When a pilot is abandoning a take-off, what are the effects on the aircraft performance? Can a pilot vacate the runway normally or is extra time on the runway needed? Is immediate assistance provided by the airport?
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3 Answers
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If an airplane is close to V1, the brakes - which have to absorb kinetic energy and dissipate heat - can get hot to the point where the tires automatically deflate, to prevent them from exploding. For a 747 this involves a lot of smoke and glowing brake disks.
answered Jan 24, 2018 at 11:56
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12$\begingroup$ Normally, though, (aborted takeoffs happen reasonably frequently wiithout disastrous results) the plane just needs to clear the runway have the brakes quickly inspected, wait a bit for them to cool down, and possibly top up fuel before attempting the next takeoff. $\endgroup$– J...Commented Jan 24, 2018 at 15:17
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7$\begingroup$ Note that the linked video was not a typical RTO, but was rather a test performed under worst-case conditions for certification purposes, including the use of completely worn brakes, a very high cut speed (200 mph!) and an aircraft loaded to MTOW. Also, this test may go quite a bit worse on an A340... $\endgroup$– reirabCommented Jan 24, 2018 at 21:25
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1$\begingroup$ Glowing hot brake discs in the vicinity of tens of tons of kersone combined with a risk of explosing. Sounds like somebody will also inform the firefighting department. $\endgroup$– florislaCommented Jan 24, 2019 at 13:56
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The outcome depends on the speed, aircraft, weight, and other factors.
If the takeoff is aborted at low speed (maybe up to 30-40kts), there may be no issues. The pilot would be able to vacate the runway and taxi back down to the end (assuming whatever caused the aborted takeoff is resolved).
Weights closer to the maximum takeoff weight or speeds closer to the maximum rejection speed (V1) would be major factors in making the situation more complicated. Both dramatically increase the amount of kinetic energy the aircraft must dissipate to slow down. At higher speeds, spoilers on the wings and thrust reversers on the engines can help. The rest is up to the brakes.
Some aircraft have brake temperature sensors that provide information to the pilots. They would not be able to take off again until the brakes cool down past a certain point, to ensure that if the aircraft has to abort the takeoff (again) they could safely stop the aircraft. Other aircraft may have a certain amount of time the pilots must wait. They should be able to taxi off the runway for this. The pilots may request assistance from fire crews to make sure there is no fire or to help cool the brakes. Some aircraft also have brake cooling fans.
If the wheel temperature exceeds a critical value, special fuse plugs will blow, allowing the tires to deflate. This prevents the tires from blowing out, which could cause damage or injuries. If the tires lock up during heavy braking, this can also cause the tires to blow out. If too many tires are blown or deflated, or the pilots otherwise feel they can't safely vacate, the aircraft could be disabled on the runway. The pilots would inform ATC, who would coordinate the assistance. If ATC notices smoke or flames, they will inform the pilots and may call for assistance as well. The fire crews will put out any fires and cool the brakes, and later the aircraft will have to be moved off the runway.
In order to be certified, aircraft must demonstrate that it can safely stop in "worst-case" conditions. This means that the thrust reversers are not used and the brakes are also at the most worn condition allowed. This puts the maximum amount of energy into the brakes while they are the least equipped to handle it. The tires may deflate but there cannot be any fire for 5 minutes to allow time for the fire trucks to arrive.
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$\begingroup$ V-1 is not, strictly-speaking, the maximum rejection speed. It is the maximum rejection speed for the specific case of a single engine failure during takeoff with no other damage resulting. There are plenty of failures that would require rejecting a takeoff even after V-1 (for instance, an elevator failure or two engines failing simultaneously). $\endgroup$– VikkiCommented Jan 19, 2019 at 4:32
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Depends upon the reasons for aborting the takeoff, how fast the aircraft is moving relative to V1, the amount of runway available to the aircraft, the response time of the flight crew to intervene and abort the takeoff, power settings used, etc.
Usually as part of the preflight process the crew will compute both the accelerate-stop and accelerate-go distances and brief them during the pre takeoff brief. An accelerate-stop distance is the distance required to accelerate the aircraft at takeoff power from a standaing start to V1, thence abort the takeoff and stop the aircraft using braking. Accelerate-go distance is the distance to accelerate the aircraft at takeoff power, continue to Vr, liftoff, and have a obstacle clearance of at least 35 feet at takeoff safety speed V2 if an engine failure occurs at V1. Provided the airport does not have a nonstandard obstacle clearance departure ie no obstacles in the departure path requiring steep climb gradients the crew will compute accelerate-stop distance and verify that there is enough runway available for this.
As to whether to abandon the aircraft on the runway or taxi off, depends on the nature of the emergency. Aircraft or engine fires or structural failures may require the crew to immediately abandon the aircraft once stopped on the runway. System malfunctions which don’t pose an immediate danger but require termination of flight operations ie. malfunctioning vacuum or pitot-static systems, etc. will permit an aircraft to taxi back to a parking ramp for shutdown and maintenance.
answered Jan 26, 2018 at 4:10