B737-300\400\500 questions N2

[B737africa]

I have notice that in one airline using the B737 300/400/500 ,all the pilots do not use the AUTOBRAKES on landing because it is too hard on the brakes ,instead they are using manual braking for saving the brakes and tires.
I do not personal agree with it , but maybe someone can give me a confirm of it?
Thanks

[STBYRUD]

To me that doesn't make any sense at all, I hardly doubt that autobrake usage is 'harder on the brakes' than manual braking, especially since it scales with reverse thrust usage...

[ant1]

I guess you refer to the practice of letting her roll before applying brakes when the runway is (much?) longer than required. It is gentler on the brakes but I will leave others with more experience comment on the good airmanship of that practice which I have witnessed.

Fly safe, land right

[Lufthansa_NFF]

I my company it is "recommended" to use autobrake ( CAT III -> "must"), but most of us dont use them, except the runway is short/wet/cont.

my opinion: let the a/c brake with the friction of the rwy + idle reverse + speedbrake until passing approx. 100 knots and then smoothly apply brakes -> cooler brakes and less brake wear!

just my 2 cents!

[Nightrider]

Brake-wear is varies with the number of applications. A one time application, as with autobrake, shows the least wear.
To keep an aircraft rolling with just reversers in idle and no braking is not a very safe procedure, slowing down in a timely manner, i.e. autobrake 1, to below 60 kn will enhance safety in case of any unforeseen problem.

[Lufthansa_NFF]

@ nightrider

i dont think so!

use of brakes from 130 knots to 60 has more wear of the brakes than from 100 knots to 60 and produces more heat! furthermore it is as safe as with autobrake, IF you have a sufficient long runway (>3000m) and no need to leave the rwy early!
it wasnt the question, if you use autobrake on a short wet runway in winter!

in your opinion: what is unsafe in just letting the ac go itself for a few meters before applying brakes?

e.g. in EDDF with a runway of 4000m my technique works out pretty good! :ok:

[ant1]

Boeing discourages the use of A/B 1. It's a deceleration rate very close to that obtained with reversers only which causes the A/B system to modulate instead of applying steady breaking which as you said causes the least wear.

[B737africa]

It seem to me tha we , Professional pilots, are getting like the doctors in the hospital, where intead to worry how to cure the patients they worry how much medicines they are given away and their cost.
Now taking example from them , why do we have to care if the mechanics change the tires or the brakes more often due to their usage?We have all those system on board in order to be used and not just to look at .
Long time ago I was flying in USA for a company that was using the Casa 212 .
in our training our chief pilot rather worry about the safety of the flight , he was worry of what the mechanics have to say if we were using to much oxygen on board, as for company training policy the usage of the oxygen was limited only to 15 minutes before the landing and not continuous but to be split with the other pilot on board , yes split, and in order to impose this policy the company removed one oxygen mask from the airplane (cargo airplane) to avoid that both pilots were using at the same time the oxygen.

[BOAC]

All crews should be encouraged to use A/B commensurate with landing roll required/runway condition (using the Boeing tables) from A/B Max/full reverse down to no A/B (and no reverse) as necessary. Any 'fixed' setting of A/B or reverse is crazy and can cause intense annoyance to ATC and other runway users.

Certainly the use of A/B 1 is reckoned to increase brake wear.

[B737africa]

Thank you BOAC (http://www.pprune.org/members/14135-boac).
Now that is the answer I was looking forward to know.
The use of the A/B according Boeing procedure .

[Centaurus]

Around 1975, Boeing held flight operations symposiums for 737 and 727 operators. One of the subjects was autobrake use. At the time the FCTM stated that use of autobrakes would reduce wear and tear on the tyres. The operators complained that, on the contrary, their experience was wear on brakes and tyres had increased significantly since auto brakes were used.

Boeing was forced to amplify its FCTM comments by explaining that manual braking wear and tear depending largely on technique used by the pilot. As some pilots were known to be heavy brakers and others more considerate of braking requirements,the wear and tear throughout a fleet of Boeings would vary considerably.

By using autobrakes, Boeing admitted that brake and tyre wear increased but this would be evenly spread among the fleet thus helping with maintenance scheduling.

Boeing then withdrew the FCTM advice on wear and tear, replacing the offending paragraph with the current wording - which is now:

"Boeing recommends that whenever runway limited, using higher than normal approach speeds, landing on slippery runways or landing in a crosswind, the autobrake system should be used. For the normal operation of the autobrake system select a deceleration setting". A table of settings was given to cover the description given above.

Boeing added that where landing conditions were suitable - meaning not runway limited or as above - there was no need for autobrake use.

The company I flew with dispensed with autobrake use except for the conditions described by Boeing. For the 737 the vast majority of runways in in Australia and the Pacific island states were anywhere between 5500 ft and 8000 ft in length, and did not require the use of autobrake. That said, noise abatement was rarely a restriction.

[Tee Emm]

Boeing discourages the use of A/B 1.

Unable to locate that advice in the 737 FCOM or FCTM. What Boeing publication are you referring to?

[BOAC]

Tee - it could be in the realms of folk-lore - it was certainly 'preached' a decade or more ago on the basis that A/B1 causes a relatively light 'drag' on the brakes which is more 'wearing' than a considered and measured positive manual braking effort. I have no reference for it other than vestigial memory of Ops Manuals 'of old' as I assume ant 1 and Centaurus have. Things often 'disappear' from FCOMs and the like for many reasons including liability issues.

There is nothing wrong with using A/B1 to assure early braking application but I recall it was thought to be the retention of A/B1 down to lowish speeds with the A/B modulating with reverse thrust that caused the increased (and unnecessary) wear and regrettably many companies made A/B1 the 'automatic and thoughtless' minimum 'norm' for all landings when often it was not needed.

[IRRenewal]

From the NG FCTM:


Carbon Brake Life

For carbon brakes (as installed), brake wear is primarily dependent upon the number of brake applications. For example, one firm brake application causes less wear than several light applications. Continuous light applications of the brakes to keep the airplane from accelerating over a long period of time (riding the brakes) to maintain a constant taxi speed produces more wear than proper brake application.

During taxi, proper braking should involve applying brakes to decelerate the airplane, releasing the brakes when the lower speed is attained and allowing the airplane to accelerate, then repeating.

During landing, one hard, high energy, long-duration brake application produces the same amount of wear as a light, low-energy, short application. This is different from steel brakes that wear as a function of the energy input during the stop.

For normal landing conditions, autobrakes 2 or 3 optimizes brake wear, passenger comfort, and stopping performance. Since autobrake settings apply the brakes dependant upon the deceleration rate, an autobrake setting of 1 results in a higher probability that the autobrakes will modulate, especially when the reversers are used. Autobrakes 2 or 3 results in a continuous brake application, which can increase carbon brake life.

It all depends on what type of brakes you have. According to the quote above A/B1 seems a less than optimum choice IF you have carbon brakes. Having said that, I personally can't remember ever using A/B1 on landing.

[Centaurus]

For normal landing conditions, autobrakes 2 or 3 optimizes brake wear, passenger comfort, and stopping performance.

I don't know about the NG but autobrake 3 in the Classics certainly doesn't enhance passenger comfort -far from it, as it is quite savage. Good performance - yes.

[uchy]

hello 1 question, also if it is not about ab.
I am not one professional pilot i have just one ppl. I saw in the 737 cl that the pilot put before takeoff one line to 80 one to v1 one to vr one to 210 and obe to v2+15. Why to v2+15?what does this speed mean?thanks a lot