenance Planning.

Airbus Aircraft Characteristics Airport and Maintenance Planning

There's a section that discusses what aircraft rescue and fire fighting should consider. One part discusses how they should deal with brake overheat and landing gear fire:

Hazard areas enter image description here


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