# Is there a way to calculate the braking distance for a light aircraft?

PPL student, I train in a C152. Reviewing its POH I cannot find a method to estimate brake performance roll (as I would do with T/O roll).

Is there any method or rule to calculate brake roll in smaller aircraft, such as C152?

I believe this could be useful to calculate a NO-GO point in the RWY in case of not achieving the expected take-off performance.

*Side note: For the lack of a better method, I would use LDG performance rolls in the POH. But I consider that this is a rough estimation.

• For the NO-GO point it's more useful to know what speed you should at some specific marker on the runway (like 500 ft or 1000 ft). Because on long runway if you take twice as much distance to get to rotation speed, you are not yet forced to abort to stop on the runway, but you already know your aircraft is underperforming and if you take off, the climb rate will probably be bad, so you should abort anyway. So for NO-GO point I suggest instead looking for way to derive it from the take-off distance required. Dec 17, 2021 at 17:06

You're overengineering this problem (at least for the sort of flying you're doing as a student PPL)

Even if you could calculate the exact stopping distance required with full brakes application, lets say for argument sake that is 200m, do you know the exact point on the runway where you safely have 200m to stop? What about all the things that could affect that number

• up/downslope
• deterioration of brakes due to age
• surface water/oil/other contaminants

Can you make or assume some sensible factor(s) to add for these conditions, and if you can and you now calculate the braking distance is 300m do you know that exact spot on the runway where you should make your call whether to continue your take off roll?

The way to do this without the overengineering is to follow the 70/50 rule. If you have not achieved 70% of your take off speed by half way down the runway then abort. Half way down your runway is easy enough to estimate.

• Thanks! Sorry if you felt I was overkilling it. Not at all. In fact, you can see that I am asking for either a method (with all its complexity) or a rule (simple 70/50 rule as you are pointing). Dec 17, 2021 at 14:59
• @ppinto no need to appologise at all. It's very easy to get super enthusiastic about these sort of things but the best thing to do is listen to your instructor and concentrate on learning the skills theyre teaching you. there's plenty of time to learn everything else as you progress on. Good luck with your PPL
– Jamiec
Dec 17, 2021 at 15:12
• If the runway has markings, their spacing is typically known, so you can tell the 300 m left point (300 m ~ 1000 ft, at that is usually the aim point wide bars for the opposite runway). Dec 17, 2021 at 16:55
• @JanHudec the 300 figure was a purely fictional figure pulled from thin air. Also, I dont know where the OP trains but a lot of smaller airfields dont have anything like the kind of markings of a large airport. Mine for example has a centreline, and numbers either end and thats about it!
– Jamiec
Dec 17, 2021 at 17:03
• Of course, if you have a 1500 ft or 2000 ft runway, you can't land 1000 ft down, so the marking will be different, and much sparser. But is there nothing at all to go by? Some cones on the sides or something that you could find out position of in advance and then reference your NO-GO point (abnormal acceleration detection point) to? Dec 17, 2021 at 17:18