Operationally unnecessary use of B737 Autobrakes

[Tee Emm]

The B737 FCTM states: "Boeing recommend that whenever runway limited, using higher than normal approach speeds, landing on slippery runways or landing in a crosswind, the autobrake system be used.

In short, you do not need to use the autobrakes unless any of the above conditions apply. Mind you, there may be a good case for using the autobrakes if an early turn off is planned at certain runways. In other words a virtual performance limit landing.

Since the majority of landings are safely outside those described in the above FCTM extract, it could be argued there is no operational need for autobrake use as SOP for all landings; not forgetting the additional tyre wear and brake heating that must occur with instant braking at spin up.

Manual braking requires a certain amount of panache and skill; whether used early or later in the landing run. Autobraking requires no special skills. One only has to observe in simulator training the swerving along a runway as autobrake aficionados try their unpracticed hand (or should I say, feet) at manual braking. :rolleyes:
On reflection, perhaps that is why some pilots love autobrakes:ok:

An observer could easily gain the impression that autobrake use is overdone - to the extent that pilots turn it into a standard operating procedure (company directed or pilot choice) -even though there is no obvious operational requirement.
Maybe this shows up as just another example of lazy flying techniques along with automation dependancy (see numerous current posts on that subject

[ampclamp]

Most skippers I've dealt with are happy enough to accept an aircraft with auto brake inop depending on destination runway and conditions of course.
I am not across our mobs directions in A/B use in day to day ops.

However in the old days when I could dispatch a 737 without any A/P I've had f/o's in particular happy as larry to actually fly it and one skipper nearly crapped himself at the prospect.

In the Boeing notes you quote , are they not saying you should use A/B under those conditions and not risk manual braking, not the inference that you should not use A/B under "normal" conditions as you suggest?

[lederhosen]

An interesting topic and I fully agree that if you always use autobrake and never brake yourself you may be a bit rusty when you have to for some reason. I think it is like other problems arising from overuse of automation, you need to be familiar with all modes of operation and vary your game.

There are plenty of arguments in the other direction. Indeed I think part of the overrun problem in Chicago with Southwest was that the pilots were not familiar with the autobrake system. The brake to vacate concept is also on its way at least with airbus. I have certainly heard that the automatics are softer on brakewear when used properly.

As an aside as a sim instructor I find people tend to be a lot less smooth manouevering on the ground in the sim than in the aircraft, perhaps due to sim fidelity problems and lack of cues that are available in the real aircraft.

[Tee Emm]

In the Boeing notes you quote , are they not saying you should use A/B under those conditions and not risk manual braking, not the inference that you should not use A/B under "normal" conditions as you suggest?

I agree it is a matter of interpretation. I think what Boeing mean is that there may be no pressing need to use autobrakes on normal operations except under the conditions the FCTM specifies where use of autobrakes is recommended.

[lederhosen]

It is clear that is what you assume. My interpretation is that Boeing leaves it open. My company encourages autobrake usage. Over the last few years we have gone from your approach or something similar to the view that the autobrake is a useful tool in normal operations. Ten years ago for example the view was that autobrake one was for the limp wristed. Now we encourage its use where appropriate.

If you were involved in a runway excursion do you think the investigator would ask if you had selected autobrake? Some things are black and white, stabilised approach criteria for example. But autobrake usage is left open and I suggest people follow their own company guidelines.

[Agaricus bisporus]

I think use of autobrake does require skill.
Skill to use a suitable setting. It is almost always set one level too high in my experience.
Skill in releasing it - a fierce jab on the toe brakes that has everyone jerked into their straps is not very professional, yet almost always occurs.
Skill in releasing it at a sensible time. So often it is released (with that great stab on the pedals) almost as soon as it has started working - followed by jerky and uneven braking after that. If you don't want to use it then don't select it in the first place. If you do, leave it in to do its job, part of which has to so with passenger comfort.

Manual braking is seldom done smoothly, so learn to do it properly or use the bloody automatics! Please!

[safetypee]

I don’t see any logic in the Boeing advice in an idealised operation; what safety advantage does autobrake have over manual braking?
Researching this I find that Boeing’s recommendation to use autobrake on ‘slippery’ runways “assures prompt application of brakes after touchdown”, but then cautions that “autobrake performance capability is limited by runway friction” and that the published performance is based on the assumed runway friction (‘Stopping on Slippery Runways’ July 2001 et al).
This implies that the advice is to accommodate less than optimum pilot performance, yet recognises weakness in assessing the runway condition and selecting an appropriate autobrake setting.

However, a later version of the Boeing presentation Landing on Slippery Runways (www.smartcockpit.com/flightops) provides a balanced view – use autobrake or manual (slide 35), use auto brake on wet / slippery runways (slide 36), but for manual braking on short slippery runway use full brake pedal pressure (slide 37). This also points out the hazards of incorrect (too low) autobrake level for the conditions and that autobrake used with reverse may not be as good as manual braking with reverse in low friction braking conditons.

As I recall, the need for autobrake was driven by poor manual braking performance during RTO’s. Subsequently the system has been ‘sold’ to operators as having economic advantage and for passenger comfort, neither of which should dominate operations, particularly in the conditions cited by Boeing.

IMHO, autobrake has contributed to many incidents and perhaps some accidents due to habitual use without appropriate thought or background knowledge; hallmarks of automatic dependency.

[John Boeman]

Couldn't agree more with every word you have written there Agaricus bisporous.

Autobrake also almost always causes less heat generation in the brakes so presumably less wear.

[safetypee]

JB have you considered that when using autobrake and reverse together, the autobrake demand is backed off, thus the brakes may not be used, i.e the deceleration comes from reverse, thus you would expect less brake heat.
Without reverse, comparing autobrake with manual brake, then with equal brake application in both cases, the brake wear / temp should be the same, i.e there is no advantage from autobrake. See pages 10-15 in the link above – landing on slippery runways.
In practice, there may be an economic advantage for autobrake due to the rate and evenness of brake application, but the economics should not be a consideration on a limiting or slippery runway.

JB and Ab – ‘skill in setting the level of autobrake’; in most accidents involving autobrake the setting was too low.
A professional pilot must develop, and continue to improve the skills of aircraft handling. There is no excuse for not using manual braking. In addition, manual braking provides opportunity for skills of judgement by developing experiences of brake pedal angle/force with the reported runway condition, similarly for stopping distance.

[STBYRUD]

I wouldnt make this an issue of 'training' for the event that autobrake doesnt do its job. In my opinion thats like saying that "I dont want anti lock brakes and traction control on my car because I will otherwise not know how to accelerate gently and how to use cadence braking if the road is slippery. Every aircraft tends to feel slightly different, each runway surface is different, each set of tyres is different. Autobrake (up to a certain level) aims for a set deceleration rate, when it cant reach it with the maximum brake pressure for the setting youre probably not using enough reverser or the runway is slippery. Yeah, on a three kilometer runway you'll probably fine with 'autobrake off' - even without any wheel braking at all and idle reverse if youre okay with vacating at the end, but why would you? From what I have witnessed people tend to increase brake pressure as they slow down because that intersection they were planning for suddenly comes closer and closer, not comfortable for the pax, can't be great for the brakes either. Autobrake gives you a ballpark figure for rollout distance that you can ensure with reverse thrust if necessary.
BUT - from what I understand, if youre using carbon brakes, proper manual braking techniques (push the brakes and keep'em there) can increase service life and reduce heating greatly since autobrake might rapidly modulate... Not a black and white issue as usual.

[Prober]

As I understand it, the optimum benefit of autobrake is achieved in the first few seconds of use i.e. immediately after touchdown. My experience (757, not 737) is that the best performance, on a normal dry runway, is achieved by a gently increasing pressure on the brake pedals thus disconnecting the auto system by about 100 kts. One gets a smooth and undiscernable transition to manual braking and one immediately gets a feel for the aircraft behavior. I teach avoidance of hard braking later in the landing run, disconnecting by a forward movement of the speedbrake lever or by switching off the autobrake switch (and also NOT by a forward movement of the thrust levers!!). Any of these will cause an abrupt change of brake pressure and consequent passenger discomfort. Reverting to the original question, I have always found Boeings to be extraordinarily obscure, obtuse or even obfuscating in their wording of their manuals. I would read the quote as to mean that it is certainly NOT necessary to use autobrake in circumstances other than those mentioned. They would leave it to the pilot’s discretion. What one’s company thinks is, of course, another matter.
Prober

[John Boeman]

Safetypee, I had a feeling that keeping my post so short would come back to bite me. BTW I too am referring to 75/76 autobrakes.

Yes, I have been considering all the variables you mentioned during the many years I have been flying aircraft with autobrakes.

With regard to the comments made by AB and agreed with by me, what I was thinking about were the airports that we constantly use and are totally familiar with, when you have to sit and watch even the correct setting being overridden so that manual braking can be “practiced”.
I believe we were both talking about familiar airports in favorable conditions.

We also fly to airports with longer runways (Pisa for example) where I encourage the FO to leave the autobrakes off and just brake manually to get the feel of them there.
On longer runways where we want “to make” an earlier turn off I sometimes suggest using a lower setting initially and then increasing the auto setting if necessary when we have lost some speed in order to reduce the heat build up.

Equally if the runway is not particularly long or as familiar and the conditions or aircraft weight are less favorable I prefer to err on the high brake setting side!

When landing a 767 at Sanford, I know that early cancellation of autobrake followed by manual braking, always results in much higher brake temp readings than when letting the autobrakes continue the braking down to taxi speed.

At the company I work for, our sop is to use idle reverse only, where possible, so there are very few times when the reverse negates the brakes entirely and another thing that happens too often is idle reverse being cancelled at 60 kts instead of leaving it in until down to taxying speed. It is surprising how much braking is available from idle reverse even when below that speed.

Your statement “but the economics should not be a consideration on a limiting or slippery runway” really is rather stating the obvious. Also when you say “in most accidents involving autobrake the setting was too low,” I would wager that the the brake setting was a secondary factor in the accident and not the main cause.

“A professional pilot must develop, and continue to improve the skills of aircraft handling.” – no argument there.

“There is no excuse for not using manual braking.” What do you mean by that? That statement taken in isolation sounds strange. If you added something like “when the conditions are suitable and an individual needs the practice” then fair enough. Maybe we ought to take the autopilot out as well in order to make sure we all get enough handling practice.

As we all know, there are a multitude of variables, and dozens of ways to skin a cat.

[lederhosen]

Good post JB, I completely agree particularly about not cancelling the reversers too early. At the risk of digressing I have seen some comic braking despite the runway length from aircraft landing off the circle to land at Pisa whilst I was stood at the holding point.