Why don't aircraft have brake lights so you can see when an aircraft in front is slowing down?

I know there are air traffic controllers to control aircraft but they cannot do much about an aircraft's speed on the ground, it is down to the pilot.

  • 3
    $\begingroup$ Question in reverse: why aren't there Navigation lights on automobiles. The reasons are the same : "To avoid collisions" $\endgroup$
    – Mazura
    Jan 20 '18 at 0:17
  • $\begingroup$ @Mazura Brake lights are so other vehicles know that you're about to slow down or stop, possibly very quickly. Headlights, tail lights, and parking lights are the road vehicle equivalents of navigation lights. Turn signals, brake lights, and backup lights don't really have equivalents on aircraft because they're generally not needed. Airplanes don't taxi quickly, nor do they stop or turn quickly while taxiing. Also, most aircraft moving on the taxiways are in radio communication with each other, so they frequently already know each other's intentions. $\endgroup$
    – reirab
    Jan 20 '18 at 6:42
  • $\begingroup$ Four words, not an answer because it would be a circular argument: steering via differential braking. $\endgroup$
    – user
    Jan 20 '18 at 18:59
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    $\begingroup$ 'cause where we are going, there are no roads. $\endgroup$
    – motoDrizzt
    Jan 21 '18 at 7:25

They simply aren't necessary.

Brake lights are on road vehicles because often they travel at relatively high speeds, and follow relatively close to one another. If a driver suddenly slows, the brake lights help provide a visual cue (which grabs the attention of other drivers, and is visible from quite a long distance) that the vehicle intends to slow or stop.

In aviation, no aircraft should be traveling on the ground (taxiing) at such a velocity that stopping in a short distance is a problem - nor should they be following another aircraft too closely (regulations/airport rules govern both taxi speed and following distances). Taxiing aircraft are either in communication with an air traffic controller, or each other, making the need for sudden stops, change in speed or direction highly unusual. In addition, there is a higher degree of professionalism within the aviation community than your ordinary automobile driver; pilots pay closer attention to what their and other aircraft are doing; i.e., you won't find a pilot with a Big-Gulp in one hand, a shaving razor in the other, head facing the back seat passengers, all while attempting to pilot the aircraft!

In short, brake lights wouldn't be necessary on road vehicles either under the same conditions - but as it is, they assist in preventing collisions in numerous situations. In aviation, these sorts of collisions do not occur often due to the factors above, and therefore are not necessary.

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    $\begingroup$ I would dispute the last paragraph, but +1 for the first part. The stopping distance of a car is much, much, much, shorter than that of an aircraft. The speed limit on the highways near where I live are faster than the speed at which I land, but I can stop from that speed far more quickly in my car and the car behind me will be much closer. If I suddenly need to stop immediately (say, a deer suddenly decides that the highway would be a great place to stand,) the car behind me will have a fraction of a second to respond to keep from hitting me, even without distraction. $\endgroup$
    – reirab
    Jan 19 '18 at 23:19
  • $\begingroup$ @reirab I don't think brake lights would have any effect for landing aircraft... you just can't stop from those speeds, as you mentioned, and ATC should be in control of any runway incursions as well as landing planes are required to determine if the runway is safe to land on (the professionalism thing again, much more-so than automobile drivers). I think OP was asking more-or-less about taxiing aircraft, which is a case where brake lights would be more applicable, but still not necessary. $\endgroup$
    – SnakeDoc
    Jan 19 '18 at 23:42
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    $\begingroup$ Oh, I completely agree that they'd be useless on an aircraft. It was the "brake lights aren't necessary on road vehicles either" that I would dispute. Road vehicles have sub-second reaction time requirements in many cases. Brake lights very much are necessary on road vehicles, especially when driving on highways in heavy traffic, even disregarding people who aren't paying attention or speeders. $\endgroup$
    – reirab
    Jan 19 '18 at 23:48
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    $\begingroup$ @reirab Oh I see, perhaps it's better said: "brake lights on road vehicles wouldn't be necessary under the same conditions..." $\endgroup$
    – SnakeDoc
    Jan 19 '18 at 23:51
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    $\begingroup$ @LieRyan No, taxiing aircraft have those speed limits because they're much less maneuverable than cars and can't stop nearly as quickly. Aircraft are not designed for cornering like cars are. Try to take a turn at 45 mph (let alone 80 mph) in an airplane and you'll have a wingtip on the ground. $\endgroup$
    – reirab
    Jan 20 '18 at 6:28

Brake lights are pointless on aircraft because aircraft cannot make fast stops (at least without arresting cables like on aircraft carriers).

Brake lights signal that ground vehicles ahead maybe making fast stops. Following cars can then make their own fast stops based on driver evaluation of distance etc.

Aircraft inability to make fast stops is by necessities of the landing process. Too sudden braking while landing could flip or otherwise cause loss of directional control. Remember not all wheels are necessarily touching ground, especially with bouncing and wind gusts. One wheel braking leads to non-Zen results. Plus too firm a stopping action will blow out aircraft tires. Worse there really is not any feedback on braking until tires hit landing strip final time evenly on all wheels and then its too late. So airplane designers remove the landing time hazard by reducing normal braking available (which also reduces weight of brakes and saves fuel/money). Of course the same brakes are in use on taxiways, making slow movement wise.

Furthermore unlike cars, aircraft brakes rely on getting some cooling effects during extended braking. Landing brakes are optimized for much heavier braking by spreading braking over longer time and distance -- remember plane braking starts at speeds 200-75 mph depending aircraft and much heavier plane weight for wheel size etc.

Brakes on ordinary cars will not melt even during emergency braking. And though tire blow outs are possible, the consequences are generally less than aircraft when each starts at ordinary speeds. Semi and race cars are a bit more like aircraft and do not stop as fast without consequences).

Also remember most ground collisions are not rear-end accidents within steadily moving traffic. The vast majority of collisions are due to wrong turns at incorrect intersections into lines of traffic or even onto active runways which are not even looking for that intersection to be in use. Brake lights would not help as nobody is behind colliding planes.

(Ground control normally uses very few of airports possible taxiway turn points on any given day -- fewer = simpler.)

Where rear-end collisions do happen its almost always the same as cars at a stop light that just changed. Usually no time for brake lights to come on or plane behind to react -- once the guy behind guns it way too fast for the conditions (and usually regulations). Usually the guy in front simply does not accelerate as much or as long as expected by the guy behind -- front plane brake lights never would have come on in time even if equipped. Similarly sometimes fog is a factor that makes allowable acceleration hard to judge. But like with cars, fog also tends to negate the value of brake lights except to confirm what you hit was not a building.

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    $\begingroup$ I'm not convinced that "fast stops" is part of the story here. Sure, the plane in front of you may not be able to stop quickly, but in that case neither are you, so the reaction time you need to avoid ramming him is the same. I would much rather believe an explanation that says planes taxi with enough distance between them that you have time to notice directly that the guy in front of you is slowing down before you engage your own brakes. $\endgroup$ Jan 20 '18 at 13:54

Pilots are required to taxi at a speed consistent with being able to stop safely and are generally taxiing in trail so are not going to run into one another. Most commercial airliners also have maximum straightline and turning seeds defined by their operators. As these are generally the same - planes are not going to run into each other.

Most accidents (usually wingtip touches) occur when pilots in a rush cut corners instead of staying on the designated taxi line - and so wingtip clearances are lost - on in the generally unmarked non-movement area (where planes DO move - just not under ground control) and pilots are maneuvering to make gates or depart among the jetways, tugs, baggage carts and the like which are SUPPOSED to be moved out the way.


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