The rejected take-off test
Boeing aborted a take-off in a maximum-weight 747-8 Freighter on deliberately worn brakes, then left it standing to prove it would not catch fire.
The rejected take-off test is one of the most demanding things done to an airliner during certification, and it is deliberately staged at the worst possible moment.
What was done
In April, Boeing’s Test & Evaluation team took a 747-8 Freighter to a long runway in California. The aircraft was loaded to its maximum take-off weight, and its brakes were deliberately worn down to the limit at which an airline would still be permitted to dispatch it.
The crew then accelerated to the aircraft’s decision speed and aborted, bringing it to a stop using the brakes alone — no thrust reversers, because certification cannot assume they will work.
Why it is so severe
An abort at maximum weight and maximum speed converts an enormous quantity of kinetic energy into heat, almost all of it in the brakes. They glow, the tyres reach temperatures where their fuse plugs are designed to melt and deflate them deliberately, and the wheels can catch fire.
That is the second half of the test. After stopping, the aircraft must be left standing for a set period without fire crews intervening, to prove the fire will not spread. In service, this is the margin that gives an evacuation time to happen.
What it proves
Passing means the aircraft can survive the worst case an airline can legally present it with: heaviest, fastest, on the most worn brakes permitted. Not the aircraft as delivered — the aircraft on the last day before a brake change.
The 747-8 Freighter completed the test as part of a programme that also included extreme structural and systems testing before the type was certified.
Frequently asked questions
- What is a rejected take-off test?
- A certification test in which a fully loaded aircraft accelerates to its decision speed and then aborts, stopping on brakes alone. It proves the brakes can absorb the energy of a maximum-weight abort at the worst possible moment.
- Why are worn brakes used for the test?
- Because certification has to cover the worst legal case, not the best one. The brakes are worn to their permitted service limit, so the aircraft is proven at the point where an airline would still be allowed to dispatch it.
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