Operationally unnecessary use of autobrakes for landing

[Skyjob]

The use of reverse is operator and operation dependent.

If one operator has comfortable long turnaround then reverse in excess of idle may not be required, however a loco with 25 minutes is unable to achieve the same without leaving brakes off during turn around to allow them to cool, which in itself raises safety issues (see recent loco rolling over apron pictures elsewhere as it wasn't chocked properly by ground staff).

To generalise the (non-)use of auto brake and reverse therefore is a typical no-go area unless comparing like for like operations.

I agree as per several prior posters, Boeing recommends that a MINIMUM of idle reverse should always be selected, it helps having the levers in the correct position in the unlikely case of having to use any when it becomes too late to spool up having not (yet) selected it.

To use reverse thrust and what brake setting depends on operation and operator schedule of flights to be performed.

Too many pilots take the recommended landing distances and treat it as gospel in some airlines, but fail to use the recommended brake cooling charts properly, even though BOTH are labelled ADVISORY in the Performance Inflight section of the QRH.

Furthermore many pilots are UNAWARE that brakes can only cool when released (extended or retracted, inflight and when ground [can only be set on ground]) or over a much longer prolonged time when brakes are set which is NOT documented by Boeing in PI and thus no guidelines exist for such configuration.

In a Boeing presentation over a decade ago the relationship was properly documented, but most pilots have yet to see the presentation as it is not readily available to crew. This presentation also described the different rates of cooling, risks with not using reverse and the history behind brake wearing pins, a must read to fully understand the subject.

So before this discussion goes a lot further about who is right and wrong, let's acknowledge the fact that different operators have different turnaround times and thus by definition have different requirements, regardless of aircraft type flown, so a comparison of who is right cannot be made unless restricting the conversation to that single type of operation.

A loco used to have a standard landing policy until an overrun occurred.
It changed procedures requiring crew to check landing distance and removed landing policy.
Resultant many crew used higher auto brake settings but failed to slow down first (similar to racing on the outside lane on the motorway then last moment hitting brakes hard to make the exit coming up), so brake cooling charts were laminated on reverse of landing distance charts.
All good, but if crew are not taught to release brakes and see a 20 minute requirement as sufficient because they have a 25 minute turnaround, the process fails. It fails in inadequate training of system knowledge and understanding of system limitations.

Recent command upgrade candidates at same airline report that (since their initial performance course at intake many years ago) the subsequent performance course during upgrade ground school has again made no reference to any brake cooling requirements whatsoever. This is not an isolated case.

[alf5071h]

FW, #18
“…check the landing performance” - an absolute must for all landings as this generates opportunity (a reminder) to think about safety margins. In wet / contaminated conditions the next worse runway condition should be considered as ‘a what if’ the existing report is in error.

I suspect that the new Boeing landing distance data will be based on Operational Landing Distances (OLD/FOLD) which has already been published by Airbus (outcome of TALPA meetings). The data should be more representative of the ‘actual’ operationally achievable distance; however the existing ‘test pilot’ based data – fully factored, is still relevant for dispatch, and is used in many European interpretations of the prelanding assessment as required by EU-OPS

http://www.pprune.org/tech-log/49803...ns-airbus.html

http://www.skybrary.aero/bookshelf/books/2066.pdf
N.B. EASA quotes the Boeing advice on autobrake use – perhaps without thought.

[No Fly Zone]

To Autobrake or Not to Autobrake, That is the...

The original post asks good questions. Many of the replies touch on this... but only a few waive the flag: Perhaps those committed AB2 pilots do not know HOW to do manual braking - Correctly. When truly needed, of course. When no braking or Rv-Th is necessary and you're going to the end anyway, why use either? One of the better debates in many months!

[Intruder]

I’m intrigued by the "hot weather" procedure.
For given landing the amount of energy to be dissipated is constant. This should total Brakes + Aerodynamic + Reverse. The contributions of autobrake or manual brake without reverse should be identical – irrespective of braking level; with reverse, autobrake might better optimise the contribution of reverse, thus would absorb less energy. This should give a cooler brake than manual brake if used at a similar stage of landing, but probably not greatly different if manual is used later as the effect of reverse diminishes.
Thus why would manual braking result in a cooler brake?

To add to what FullWings already responded...

Autobrakes by design come on at touchdown. Further, Boeing programs all except the MAX setting to give a constant deceleration rate (knots/second). Therefore, significantly more energy (e=mv**2) is absorbed by the brakes in the first 10 knots of deceleration than in the last 10 knots -- even given the use of reversers, as they have a relatively long spool-up time. If you allow half the ground speed to be dissipated without braking, you will have only 1/4 of the total energy remaining to be absorbed by the brakes.

So, if you delay braking by using manual brakes only, AND use a reasonable deceleration rate for the remaining distance using brakes, the brakes AND TIRES will absorb considerably less energy, resulting in much lower temperatures.

The listing as a "hot weather" procedure is likely a carryover from the days of the 747 Classic, which was VERY sensitive to brake abuse, especially at higher ambient temps.

[Denti]

As everything a lot depends on type apparently. On the minibus auto brake comes on after a time delay depending on the AB setting, which can be enough to achieve the commanded deceleration by other means. And at least on the mini boeing AB MAX commands a (actually two different) fixed deceleration rate, the higher one below 80kts.

In my outfit idle reverse is normal SOP, as is the use of auto rake although auto brake OFF is an allowed setting as well. However, brakes are cheap, engines are not, therefore there is a certain focus to not use more than idle reverse if possible, rather use a higher AB setting instead. Landing performance has to be checked, except on dry runways longer than 2000m for the mini boeing. EFBs make that easy enough anyway both for dispatch and inflight and take into account the chosen AB setting, as well as displaying the non factored and factored (dispatch full factor, inflight min 15% on the bus and min 20% on the Boeing) landing distance as well as the margin to the full runway length.

[galdian]

Strangely enough - by default - Mr Boeing says AUTOBRAKE is nice to have but if you don't have it....well that's OK as well.

Happy to be corrected but MEL allows dispatch with AUTOBRAKE system U/S and with NO performance limitations for runway condition, X/winds etc.

So scary!!

Sounds like some would be sitting on the edge of their seat for the landings, waiting for the "...oh the inhumanity!..." result that has now....maybe....all but been compelled.

[Intruder]

Indeed, there is often a HUGE difference between "best practice" and "minimum required".

IMO, reverse idle on EVERY landing is a "best practice". Autobrakes are nice to have, but certainly not "required" in most cases.

[tdracer]

Back in the early 1990s, I joined the 777 development program, shortly after I'd concluded my portion of the investigation into the Lauda 767 crash (t/r deployment in-flight).
After joining the 777, I brought up the idea of just getting rid of the thrust reversers - they are heavy, expensive, high maintenance, they'd directly caused at least two fatal accidents, and we didn't get any direct credit for having them (that last one has since changed, at least for EASA). I was told that, aside from their obvious value on low-friction runways, use of thrust reversers saved ~$100/landing in brake wear .
Getting those reversers deployed - if only at idle to kill any forward thrust - is important.

[Skyjob]

Getting those reversers deployed - if only at idle to kill any forward thrust - is important.

Wholeheartedly agreed!

[Mad (Flt) Scientist]

Originally Posted by alf5071h

Manufacturers’ recommendations being interpreted as ‘must’ (legal overtones).

And even worse, assuming that a recommendation of X in circumstances Y is not only a MUST but also a "MUST NOT" (or even "should not") in any other circumstances. Which is a pretty basic logic flaw.

When I am involved in writing a recommendation and leave some circumstances uncovered, that is (usually) deliberate - I am choosing to not take a position, to allow operational freedom. Reading more into it than that is unwise.

[JammedStab]

Thank goodness they Boeing kept TR's. They are critical on slippery runways. I believe the procedure for the BAe 146 is to start shutting down engines if runway remaining becomes critical when it is slippery.

Originally Posted by Intruder

Boeing does not recommend the sue of Autobrakes 1 on the 744, because it causes the wheel brakes to cycle, which is detrimental to carbon brake life. So, if Autobrakes are used at all, it's 2 or above.

From the 747 FCTM. The second paragraph was written in the revision highlights area of a recent FCTM update describing the reason for adding the first paragraph which was one of the revisions.

"For normal landing conditions, autobrakes 2 or 3 optimizes brake wear, passenger comfort, and stopping performance. Autobrakes 2 or 3 results in higher brake surface temperature and shorter stopping distances, which can increase carbon brake life."

"This change is a result of a cross-model analysis of carbon brake systems by Boeing engineering. The analysis revealed that brake modulation during autobrake 1 is unlikely, but possible."

[Yaw String]

The use of Reverse idle on Boeing aircraft,will activate Speed-brakes,if,for any reason you manage to land without having armed them.....This is SOP in my company.
Regarding use of Autobrake,most large airports require you to expedite exit from the active runway,leaving you with little freedom to choose! Noise constraints often dissuade the use of full reverse..

For the coolest brakes on landing on limited runways,at higher weights,full reverse at touchdown,followed by a good portion of manual braking below 100 knots,when the reversers lose their effectiveness works quite well....if performance allows...

On the later Boeings,initiating manual braking at too low a speed can give higher individual brake temps,due the taxi brake release system applying brakes to half of each braking pair......

[Gillegan]

One of the more interesting subjects that I've seen discussed here for awhile. The variety of responses indicates something that I've felt for awhile; that Brake Energy Management is one of the more misunderstood subjects in commercial aviation.

As a long time trainer on large airplanes (A300/B777/B787), and an aero engineer, I'm disturbed by the one-size fits all approach that some individuals and/or some airlines take. Given that both manufacturer's autobrake systems generally command a rate of deceleration, for a given autobrake setting: with idle reverse, you are more or less doubling your brake energy vs. using full reverse thrust. If you are going to manage your brakes effectively, you will need to consider the turn-around time for the aircraft. In some situations, idle reverse may be appropriate, and in some IT WILL NOT - especially for larger aircraft where runway margins are obviously less.

A little known fact is that brake certification requirements were drawn up before brake energy phenomena were really understood. The result is that on earlier certified aircraft, if you JUST comply with brake cooling requirements after landing, you may not be able to perform a maximum energy RTO without possible brake failure. Recent EASA criteria address this resulting in more stringent certification requirements. For the 787, the solution was to lower the BTMS scales vs. earlier aircraft - ie. a BTMS of 4 on the 787 might correspond to a 3 or less on a 777 or 747.

Is it okay to sometimes use idle reverse with no autobrake? Sure but there will be days/runways where it is not. Probably the reason why some operators are mandating use of autobrake is that landing performance will be more consistent and when you are trying to tailor your operation to the lowest common denominator, you will be less likely to have an over-run if everyone uses autobrakes, and even less likely if you require a landing performance calculation before each landing.

Regarding some airlines prohibiting the use of an autobrake setting of 1 on Boeings, I would question whether the increased brake wear is significant, especially in relation to the brake wear on a 15-20 minute taxi to the gate (on carbon brakes, brake wear is a function of number of applications rather than energy dissipated - something that to me is certainly counterintuitive). If minimum runway occupancy time is one of your goals, it may make more sense to use a setting of 1 if that gets you to your runway exit versus using a higher brake setting and then "crawling" down the runway to your turnoff (they love that at LHR).

[Al Murdoch]

Certainly my airline discourages AB1 on the 777 due to some issue with brake modulation causing problems at that setting.

[Skyjob]

Problem with AB1 is that the rate commanded is less than that achieved so initially it will come on, then release and do nothing, occasionally modulating is possible, until rate achieved by other means is not sufficient and AB1 will assist in remaining stop...

[JammedStab]

Is the reason for the brake modulation because the aircraft is already slowing down at the desired rate with the use of idle reverse and therefore brake application is only required sometimes due to the deceleration rate sometimes being above and then below what has been commanded by the autobrake system?

If so, then perhaps runway slope and wind could be factors and perhaps other reasons as well.

[piratepete]

BRILLIANT!

John, once again you create a very good technical discussion, well done as usual.There is of course no standard answer.It all depends upon the various factors, runway length, turnaround times etc etc, but I do remember the very very good landing/brake cooling techniques you taught me by demonstration after a high weight landing at NAURU (5000 feet long?) all those years ago, thank you Sir!

[BOAC]

I cannot see the problem with autobrake. As with everything in aviation, it requires some 'airmanship' or for those who dislike the term, common-sense, often sadly missing from those who write SOPs.

Autobrake is a superb tool in the box. With the tables I used on the 737 and an airport chart, planning for EXACT turn-offs was easy using autobrake (or not if not required....) and made the task of 'encouraging' the newer co-pilots to think about it much easier.

Once the run-out is established, a decision can then be made on use of reverse (noise/embargoes/brake cooling etc), but the autobrake distance will, of course not change.

All dependent. of course, on landing in the right place, but there's another story................

[alf5071h]

BOAC provides some perspective, but as noted elsewhere many aspects of airmanship are lacking, either due to poor personal endeavour or locked-out by an increasing culture of SOP adherence.
The latter includes an expectation that all circumstances will be covered, thus MFS activities might be of no avail; similarly the regulatory authorities shy from providing technical guidance whist placing greater responsibility on operators, and in turn operating crews.

The thread questions automation dependency, but greater use of automation is encouraged without deep understanding of the factors affecting use. Why do operators suggest that it is “less likely to have an over-run if everyone uses autobrakes”, we should not sink to the lowest denominator but seek improvement across the board.

Checking landing distance for every approach but is this a quick crosscheck of a table (or even a more believable electronic answer), or does it include consideration of the accuracy of reported runway conditions and wind, and thus the safety margin including variable human performance.

The UKCAA identifies many of the operational problems and provides ‘advice’, but often without the information required for understanding of how to apply ‘advice’ in operation.

http://www.caa.co.uk/docs/1428/20120...tedRunways.pdf

Landings during Winter Operations | Air Operations | Operations and Safety

[BOAC]

alf - "Checking landing distance for every approach" - a bit of over-kill there? I suspect Skyjob was looking at the "99%" routine landings which are conducted on familiar runways which are more than adequate (in good conditions) and where an 'early exit' is desired by ATC or taxi-routes? In these cases it is rarely necessary to spend too much time looking at 'runway conditions'/LDA since there is a more than adequate margin.

Obviously when things start to get 'tight' or 'dodgy' we need to take far more care (dare I mention 'airmanship'?) but as I say, 99% of the time, autobrake is an excellent tool for 'vacate at the second rapid exit' eg a 737 at LGW/LHR/CDG etc etc.