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The situation that I came up with is merely hypothetical. Say a pilot was unable to land right after the runway threshold, for whatever reason it may be - a crosswind, etc - but was determined to land the aircraft.

I understand that most pilots would abort the landing and go around but say this one decides to land. However, it is too close to the end of the runway to stop just by using brakes, spoilers, and the thrust reversers. Could this type of landing (in an emergency) be achieved and by using the parking brakes what would happen if a pilot actually used the parking brakes to slow down?

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  • $\begingroup$ Not much besides wearing out the parking brake. $\endgroup$ – Joshua Oct 22 '15 at 3:25
  • $\begingroup$ On 747-100/200 aircraft there is no separate parking brake. To engage the brakes for purposes of parking, you depress the tops of the rudder pedals as you would for the usual wheel braking, then you pull and hold a lever that engages a hydraulic valve such that the pressure you're holding with the toe brakes is held, then you release the toe pressure you're holding. To release the brakes you, you depress the rudder pedal toes until the pressure you're exerting is greater than the pressure being held by the valve, at which time the vale releases and you're back to normal. $\endgroup$ – Terry Jul 10 '16 at 5:37
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This question appears to have an implicit assumption: that the parking brake would provide more deceleration than is available from normal braking. This is not generally the case.

A much greater worry for pilots than insufficient braking is actually excessive braking - to the point that the wheel locks up and skids. A skidding tire provides much less braking than a rolling one, and also quickly acquires a flat spot. Even on dry pavement, maximum braking would require an anti-skid system to remain effective; consider a 757 and a Mig-29, each of which blew out their tires when their anti-skid systems failed.

Note also that in small planes without complex braking systems, the parking brake merely maintains the pressure that is in the brake lines at the time it's applied. The parking brake would have no effect if the pilot were not already on the brakes, and would not be able to add any additional braking than the pilot could otherwise apply.

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  • $\begingroup$ Landing with the parking brake set is a recipe to destroy your tires pretty quickly, losing all ability to use your wheel brakes. I can't remember an aircraft where landing with the parking brake set was NOT prohibited. Nor can I think of one where the the "parking brake" was anything other than a way to keep the wheel brakes continuously applied -- not a separate brake at all. $\endgroup$ – Ralph J May 22 '15 at 3:03
  • $\begingroup$ I agree with this answer, however as mentioned in Dave's answer, there are some airplanes with abnormal/emergency procedures which actually use the parking brake as a backup system to normal braking, so it is used in some instances. As you say though, you will need more runway for this than with normal (antiskid) braking. $\endgroup$ – Lnafziger Jun 26 '15 at 17:45
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There is some nice info on this thread and it seems that the parking brakes on large airliners actuate the hydraulic systems as would be expected (unlike in some cars where the parking brake is its own mechanism). It also alludes to the fact that some emergency landing procedures would call for the use of the parking brake.

On a related note, it should be mentioned (and I don't know enough to know if this is actually possible in a large airliner) but I would think you would not want to lock the wheels to the point that they lost traction. This would actually reduce your braking ability.

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    $\begingroup$ Antilock brake systems actually were designed for use in aircraft first, and most large airliners and military aircraft have them. However, braking still heats up the tires which are already stressed from touchdown, so excessive braking can blow a tire. Wheel brakes also don't slow you down nearly fast enough in icy or wet conditions. Thrust reversers are typically used where available instead, though noise abatement policies might preclude their use in specific situations $\endgroup$ – KeithS May 21 '15 at 20:06
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Not quite the scenario you set up, but there was a case where a regional airliner landed with too much speed and too little braking effort. The pilot performed an unapproved and improvised action by applying the parking brake in an attempt to maximize braking. What he did not know was that by applying the parking brake, he deactivated the aircraft's anti-skid protection resulting in reduced braking effectiveness and an overrun down a steep slope.

As a general rule, tires work better at stopping a vehicle when they are rolling than when they are skidding because they generally have greater static friction (gripping) than dynamic friction (skidding). A parking brake is generally meant to keep a stationary vehicle from rolling away, not stopping one. Parking brakes may not be capable of generating enough force to do the job of stopping a vehicle or if they can generate the required force may not provide adequate control to avoid locking up one or more wheels in a skid.

I think the bottom line here is that if it hasn't been written into an aircraft's approved procedures, it's potentially a bad thing.

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  • $\begingroup$ Everything has greater static friction than dynamic friction; if the dynamic friction were greater than the static friction, the dynamic friction would keep it from moving even if enough force was applied to overcome the static friction - thus making the so-called higher dynamic friction actually, by definition, higher static friction. $\endgroup$ – Sean Apr 30 '18 at 17:19
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Actual RTO (rejected take off) is a certification test that airplane manufacturer must perform succesfully.

In this test the airplane must reach decision speed and abort take-off. When aborting take-off, the pilot should stop the airplane without using the thrust reverses and fire should not be extended to the airplane within 5 minutes (enough for passenguers to evacuate). This test shall be performed using the airplane at MTOW

So, your question addresses a lighter airplane (MLW < MTOW) and thrust reverses can be used. So the answer is yes, it can use the breaks and will work.

I provide you here the video showing the actual test performed by the A340.

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