Idle thrust reverser landings.

[West Coast]

Hopefully there's some of you in the know...

At airlines with idle thrust reverser landing policies, do you see a higher than expected increase in brake wear after its implementation?

I recognize few will have these answers, but a lot of diverse aviation backgrounds are present here, perhaps even some bean counters.

[Chesty Morgan]

Yes.
......

[anartificialhorizon]

Of course....

I understand the cost of brake wear/ ovehaul, as a result of increased braking is considered less than the increase in fuel and engine wear due to increased engine thrust used during reverse thrust.....

Economics....

[lomapaseo]

At airlines with idle thrust reverser landing policies, do you see a higher than expected increase in brake wear after its implementation?

No

the brake wear will be just about what one should expect when you use them harder

[Chesty Morgan]

RTFQ ;)

.......

[Goldenrivett]

Hi West Coast,

NASA conducted a survey in mid 90s; http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19950014289.pdf

Brake wear was about 25% higher with REV Idle v Full Reverse, but brakes are cheaper to service than the cost of extra fuel burned + reverse maintenance.

[tdracer]

Back during the initial development of the 777 (and shortly after the Lauda 767 crash when a reverser deployed in-flight) I semi-seriously asked the question of why didn't we just get rid of thrust reversers (at least at that time, we didn't even get any credit for them under FAA regulations).
One of the discussion points was that using reversers saved over $100/landing in brake wear and maintenance.

Sounds like a classic case of 'pay me now, or pay me later' :rolleyes:

[West Coast]

Thanks to the few who took the time to read the question prior to hitting the reply button. I fully expect an increase, what I asked is if it was above what was expected. Laws of unintended consequences is what I'm trying determine from other companies experiences.

Golden and TD, thanks, certainly something to consider.

[DaveReidUK]

No

the brake wear will be just about what one should expect when you use them harder

Pedantic, but spot-on. :ok:

RTFA. :O

[tubby linton]

The unintended consequence is that it becomes normal to the crew and passmgers only to use idle reverse ,and the selection of max and the associated noise suddenly becomes quite unusual. In the A321 max reverse seems to be full of sound and fury signifying nothing in the braking produced, but that is probably because the autobrakes are looking at the total decelleration being produced not that of a single retardation device.

[FlightDetent]

lompaseo: the only one to read the question :D.

WS I wonder how someone actually does measure brake wear and compare it before / after such policy is implemented (*). At the same time, many a task force / project group would certainly agree there is a brake wear increase, but the distinction between causality and confirmation bias is very hard to make. For sure, one who expects an increase is more likely to find one. :}

The manufacturer of the airframe I am current on declares that carbon brake wear is dependent on the number of applications and not on braking intensity, adding further that 75% of wear is attributable to taxi out with cooled brakes. So how much of those 25% does happen on the runway and will be affected by the policy? Next, the lowest wear per application is supposed to be at about 220 deg C indicated temp, consequently more strain during the rollout would give you less wear on taxi in. Hmm. Then there is the maybe-not-so-apocryphal story (heard of it on PPRuNe, must be true then) of a BA reverser / autobrake wear assesment which showed more wear with autobrake plus reversers ... on one particular type but with different results on another fleet!? While on the subject of autobrake: idle reverser policy will likely bring manatory autobrake, hence on long runways with far exit, where sensible pilots now may use no autobrake + idle, with ABRK + idle you will get a wear increase plus extended taxi time so $$ out of both windows... We could go on for pages like this. :(

Best of luck with the assigment, honestly. But I would not bet my personal money on the result irrespective of which one it was (even the one I agreed with) :E To rub more salt, chances are the decision whether to proceed or not will neither be a technical one, nor of direct operating costs at all.


regards, FD
* implemented = announced? published ? trained ? executed by line pilots?

[wanabee777]

Some airport authorities (eg Narita ) request idle reverse only unless more is needed. I forget the exact wording.

This was for noise consideration of the surrounding communities near the airport.

I generally, never used anything but idle reverse unless the runway was wet or contaminated.

In the MD-88 you could cause directional control problems by selecting full reverse because it would diminish the effectiveness of the rudder.

One stormy night at LGA I used maximum reverse on a 727 which resulted in the center engine popping off a few compressor stalls. The tower controller started yelling that we were on fire because of the display.

[tubby linton]

My airline measures the acidity of the hydraulic fluid. The fluid changes Ph due to it being heated by braking . We operated a widebody Airbus for over twenty years predominately using full reverse and manual braking. In the latter years this was changed to idle reverse and manual braking to save fuel. It soon became very noticeable that the brake packs were being replaced more frequently and also the acidity of the hydraulic fluid was becoming noticably more acidic which then led to more hydraulic leaks as the seals were degrading.

[West Coast]

I wonder how someone actually does measure brake wear and compare it before / after such policy is implemented (*).

Exactly my conundrum.

[Goldenrivett]

Exactly my conundrum.

There is an Airbus Power Point on the subject Conf3.ppt (http://www.blackholes.org.uk/PP/conf3.ppt)

and I also found this: See Page 20 of this airlines Fleet Newsletter.
http://contentz.mkt932.com/lp/19805/101258/a320%20fleet%20newsletter%20to%20be%20merfed%20with%20fleet% 20article%20go%20around%20dec%202014.pdf

[mustangsally]

When landing on a 11000 foot runway(3,367 m) and the parking spot is off the left end of the runway, idle reverse on touch down and no auto brakes, had to add just a touch of power when turning off at the end. The aircraft was a 747-200 with a landing weight of about 350k lbs.(220k kilos), first touch on the brakes was at the parking spot. We always advised approach and tower that we would be rolling to the end. A couple of times we were asked to expedite the exit.


Reverse thrust produces better results at the higher speed. Below about 80 knots it is doing nil to help slow the craft.


Companies that demand use of reverse thrust and or us of auto brakes do so because of the lowest common denominator, the weakest captain.

[RAT 5]

What is the cost comparison of brake maintenance when using only idle REV, as is often demanded by many airports, and the cost of brakes using NO REV? This would then bring in the question of what is the cost of installing TR's in the first place. As they are not considered in normal RTOW calculations, nor landing, one wonders are they worth it? There has been smaller jets, Bae146, that didn't have any. People will know of more.

[Cough]

RAT5.

Its all very well taking them off....Until the runway becomes contaminated. Then you reap the benefit of fitting them...

[Rocket3837]

Brake wear of carbon brakes depends on how many times you use pedals and not on how hard you use them.
So I expect that there will be no extra cost if you use idle reverse.

[Intruder]

We got a note from our fleet manager that we're 'tearing up' 748 brakes using the procedures designed for 744s (Flaps 25, idle reverse). Pix included showed brake assemblies with 'major damage'. no indication of similar damage on the 744s.

It should be obvious that when landing a heavier airplane at near its limit weight, using procedures for lighter airplanes may not necessarily work well. While the 748 brakes and tires are bigger/heavier, they are apparently pushing the limits as well.

FWIW, I've adopted the following personal guidelines, to reduce max tire speeds and brake energy:
For takeoff, Flaps 20 at 320 Tonnes or above. That goes along with the concept that the 744 is 'heavy' because bank is restricted with flaps up below Flaps UP+20 speed [FCTM 3.37: "747-400 Above 680,000 lbs (309,000 kgs), limit bank angle to 15° with flaps up until reaching UP + 20 knots."]

For landing, Flaps 30 at 250 Tonnes or above. Max reverse if Autobrakes 3 or above required for landing performance. 250T is the baseline landing weight for performance charts, so I assume anything above that is "heavy".

YMMV, and you may have different views on performance...

[KBPsen]

The most incredible thing is that no one have asked what type the question is aimed at.

[Centaurus]

Brake wear was about 25% higher with REV Idle v Full Reverse, but brakes are cheaper to service than the cost of extra fuel burned + reverse maintenance.



From the Boeing 737 FCTM:

"The importance of establishing the desired reverse thrust level as soon as possible after touchdown cannot be overemphasized. This minimizes brake temperatures and tire and brake wear and reduces stopping distance on very slippery runways.

The use of minimum reverse thrust as compared to maximum reverse thrust can double the brake energy requirements and result in brake temperatures much higher than normal."
............................................................ ............................................................ ......................................................

The problem with only using idle reverse after touchdown is that some aircraft such as the 737 will drop to ground idle of 23%N1 if after 4 seconds reverse has not been selected. If for some operational reason during the landing run, the pilot suddenly decides full reverse is needed, it can take up to 10 seconds before full reverse spools up from idle reverse. As the aircraft slows on the landing run, reverse becomes less effective as a braking medium, and the situation is made worse by the long spool up time from reverse idle.

The other factor to remember, especially on 30 minute turn around times that some LLC use, is that the brake temperatures can be much higher than normal if landing using idle reverse (see Boeing TCTM advice above).

That means the next take off after the 30 minute turn around will start with already hot brakes. Not good airmanship. In turn the already hot brakes could reduce the braking efficiency if a high speed rejected take off should subsequently occur. Plus possibility of brake fire after stopping due max brake energy exceeded.

[RAT 5]

Cough: quite right, I agree. I was curious, as the comparison is all about costings, just what the overall cost analysis was of all the various combinations. Of course, the takeoff & landing performance on slippery runways would be compromised. So let's keep them on.
Idle REV and minimum turnarounds, as operated by some we love & hate, has always been a question. I wonder if those guys do brake cooling calculations Before & After every landing, or would it be too complicated, confusing, embarrassing etc.

[wanabee777]

When landing on a dry runway at normal landing gross weights, I rarely selected more than idle reverse thrust if my planned runway turnoff point was greater than 6000 ft from touchdown.

But hey, that's just me.:)

Some guys go to maximum reverse no matter how much runway they have remaining.

[Chesty Morgan]

Idle REV and minimum turnarounds, as operated by some we love & hate, has always been a question. I wonder if those guys do brake cooling calculations Before & After every landing, or would it be too complicated, confusing, embarrassing etc.

Don't need to. There's a Quick Turnaround weight limit provided in the QRH.

Notwithstanding that, I tend to do landing perf. and brake cooling calculations anyway and I don't really get minimum turnaround times.

[Monarch Man]

Try landing a 777-300 or 300ER at MLW or close too and ISA+25 with a 75min turn using idle only.
Hmmmm I can smell hot brakes :sad:

[wanabee777]

You forgot the 10kt tailwind.:O