Question

[Yenn]

I frequent another site about flying called Boldmethod. It has questions and articles about flying safely.

 

The latest question is about brake failure.

 

If you are landing and you apply the brakes only to find they have failed, do you go around? Or words to that effect.

 

One of the answers on the site made me wonder what the capabilities of the pilot were.

 

 

[old man emu]

The answer to this is a very basic calculation of motion. Actually it is just the reverse of the GO/ABORT problem for takeoff. Let's look at the situation of an aircraft landing on a level, tar surfaced runway in Nil wind conditions.

 

First we have to work out how much time is spent in slowing from stall speed to stopped.

 

The equation is:

 

v^2 = u^2 + 2at

 

Where:

 

v = final velocity

 

u = intitial velocity

 

a = rate of acceleration

 

t = time during which the acceleration took place.

 

Since we are looking at a situation of slowing, the value of "a" is negative. Also "a" is usually taken to be acceleration due to Gravity in free air, 9.81 metres/second/second. However, this is reduced by friction when a vehicle is rolling on the ground surface. For a tricycle undercarriage on a level, tar coated runway, a suitable value for "a" would be (9.81 x 0.02 =0.1962). The figure, 0.02, is called the coefficient of friction, which I won't explain unless asked.

 

No let's say we are have a stall speed of 35 kts (40 mph 18 m/s) and there is no headwind, so ground speed = air speed. 

 

So how do we get to a value for "t"?

 

Using this equation:

 

 v = u +at   We can rearrange it so that

 

v - at = u

 

If we want the time to stop, then v  = 0

 

0 - at = u

 

-at = u

 

Rearranging for t:

 

t = u/(-a)

 

Since the airplane is slowing, "a" is negative

 

-(-a) = a

 

Therefore 

 

If u = 18, and a = (9.81 x .02) =0.1962

 

t = 18/0.1962

 

t = 91.75 seconds.

 

So now to calculate the distance to stop (d)

 

d = t. (u-v)/2

 

Since v is going to be 0 if the airplane stops, then

 

d = t.u/2

 

d = 91.75 x (18/2)

 

d = 91.75 x 9

 

d = 825 metres ( = 2700 feet)

 

The distance to slow from 35 kts ( 40mph) to 10 mph in the same conditions is 2050 feet. A speed of 10 mph should allow the aircraft to be turned off the runway.

 

The distance to slow to 10 mph in this case is dependent on the rolling friction, which is low on the runway surface, but much higher on the grassed edges of the runway. So, if the edges of the runway are suitable for running on, the idea would be to use the runway to lose some speed, then GENTLY steer onto the grass and run parallel to the runway.

 

These figures go to show that landing on dirt, gravel or grassed runways will result in shorter landing rolls, with or without brakes. Conversely, it's harder to get to flying speed from these surfaces.

 

 

[Student Pilot]

?

 

 

[jetjr]

Id not be able to work all that out in the few seconds decision time you had, by the time you worked out they weren't working could be too late anyway

 

If you had been a slow approach and everything going well, try to stop or run off somewhere safe

 

If things a bit fast, go around, think a bit and try again with more options prepared, grass etc is a good idea

 

Older Jabs not reknown for effective brakes, often loose performance on a hard brake/fast landing, not to be totally relied upon.

 

Pays to get good at slow approaches and have some options available for higher speed exit

 

 

[Yenn]

OME. I couldn't have said it better myself.

 

 

[Blueadventures]

If I decided not to go around; I'd stop my engine; as prop at idle will maintain velocity.

 

I have experienced minimal brake pressure on downwind.  Decided to land as if no brakes and see how long the ground roll is.  I set up for a slow safe final, after landing and then when about a third along the 700 meter sealed airstrip it was not slowing; so I turned the engine off and it started slowing to a stop.  Came to a halt with about 100 meters to spare.

 

It go to know how much effect an idle engine has at 45 - 50 kts.

 

I'm not an instructor just passing on an experience I had for what is worth.  Cheers

 

 

[facthunter]

I won't live long enough to work out if OME is right or not.. Logically IF you KNOW the brakes are U/S you would do a somewhat different approach to a normal one and perhaps land in the grass into wind and touch down with as much  roll length available and as slow as possible. and have space to gently ground loop it at the end of the roll if a wire fence is coming up or roll up a hill.

 

  Yes you might as well cut the engine when you are certain you won't need it and turn fuel and electrics off.. You won't have your radio  but can attend to that when you have stopped safely.Nev

 

 

[Thruster88]

When landing without brakes this method will get the friction required to stop on the runway.

 

 

 

[alf jessup]

When landing without brakes this method will get the friction required to stop on the runway.

 

 

X Navy pilot me thinks, carrier landing that one so just smack it on.

 

 

[Litespeed]

This is one of the areas where OME has done a great explanation of what actually is needed from the basic maths. We need to always have this in our minds, a bit of knowledge of how the physics will work out. That leads to a simple basic rule of thumb to apply a solution to.

 

We don't need to have the equation running, when we encounter the problem- just a understanding that the distance will be surprisingly long unless we do differently.

 

Naturally real world experience shows he is right. A basic physics understanding is golden when it just becomes intuitive, it leads to sound decision making.

 

 

[old man emu]

This is one of the areas where OME has done a great explanation

 

Thank you for the complement.

 

 

[facthunter]

The twin that flopped on the runway was so slow it just didn't flare. A lot of them have laminar flow wing profiles that just stop lifting rather quickly. He's pretty lucky to survive that episode.. IF one wing had dropped a bit  it would be another story. It looked like he was doing it flapless.  It looked FAST on approach and I can't see any flap extended. Nev

 

 

[kgwilson]

I frequent another site about flying called Boldmethod. It has questions and articles about flying safely.

 

The latest question is about brake failure.

 

If you are landing and you apply the brakes only to find they have failed, do you go around? Or words to that effect.

 

One of the answers on the site made me wonder what the capabilities of the pilot were.

 

I checked this out too and I thought that their responses were a bit convoluted although reasonable. The "Declare an emergency with ATC" option assumes you are at a controlled aerodrome and I don't know any that have runways that are so short a single engined aircraft could not land 2 to 3 times in its length.

 

To me it is just simple.

 

1. If you can choose the grass
    
   
2. Cut the engine when you know you will make it & try to touch down as close to the theshold as possible deadstick. 
    
   
3. Decide early if you are slowing enough & start & go around if you are not.
    
   
4. Repeat 1-3 but get it right this time.
    
   

 

I lost the right brake in a 152 when I was training on a cross county exercise & my downwind check was a bit ho hum. On rollout (grass) I nearly ended up in the ditch but the rudder still had a bit of authority & was lucky. A top up with brake fluid & a bleed fixed it for the flight home.

 

 

[old man emu]

To me it is just simple.

 

1. If you can choose the grass
    
   
2. Cut the engine when you know you will make it & try to touch down as close to the theshold as possible deadstick. 
    
   
3. Decide early if you are slowing enough & start & go around if you are not.
    
   

1. The grass, or even dirt/gravel provide higher rolling resistance than a sealed runway, but stay off the grass if it is damp.

 

2. If the engine is idling, it is still producing a modicum of Thrust.  How far will your plane roll at engine idle?

 

3. If you do 2, you can't do 3. Once you do 2 you are committed to the landing, just like a glider.

 

The worst case scenario would be to find out the brakes don't work at that point in the landing roll where the ground speed is low enough to use the brakes as you would in an uneventful landing.

 

What I didn't add to the calculation was "Reaction Time" which is the time between when you start to apply the brakes as normal, find the plane isn't slowing, recognise the cause, then implement you previously developed plan.

 

I suppose it should be part of training to have yourself develop a plan to deal with misfortunes during landing, not just bouncing or wheel-barrowing. You couldn't practice a tyre blow out, but I suppose you could easily simulate brake failure during a sessions of circuits and bumps.

 

 

[Yenn]

Checking your brakes as part of the pre landing checks, only tells you they are working then. They probably worked last time they were used, so what is the likelihood of them showing failure and isn't it the same as the chance of them failing even if they checked OK on downwind.

 

I wouldn't know if my brakes are working or not, until I have used quite a bit of runway. I am not too keen to apply them at high speed and risk the tail coming up.

 

 

[Blueadventures]

I was taught first check on down wind is Brakes for pressure, then undercarriage down etc.  On my occasion it alerted me early. so beneficial.  I do;'t know how many don't do that or were taught that. Cheers.

 

 

[kgwilson]

1. The grass, or even dirt/gravel provide higher rolling resistance than a sealed runway, but stay off the grass if it is damp.

 

2. If the engine is idling, it is still producing a modicum of Thrust.  How far will your plane roll at engine idle?

 

3. If you do 2, you can't do 3. Once you do 2 you are committed to the landing, just like a glider.

 

I've done plenty of deadstick landings, restarted and taken off again so yes if you do 2 you can still do 3.

 

 

[Thruster88]

The Thruster has no brakes and I like it that way, makes one a better pilot perhaps. The stopping distance from 35kts is only about 1/4 of  OME's  calculations.  

 

 

[old man emu]

I've done plenty of deadstick landings, restarted and taken off again so yes if you do 2 you can still do 3.

 

It affects the situation if you are planning to do a deadstick followed by startup and take off. You have already prepared yourself for the tasks you must do to restart and takeoff. What I think we are talking about is the sudden realisation after landing that the brakes have failed. There could be up to 5 seconds or more lost in identifying the problem and activating a recovery plan. At 18 m/s you travel 90 metres of 295 feet. And that's if you have previously considered the situation and formulated a plan before you even go near a plane.

 

One good thing about Yenn's original post is that it has got people thinking about developing a plan to deal with this situation.

 

 

[kgwilson]

If you have good brake pressure when doing downwind checks the risk of failure on landing is very small so if you have no pressure on down wind you have plenty of time to plan. If you don't check & do a deadstick, find no brakes the reaction time will be a bit longer but a restart is the first choice always & then going around you can sort it out. 

 

 

[pmccarthy]

My downwind check with BUMFISCH has always been to check that the brakes are OFF, not whether they work.

 

 

[turboplanner]

My downwind check with BUMFISCH has always been to check that the brakes are OFF, not whether they work.

 

Someone didn’t teach you the full detail; “Brakes OFF and operating.”

 

(Hydraulic test)

 

 

[facthunter]

Just HOW do you check they are operating? You find that out when you apply them and it goes off to one side or doesn't work at all. Nev

 

 

[turboplanner]

 A quick pull on the lever while ensuring the park lock is off.

 

 

[facthunter]

I have no idea what you mean. Nev