The high cost of heavy braking
 

Back In the 1960’s, the Douglas Aircraft company published a flight safety newsletter that included an article titled The Hard Cost of Heavy Braking. It quantified the cost in dollar terms, of wear and tear on tyres per landing. While frequency of landings was an obvious factor, pilot braking technique was the main culprit affecting cost.

Having retired from flying Boeing 737’s for most of my airline career I was recently offered a flight in an Airbus A320 simulator. It was the first time I had been in that aircraft type. The instructor was very patient with me both in the pre-flight briefing and the simulator. He let me fly the simulator while he did all the setting up using the FMC where required

For landing we used an 8000 ft sea level runway and no wind. My touch down was just average and as I was about to shift my feet up on the rudder pedals to apply the brakes, the autobrakes cut in and we pulled up quite quickly. It caught me by surprise as I had expected to use the brakes manually. I queried this during the post flight de-brief only to be told the company used auto-brakes for all landings regardless of runway length.

During the ten years I served with one Pacific island operator flying the Boeing 737-200, it was left to the captain to decide whether or not autobrakes were used for operational reasons. Our runways varied between 5000 ft to 10,000ft in length with the surface either coral based or normal hard surface. Being near the equator, heavy rainfall making runways slippery was an occasional hazard.

Auto braking was very rarely used unless operationally necessary. Accurate airspeed control and point of touch down was the key to good landings without having to use heavy braking. From the company point of view, cost of brake wear and tear was never a factor in a decision to use manual or autobrakes. As it should be of course.

Since then I have flown the 737 with several other companies who mandate the use of autobrakes for every landing - regardless of runway length or whether operationally necessary. When I read the 1960's Douglas Aircraft survey on the dollar cost of each landing it didn’t surprise me that using auto-braking substantially increases brake and tyre servicing costs rather decreasing them. I don't know if that is a valid statement in this present era of flying. That said, auto brakes do at least ensure equal wear and tear on tyres, whereas manual braking relies on pilot technique. Heavy footed pilots do not always brake evenly on both pedals.

In a similar vein, it is well known that in terms of overall cost saving, use of reduced thrust for take off can give significant savings in maintenance. Yet it seems many operators disregard the potential cost savings available on tyre wear and tear with manual brake landings. For pilots, their manual braking skills inevitably decline due lack of use. Does that matter nowadays? Probably not.

Why would use of autobrake be associated with heavy braking? Doesn't the pilot have a choice of braking level for all autobrake systems?

The cost of using autobrake unnecessarily is, obviously, higher than not using any brakes or very little manual braking.

The cost of using autobrake to achieve the same thing as manual braking is lower.

My understanding is the autobrakes will apply at touchdown to get the target decel rate. Manual brakes are often applied after some energy has been expended by thrust reversers.

If you let the TRs do the decel down to, say 100kts, you will have saved a fair amount of energy from going into the brakes.

I thought that braking technique for carbon brakes in newer aircraft were different than the old 737-200. A good, smooth brake application was desired to warm them up nicely and reduce wear(Just avoid really high brake temps).

The cost of not braking sufficiently hard is much more if the outcome is an overrun.
The MD, and other manufactures advise was discussed by the ALAR group to consider any negative effect - mindset, of not braking hard in everyday use.
Unfortunately the 'we know better', the 'pilot can always intervene' views predominated; and overruns are still high on the accident list.

30+ years ago - while working on the development of the original 777 (and shortly after the fatal Lauda 767 in-flight T/R deployment) - I made the half serious suggestion that perhaps we should simply get rid of the reversers, maybe add a 'drag chute' that the pilots could deploy if they got nervous. Save weight and the costs/maintenance of the reversers.
The response was that proper use of the reversers reduced brake wear (and the associated maintenance) by over $100 per landing (figure the number would be more like $200-$300 in today's money).

Carbon brakes wear very differently to the steel brakes you're familiar with. Carbon brake wear is linked to number of applications which is why auto brake is preferred as it gives a single continuous application.

Reverse thrust can save your bacon on wet / contaminated runways or with compromised braking systems

It should never be deleted

Reducing the number of applications is a well established fact for carbon brakes. In addition to that, temperature matters.I recently read an Airbus article about carbon brake wear optimization with graphs for three different manufacturers (Messier-Bugatti, Goodrich, Honeywell), brake wear as a function of temperature, and they all look different. This is a cut out from the article, not necessairly very useful for the average line pilot (who hasn't got a clue which brake manufacturer is installed...) but shows there is no one size fits all approach.

4.2 To Optimize Brake Temperature

As demonstrated in Figure 1, the typical spectrum of carbon wear, versus carbon-disc temperature, illustrates how low-wear and high-wear vary with the disc temperatures. Therefore, operational recommendations to increase carbon brake life should aim to keep the carbon temperature outside the high-wear range. In order to increase carbon-brake life, the brakes should be operated in general when either cold or hot, but not at intermediate, warm temperatures. Pilots should receive simple instructions on brake operation, based on the average optimum temperature ranges for low carbon wear and in accordance with operational constraints. For example, based on data provided in Figure 1:
- For Messier-Bugatti brakes the pilot should receive instructions to taxi with an indicated brake temperature below 80 °C, or above 250 °C.
- For Honeywell-ALS brakes, the indicated temperature should be below 150 °C, or above 315 °C.
- For UTAS brakes, the indicated temperature should be significantly below 80 °C, or above 250 °C. These instructions must correspond to the specific brake type of the aircraft, and to the specific operating conditions. This is because, as demonstrated in Figure 1, the relationship between carbon wear and approximate brake temperature varies significantly between different brake types.

I was cluelss about carbon brakes until I found this video about 14 years ago. Best explanation you will find on the internet.

Yes. As well, most of the brake wear occurs on taxi out, not on landing.

A pet peeve of mine is people who disconnect the autobrake by a stab on the brakes, then proceed to jerk their way down the runway then brake harder and harder to make a turnoff that would have worked nicely if the AB had been left in. As a passenger it’s not a great experience and hard braking late on makes you wonder if an overrun is imminent. Same with parking - smoothly onto the stand then full on the brakes at the very end when you have a readout of your groundspeed and also the exact distance to run. Aaarggh!

Does the number varies depending on the price of fuel?

Nice to see MD-80 flight test aircraft fuselage 909 at 8:04 in the video.

It’s all interesting information, but threads like these remind me that there are people making a living trying to figure out exactly how, what, when and where we use brakes/packs/APU’s/single engine OPS/ECON climb/CI 0-100/Type IV/etc. And wether it’s even worth changing an SOP based on that info.

We pilots often think we can second guess their efforts, but it’s almost futile.

Back around 1980 at Gatwick, Laker AW BAC 1-11s used reverse idle and braked to make a turn off to save engine wear, whereas BCAL used full reverse to save on brake wear.

They were likely both exactly right for their circumstances.

A possible scenario is that AW owned the engines. Treating it with kid gloves was worth it at overhaul time at the expense of brakes.
BCAL may have had a power by the hour arrangement. The extent of the overhaul wasn’t their problem. But brakes were.

As alluded to above, there are a lot of financial variables that go into this that a mere pilot will not have the data to be expert in. The bean counters do.

Do what the company says, unless you think there’s a safer way that day. That’s what your fourth stripe is for.

A lot of big airlines have set costs whatever the number of brake units replaced. The only difference in cost is that of man hours to change the units. The SOP at my airline on the A321 is to aim for Flap 3 landings, idle reverse, with auto brake on LO until taxi speed. This is of course unless performance dictates otherwise. Someone clever who knows more about overheads than me has done the maths, and I'm fine with that. As alluded to by someone earlier, I just wish more pilots would leave the auto brake in until it needs to be disconnected. This helps even out the brake temperatures for the turnaround, and also evens the brake/tyre wear.

As a point of information for the OP, I’m guessing your experience was with medium auto brakes. MED is seldom used in the real world, because the declaration is excessive. On all but the newest A320’s, low is too little deceleration. In the sim, low tends to have you sliding about a bunch, so that’s probably why he used medium.

I was jumpseating the other day on a B737-800 NG and we landed at Flap30 auto brake 3. Like some of the comments above the auto brakes were kicked out relatively early and manual braking was definitely uneven and sporadic as you could feel the aircraft pulling to each side. The interesting part I found was it was a very quick taxi(3 minutes) to the bay and by the time we got there the left brake was shuddering which was shaking the whole aircraft with every application.
I’m interested to know and hopefully people here with more experience on the 737 can help with, how many brake applications have they found contributes to the shuddering as there couldn’t have been that much heat in them or was it the cold wear of the brakes with the little carbon particles breaking off causing the shuddering.

Not sure exactly, but I have noticed some brakes are definitely worse than others - perhaps uneven wear on the left vs right causing different amounts of heat build up.

The 737-800 has the worst brakes out of any Boeing I've flown - can be quite difficult to apply evenly and without dancing down the runway, especially with moderate application.

I tend to leave the auto brakes in as long as possible for this reason - much smoother application. My pet peeve is the heavy braking to make a rapid exit instead of taking an extra minute to taxi back to the bay.

On the 717 we use, there are no autobrakes. Typically wait until 100 knots or below before applying brakes if it is safe enough.
Often 30mminutes turns so brake heating may be an issue. The brake fans from MX work well if needed.

On the Airbus, a few things I have learnt from their official documentations:
* Do not ride the brakes. In a straight line let the aircraft accelerate up to 30 kts then one smooth application down to 10kt.
* Minimise the brakes applications as much as possible.
* Know the critical brakes wear temperature. It varies from manufacturer. On The Messier the worst temperature is around 180 degrees celcius.
* After landing consider the last high-speed taxiway to vacate (if no restrictions) to minimise the use of brakes.
* Consider single engine taxi also to minimise the braking.
* Wait at least 5 min after landing to set the brakes fans or entering the gate whichever comes first unless you expect the brakes to exceed 500 degrees.

Probably being done as a helpful technique to educate those passengers who like to jump up while the aircraft’s still moving…
(and no, I’m not seriously advocating this and have never personally done it)

I know some do that. I try not to as the cabin crew in our operation is already up and not in their seats because they are already disarming the doors.

Sometimes it happens anyway, had it the other day when pulling into a parking stand in ZRH when the parking system jumped from 0.8m to STOP.

It is quite possible to bring the aircraft, at least big Boeing aircraft, to a stop at the gate without any feeling to the pax that the aircraft stopped. It is just a matter of watching the GS and outside reference and smoothly increasing brake pressure appropriately as the stopping point is approached.

I can honestly say that I have never once looked at the GS on big aircraft when parking them! No complaints in 35 years.

You'd want to be reducing brake pressure as you approach the stop point or you just increase the rate of deceleration.

But I'm sure you know that.

Bigger aircraft were always much easier to be smooth - the smaller jets (737) were always harder. That's true for the entire operation - larger jets I found easier to fly / handle / park.

MED is used all the time in winter up here. Low is all but useless once it gets a little slippery.

if low is useless in slippery conditions then selecting MED will have very little effect on the landing distance.

LOW and MED give a preset rate of deceleration. If low is unable to achieve the target rate of deceleration due to a slippery runway selecting MED or even max manual braking won’t increase the rate of deceleration. Increased braking effort will only make a difference if you pass over patches of grip and if that’s only on one side you run the risk of a rapid yaw and then potentially going off the side.

Spoilers and reverse thrust are your friends on slippery runways as they’re symmetrical.

LD

Locked door
It’s not the lack of friction that’s limiting. It’s the time it takes to kick in.

There was a SB a few years ago so in LO now takes 2 second to kick in not 4 as manufactured, which many found a little tardy. Not all aircraft have it.