Aborted Takeoff?

Question

Me and my roommates were having a heated debate about the dangers of an aborted takeoff in an airliner after reaching V1. I feel the main danger is the lack of runway after reaching V1 and the possibility of fire in landing gear from heated brake pads. One of them is saying that because of hard and excessive application of brake, the Hydraulic system operating the brakes will explode and so will the hydraulic shock absorption system. I beg to differ. He also claims that the white smoke coming from landing gears during landing is actually the vaporised hydraulic fluid being released from the system due to high pressure. I am a mechanical engineer and do not know the details abt aircraft's systems but from the basics I learned as an engineer, I find it hard to accept. Please enlighten

Answer 1

the smoke is rubber from the tyres burned. the hydraulic systems are not open-designed but sealed. they do not eject any fluid.

aviophage summarized the rejection decision well.

Answer 2

well, im not engineer, but i think the smoke on landing is the tires   burning the rubber as they touchdown. they accellerate from 0 to whatever your airspeed is in fractions of a second. Andthere is a lot of stress on the braking system from aborting a takeoff at v1, but if you are having to abort, do you really have any other choice but to brake?

Answer 3

Rarely is it the case that lack of remaining runway is available to stop after V1. Our exec 727 on a coast to coast flight will balance out between 5500-6500 feet and other than the occasional 7000 foot runway we rarely must condend with less than 9000 and more often than that more. The only discussion about legality is contained in PT 91 and that does not discuss weather or not you CAN abort after V1. In fact, you can move V1 anywhere you want so long as it is not below VMcg or above Vr. Either would require recalculation of the BFL since the runway needed to stop and that needed to continue would no longer be equal or balanced but it is perfectly legal to do so. For instance, it would make sense to have a very slow abort speed on an icy runway wouldn't it. Likewise, if the runway is long enough.you could simply make V1 equal to Vr. That is what we do in our operation because we believe a rejected takeoff should be avoided at all costs. More on that below.

The latest consensus among airlines and manufacturers is that refected takeoffs are simply dangerous for many reasons I won't go into here. A study of go's and no go's was completed several years ago.  I don't recall all the data precisely but about a hundred each rejected takeoffs and another hundred takeoffs with sever malfunctions at or near V1 were looked at. They tried to gather similiar situations where previously held conclusions on the subject would not have produced such things as "he should have" or "he should not have" monday morning quarterbacking as all of the events were handled in a way that were correct at the time about aborts near V1. 65% of the aborts resulted in further damage or loss of the airplane while not one decision to continue the takeoff did not result in a safe return for landing with no further damage. So as I said before. In our operation if we have enough runway and the surface is not contaminated, we don't even have a V1. And if we do, there would have to be reason for me to suspect that the airplane is not structurally capable of flying for me to abort.after 80 kts as Charles mentioned above. That simply means loss of control, engine fire or failure.

This is a very interesting subject and if enough people are interested I'd be happy to discuss it sometime in conference on messenger or wherever. Takeoff and landing performance in transport category aircraft has allways been a passion of mine and I don't just mean the numbers but what went into those numbers.

Answer 4

V1 is calculated before every takeoff (or should be) based on runway length, wind conditions and surface conditions.

If burning brake pads / running out of runway occurs, V1 was miscalculated.

It's designed to take these things into consideration.

Smoke from the tyres, I'm pretty sure is vapourised rubber. Same as spinning the wheels on a car with the front brakes engaged.

Answer 5

you are right. that is how one should do. I agree

Answer 6

If they abort the take off theres going to be a reason for it and more often than not it will be unavoidable. As much as it may damage the breaking system its much better than not having sufficient power and having the possibility of a collision or crash due to unresponsive controls.

Answer 7

Do we really need an explanation  if you abort after v1....Once you hit v1 your done, you go with the takeoff, that's the whole reason behind it.  Try to abort after v1 at Chicago-Midway, wouldn't be a pretty sight...

Answer 8

The smoke on landing is rubber being burned. On many runway touchdown zones you can see the runway completely coated in this rubber.

For a multi-engine aircraft to be legal to takeoff from a runway, something called balanced field lenght is calculated. This lenght makes certain that the aircraft can accelerate to V1, and apply full braking and stop within that lenght. If your balanced field lenght is 5,000ft you can operate from runways from 5,000ft upwards.

Many Pilots will limit the things they abort there takeoffs to above 80 knots. For example most guys will only stop above 80 knots for control, instrumentation or engine problems and not a burst tire or open cargo door.

And aborted landings are covered during testing. If a brake catches fire the tire has fuse plugs which prevent the tire from exploding. And the newer Carbon Brakes manage heat much more efficiently.

EDIT: No. Aircraft brakes arent that diffrent from those in your car. Why should there be a buildup in pressure??? Heat is the biggest issue.

Answer 9

What can I say?  The hydraulic systems are designed by engineers!  You get what you pay for, right?   :=)

Certainly in my experience with Boeing airplanes, the systems are well designed and rugged as a lighter knot.  Why would pushing on the brake pedals harder cause the system to explode?  If that were true, then I could blow myself to h**l sitting on the ramp, just by standing on the brake pedals really hard.

So I think you are right and the other guy is wrong.

Also, I really like what John B says above.  Aborted takeoffs are to be avoided at all costs.  If in doubt about the balanced field length, do what you have to do about loading.  I'd rather be on the carpet for refusing a load or doubling a trip than risk sticking it in the mud and ripping the mains off.

Right?