Boeing 747-8 Being Put through some tough tests
The 747-8's certification rejected takeoff test: maximum weight, fully worn brakes, no reverse thrust, stopped on the runway.
A note on this page. The clip originally embedded here used a Flash player that no longer works anywhere. It has been replaced with Boeing’s own film of the 747-8’s rejected takeoff test — the most demanding single test in the certification programme.
Boeing accelerates a 747-8 to just above takeoff decision speed at maximum takeoff weight, then rejects the takeoff and brings it to a stop.
Why this test is brutal
The conditions are deliberately the worst that can be constructed:
- Maximum takeoff weight — nearly a million pounds.
- Fully worn brakes. Not new brakes. The test uses brakes worn to the limit at which an airline would be permitted to dispatch the aircraft.
- No reverse thrust. Reverse is not credited in certified stopping performance, so the test does not use it.
- No cooling. The aircraft must then sit for five minutes without the brakes being cooled, because in a real rejected takeoff the fire service takes time to arrive.
That last condition is the one that produces the famous images. The brakes absorb the entire kinetic energy of a 400-tonne aircraft at around 200 mph and convert it to heat. They glow. Tyres deflate through their fuse plugs, which are designed to melt and release pressure rather than let a tyre burst.
The requirement is that the aircraft stops within the runway distance, and that nothing catches fire for five minutes afterwards.
What it proves
Every rejected takeoff decision a crew ever makes rests on this test. When a captain aborts below V1, the performance figures say the aircraft will stop — and this is where those figures come from, demonstrated on the worst day the aircraft could plausibly have.
There is a detailed page on the 747-8 rejected takeoff test in the reference section.
The corollary matters just as much: above V1 the aircraft is committed to fly, because the stopping distance is no longer there. A crew that rejected 12 knots above V1 ran off the end of the runway.
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