FlyerTalk Forums - What happens after a runway incursion during takeoff?

Quote:

Originally Posted by ijgordon (Post 18928846)

Obviously, in this case, it was UA's fault. ;)

I'm curious how long the brakes take to cool down after a normal landing. Obviously there's time built into the schedule for the turnaround. If Southwest does 30-minute turnarounds, plus maybe 10-20 minutes of taxiing at each end that implies at most about 60 minutes but possibly much less. Just curious how much harder the brakes work in an emergency situation compared to business-as-usual.

Airliner brakes are called multiple disc brakes, a car has a single rotor with a caliper that has the brake pads attached that apply pressure to the rotor to create the braking action. On an airplane, there are multiple rotors, and between each rotor there is a stationary disc called a stator, hydraulic pressure is applied and compresses the rotor/stator stack together creating the braking force.

A large amount of heat is generated by the friction of the rotors against the stators, in normal brake applications there is enough of a mass that the heat is absorbed and during normal turnarounds the heat dissipates enough so the airplane can taxi out and take off for the next flight.

In a rejected take off or RTO, the brakes are used to their maximum and so much heat is generated that the brakes must be cooled down to a certain temperature before the next take off. A majority of the brake assembly is inside of the inner wheel half of the tire assembly and is not really open to normal cooling air, that is why they will put fans on the brakes to cool them down.

Airplane tires are tubeless and are inflated to over 150 psi, so in order to prevent a hot brake assembly from overheating the tires and possibly causing an explosion, the wheel assemblies have internal thermal fuses, or plugs that are designed to melt at about 350 degrees and release the air in the tire, the main reason is to prevent a tire from exploding in case of a brake fire caused by an overheated brake.

So besides waiting for the brakes to cool down, the brakes must be inspected for signs of heat damage and to make sure the thermal plugs did not melt or deform.

Here is a link to a video showing a rejected takeoff during certification of the Boeing 777, as you can see in the later part of the video, the brakes get so hot they turn cherry red and start to burn, and as a result the thermal plugs in the wheels melted and the tires deflated. All airplanes must go through this rejected takeoff tests as part of their certification process.

http://www.youtube.com/watch?v=wXpjBxD0Rhg

While this test is to the maximum extreme that will probably never be encountered in normal airline service, it does demonstrate part of what an airliner has to go through to be certified.

Mr. Elliott