Operationally unnecessary use of autobrakes for landing

[Centaurus]

With reference to the Boeing 737 Series. That "Bible" the 737 Flight Crew Training Manual states: Use of the autobrake system is recommended whenever the runway is limited, when using higher than normal approach speeds, landing on slippery runways, or landing in a crosswind.

To me that is quite straightforward. And that is there is often no need for use of autobrakes for landings other than the above examples. Common sense would assume that the mention of crosswind implies strong crosswinds and not a few knots. Similarly "when using higher than normal approach speeds" should be taken as seriously high speeds such as all flaps up or partial flap and not simply because of headwind and gust additives which are considered as normal.

It is common to observe pilots using autobrakes for practically every landing regardless of runway lengths far in excess of runway limited. Even then few pilots elect to use less than autobrake 2. Autobrake 1 is almost unheard of. In the simulator we observe pilots using autobrake 2 as a minimum on a 10,000 ft runway and if landing with one engine inoperative they up it to autobrake 3 as if there is some urgency if landing on one engine.

Some time ago, I was involved in training pilots from a large Asian operator where it was company procedure to use Autobrake 2 for every landing. Local culture being what it was, pilots stuck literally to the letter of the law. The simulator session required an all flaps up landing on a limiting runway length. If ever there was an occasion for Autobrake Max this was it. But no, the manual said autobrake 2 for all landings and that is exactly what the pilot used. The result was a significant over-run at high speed off the end of the runway. Culture has a lot to answer for.

Granted, pilots are often constrained by company autobrake policy and have little choice. But one would have thought use of autobrakes increases wear and tear and thus increased cost. McDonald Douglas published an article many years ago called "The High Cost of Hard Braking" where it detailed the cost of each landing with and without autobrakes and where it discussed the lead-footed pilots that cost the company more money by their inappropriate braking technique. It suggested that accurate final approach and touch-down speeds as well as prompt use of reverse thrust often meant that braking use could be minimised. In other words the skill of the pilot in reducing braking to a minimum. The speed at which the brakes were first applied was an important factor in the cost of braking. The higher the speed the more wear and tear. Autobrakes are applied on the instant of touch down (high speed) although they back off to maintain a specific rate of deceleration with use of reverse thrust.

There may be occasions where a turn-off at a specific taxi way is needed operationally but even then judicious combination of reverse and manual braking means braking is at a minimum. Often braking is not needed until below 80 knots where energy requirements, and thus wear and tear, are less. Again, observations in the simulator have shown that pilots addicted to autobraking for whatever reason, when asked to use manual braking, tend to get quite rusty due to lack of basic skill required of manual braking techniques. They overreact by hammering the brakes manually causing jerking and oscillation of the aircraft as they try to maintain the centre-line.

Is this just another example of automation dependency where pilots have lost the skill and finesse of careful considered manual braking? Repeating the FCTM opening advice on autobrake use: "Use of the autobrake system is recommended whenever the runway is limited, when using higher than normal approach speeds, landing on slippery runways, or landing in a crosswind." Are pilots getting lazy or has the accent on braking automation led to pilots being apprehensive of their own ability to use manual braking? I suspect the latter...

[Willit Run]

The times they are a changing!

You would think that having an ATP rating would allow us to use common sense. Well, insurance companies and federal regulators have thought otherwise. It is funny that SOP's mandate us to use a minimum auto brake setting of 2 regardless of landing weight, runway length, or turnoff point.
But, when we have a very abnormal circumstance, which most of us have never encountered, we are allowed to use, ummmm,"our own judgement" because the performance computer can't come up with a recommended setting.

I recently flew with a very nice gentleman, fairly experienced, easy to get along with, and he punched up the recommended brake setting on the performance computer. It recommended a flaps 25, brake setting of 2 with regular reverse thrust. I said,we have a near 12,000 ft runway, a turnoff at the very end, clear calm night,perfect conditions, 100,000 lbs less than MLW, lets use no brakes, flaps 30, no reverse, and we'll be fine. The look on his face was priceless!

We are not allowed to use experience unless it is absolutely necessary, because our SOP's are lowered to the very lowest common denominator.
I'm still waiting for the FOQUA to bite me in the arse!

[jimmyg]

Quite to the contrary,

Many major legacy carrier recommend the use of autobrakes 1/Lo and idle reverse with thrust only as necessary. Much of this is due to the advent of carbon brakes and computerized braking systems. One even smooth brake application use of both left and right brakes make much more performance and economic sense. Which the autobrake system can accomplish to a much more consistent degree than the human factor. Also AirFase will flag a late braking event, which companies frown on.

High thrust reverse landings have only a small degree of stopping power and almost nil below 100kts, not to mention fuel burn, noise and the wear and tear on your most critical and expense asset.

Now of course, I whole heartily agree; that with a long rollout in the proper conditions, skillful use of manual braking and idle thrust is the way to go.

The use of real airmenship and knowing the difference between what the manual says and what should be done for a given scenario is fast becoming a lost art of our profession.

After all is this not what we carbon based units are supposed to be doing.

[compressor stall]

I believe the QF group mandate auto brakes for every landing.

I remember having a conversation with a QF skipper who was horrified that I would happily land on 16 at Melbourne (3600m!) with the intention to vacate at Kilo (i.e. the far end) with no autobrake and reverse idle.

For the record the Airbus FOQA flags the event red (Braking Delayed At Landing is the code from memory). Probably why some ops departments think that it's bad.

[de facto]

With reference to the Boeing 737 Series. That "Bible" the 737 Flight Crew Training Manual states: Use of the autobrake system is recommended whenever the runway is limited, when using higher than normal approach speeds, landing on slippery runways, or landing in a crosswind.
With reference to the Boeing 737 Series. That "Bible" the 737 Flight Crew Training Manual states: Use of the autobrake system is recommended whenever the runway is limited, when using higher than normal approach speeds, landing on slippery runways, or landing in a crosswind.To me that is quite straightforward. And that is there is often no need for use of autobrakes for landings other than the above examples.

You just omitted to add what is following your FCTM quote...which is:
For normal operation of the autobrake system select a deceleration setting.
Settings include:
• MAX:Usedwhenminimumstoppingdistanceisrequired.Deceleration rate is less than that produced by full manual braking
• 3:Shouldbeusedforwetorslipperyrunwaysorwhenlandingrollout distance is limited. If adequate rollout distance is available, autobrake setting 2 may be appropriate
• 1or2:These settings provide a moderate deceleration suitable for all routine operations.

Boeing recommends AB as you mentionned for limited runways etc as if you decide not to do it and use manual braking and get off the runway they will tell you :I told ya so!
Now it doesnt mean they recommend manual braking in other conditions..
Is this just another example of automation dependency where pilots have lost the skill and finesse of careful considered manual braking?
Are pilots getting lazy or has the accent on braking automation led to pilots being apprehensive of their own ability to use manual braking? I suspect the latter...

No,they use automatics when automatics are working and keep manual braking when situations require it.

Now of course, I whole heartily agree; that with a long rollout in the proper condition skillful use of manual braking is the way to go.
With a long roll out then you wouldnt have to touch the brakes in the first place,no?

[despegue]

De Facto,

I see often FO's who are totally unable to do a smooth braking themselves, are unable to coordinate deceleration to match exiting a certain exit etc etc.
All because too much use of the Autobrakes, even when it is unnecessary.

Use Autobrakes when landing on wet/contaminated, limited rwy or hard crosswind.
All the other landings: Autobrakes OFF and think for yourself and be a Pilot and not an Automatics Monkey:ugh::mad:

[de facto]

:mad:All the other landings: Autobrakes OFF and think for yourself and be a Pilot and not an Automatics Monkey

Despegue,hard wake up?:rolleyes:

Autobrakes OFF before landing is your prerogative,but before you jump my throat,i motivate my fos to fly raw data as much as possible and when situations allow it and if after landing they decide to use manual brakes to vacate using their deleration(ie AB chosen was too high ie landed shorter or AB was too low,landed longer than expected) then yes i have no problem and they will do it until its tiller time.
Ok for you?
I see often FO's who are totally unable to do a smooth braking themselves, are unable to coordinate deceleration to match exiting a certain exit etc etc.

I suggest you have a chat with your pilot management then...send an SRS!

[OPEN DES]

Airbus, my outfit:
Delayed Braking after Landing should only be triggered when idle reverse is not selected and/or is cancelled prematurely (i.e. Significantly above taxi speed)
In other words: an idle reverse landing with no brakes should not trigger a FOQA event.

As for the rest:
Agree with most sentiments here. Autobrake is a great tool, but manual brakes does the job a lot better in many situations. However a certain level of proficiency may be required.... ;)

[172_driver]

Then there are company SOPs that prefer the fuel savings of idle reverse over brake wear. Combined with another SOP - minimum runway occupancy time - you can literally end up with smoking brakes. But hey, we made the first exit!

[Jwscud]

My company (brand B) are autobrake advocates, with many Captains taking control at 60kts on the runway so many FOs get almost no chance to brake manually.

I also fly a more belts and braces type which lacks any auto brakes (or autothrottles, magenta line or VNAV) which has made me realise quite how mollycoddled one is in a modern aircraft. I use autobrake on the 737 because they pay me to, and because we spend a lot of time on short runways.

However, I flew many moons ago with a Line Trainer who had an old copy of the FCTM before the lawyers got to it, and its recommended braking technique was to progressively apply the brakes, only applying real force below 80kts as this was most effective and caused the minimum energy to be absorbed by the brakes.

[compressor stall]

In other words: an idle reverse landing with no brakes should not trigger a FOQA event.


Which Airbus type?

On my type the Braking Delayed at Landing FOQA event is triggered by the length of time to slow to 50kts after slowing 10kts from touchdown speed. It is invariant of Reverse selection.

And clarification to my above - it does also flag other colours, but it almost always ends up red if you have REV IDLE selected and no manual braking.

[despegue]

De Facto,

My mail was not an accusation towards you...I am quite sure that your abilities and technical knowledge is appreciated by those who fly with you, and those who know you on this forum.

[Tee Emm]

I believe the QF group mandate auto brakes for every landing.


True. That emanated from the Qantas Boeing 747 over-run at Bangkok on 23 September 1999 where, although the autobrakes were selected, they were inadvertently deactivated during the balls up after initial touch down. After that, the company went into ACM (arse covering mode) and directed that autobrake be used on every landing where autobrake was installed on type.

[Judd]

You just omitted to add what is following your FCTM quote...which is: From where I sit, the OP had no need to add the subsequent quote from the FCTM that you highlighted although I guess it all depends on personal interpretation.

Read the opening paragraph carefully. It states, among other things that "use of the autobrake is recommended whenever" etc etc. and gives a list of examples of when autobrake should be considered.

I read it as telling you that in the circumstances where the pilot elects to use autobrake for landing because of the operational situation of limited runway length, slippery runways and so on, then the FCTM amplifies or describes what deceleration rate can be expected with each setting. It does not imply that autobrakes are normal SOP for all landings.

[de facto]

despegue

Join Date: Oct 2002
Location: In my seat
Posts: 697
De Facto,

My mail was not an accusation towards you...I am quite sure that your abilities and technical knowledge is appreciated by those who fly with you, and those who know you on this forum.


Point taken and my bad,just got a whole month of verbal abuse in another thread:p

[alf5071h]

This thread highlights many of the significant safety issues in modern operations.
Manufacturers’ recommendations being interpreted as ‘must’ (legal overtones), the limitations of SOPs, poor wording or range of interpretations, none able to foresee every situation, all reducing the need to think.
Documentary dependency, with that of automation, boxes pilots into standard operating scenarios which reduce ability to deal with the unexpected, and in some circumstances creates new operational hazards.
Many areas of the industry believe that ‘that unexpected’ will not happen – to them or in their operation; they have no knowledge of ‘it’. Alternatively, an assumption that pilots will be able managed – overreliance on human intervention in abnormal circumstances.

A problem with autobrake, as with automation in general, is that it disconnects the pilot from the feel of the aircraft. Pilots lack knowledge of applied foot-force vs deceleration, and from that, varying decelerations on runways with different braking conditions. This is accentuated with the use of reverse.

“Use of the autobrake system is recommended whenever the runway is limited …”; what is limited?
Before stating the classic certification rules, how might a pilot judge this, what information is available in the QRH, what is taught, and does this result in a consistent answer?

As a predominantly non-autobrake user (most types did not have it), why do Boeing come to their recommendation; what are the problems in the various conditions. Historically the case was made on inconsistent human performance during an RTO – a rare occurrence with less safety margin than for most operations.
Perhaps Boeing now judges that automation can better human performance in more normal instances. Yet an operational interpretation of their ‘recommendation’ often opposes the Boeing philosophy that the crew can (will) always override. The expectancy is that crews will be able judge ‘when’ to intervene, but the recommendation reduces opportunity to gain those skills required to judge, particularly in the more abnormal conditions.

Has the balance between comfort, cost, runway occupancy vs safety swung too far? On the basis of overrun statistics arguably yes, – ‘safety first’; have we really thought about it.
Autobrake = automind; think about it, what does ‘use’ mean, assume, or imply - pilots, trainers, operators, regulators, and manufactures.

[Intruder]

I fly the 744, not the 737, but I think the concepts are the same, except for those specifically addressing carbon brakes on the 744...

First, I believe idle reverse should be used for ALL landings. There is little reason to use the brakes to overcome residual thrust, especially at high speeds. Keep the engines in reverse until you're ready to exit the runway, or until you'd have to add thrust to continue taxiing. The next time you hit ice on the paint stripes at the end, you'll be glad you picked up the habit...

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.

We use Autobrakes as a normal procedure. However, we also have a "hot weather" procedure which allows Autobrakes OFF on a long runway. Idle Reverse and no brakes (except for a brake check crossing 18/36C) is routine for me when landing on Rwy 09 at CVG, and other long runways where we roll out to the end.

[FullWings]

My company has no restrictions on the level of autobrake (0 --> max), only that a minimum of idle reverse is SOP on all landings. We also have to check the landing performance, not such a bad idea really? Then use auto brake (or not) and reverse to suit.

On the 777, AB1 with Reverse (full) can lead to increased carbon brake wear as the deceleration rates are not that different, so leading to the brakes coming on and off repeatedly.

alf, I agree with pretty much all you have said. As a Boeing pilot at the moment, we are just in the process of being provided with new QRH data which will have different factors applied. I’m not sure quite what this will look like but I think it might mean the end of test pilot stopping distances with corrections to apply, replaced with something more akin to real life. I’m awaiting with interest.

[safetypee]

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?

[FullWings]

I’m intrigued by the "hot weather" procedure.
From what Intruder has said, I assume there could be problems with a quick turnaround at the airfield in question with the weights he’s operating at. If you use reverse only on a long runway, you might need to apply the brakes briefly just before you vacate. Using autobrake, it will attempt to decelerate at a constant rate from main wheel spin-up, so putting a lot more energy into the brakes. If even the minimum auto brake setting will stop you in less than the LDA (or at the intersection that’s convenient), then you have unnecessarily dumped energy into the brakes when most of it would have been dissipated through drag/reverse in the rollout.

[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 :ok:
“…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/498034-new-landing-distance-calculations-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]

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!:D

[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!! :p

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 :sad:.
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]

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.



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]

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 :ok: 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/1428/20120801OperationsOnContaminatedRunways.pdf

Landings during Winter Operations | Air Operations | Operations and Safety (http://www.caa.co.uk/default.aspx?catid=2520&pagetype=90&pageid=14021)

[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.

[Jo90]

When my company added 767s (with carbon brakes) to our 757 fleet it was immediately clear that manual application of the brakes without an unseemly jerk was just not possible however feather toed you were. And autobrake application was just as uncomfortable at any setting from 2 up.
After much experimentation I discovered that if you landed with AB1 selected there was no snatch and a delicate squeeze on the pedals would allow you to brake manually as smooth as silk.
Within a couple of weeks of this discovery the company banned the use of AB1. Really annoying!

[Agaricus bisporus]

Its the extraordinary roughness of some pilots' braking that I find annoying, particularly the full-booted stomp to release an unnecessary auto brake, perhaps followed by complete relaxation of braking with another stomp of max effort at the turnoff.
One of the boons of auto brake is its smoothness. If you need it, deploy it, leave it to do its job and pickle it gently st 60kts or less. If you don't need it (can't brake manually like some, apparently?) leave it off.

Oh, and one other thing, the people who get half way down the runway on auto brake and then bury the neighbourhood in a fistful of reverse apparently unaware that it has no effect on braking distance...and then stomp on the brakes!

Pax comfort doesn't seem to feature in some peoples' books.

[Skyjob]

The full-booted stomp you describe is a system design.

To overcome and disconnect the auto brake a pressure greater than X psi must be applied to the toe brakes. This pressure on 737 is LESS than AB1.

When the full-booted stomp occurs you describe, it merely indicates that to disconnect the auto brake system, say 800psi was required by the pilot to be applied to the brakes but that the auto brake system was using (a lot) less than that pressure for the routine stopping of the airframe. So when the system disconnected, the additional brake force was immediately applied until the pilot was able to release his 800psi toes from the brakes.

Several techniques exist to different airframes to overcome this, the best one is to override the brakes when you know(!) in excess of 800 psi is applied by the brakes, e.g. when the reversers are stowed.

HENCE auto brake disconnect is the LAST item in Boeing's Landing Roll Out procedure, to avoid pilots inadvertently applying more brake pressure to disconnect the auto brake system than that used by the system itself.

At 60 knots, reduce reverse thrust to be at IDLE reverse when reaching taxi speed.
Approaching taxi speed, slowly move the reverse thrust levers to the full down position.
Prior to taxi speed, disarm the autobrake and continue manual braking as required.


Autobrake Selector
1, 1250psi, 4ft/s2
2, 1500psi, 5ft/s2
3, 2000psi, 7.2ft/s2
Max, 3000psi 12ft/s2 (below 80kts), 14ft/s2 (above 80kts)

There is an "on ramp" period where autobrake pressure is applied over a period of time. Approximately 750psi is applied in 1.75 sec, then the pressures above are reached in another 1.25sec for autobrakes 1, 2, or 3 and approx. 1.0 sec for autobrake MAX.

To cancel the autobrake on the landing roll with toe brakes you must apply a brake pressure in excess of 800psi.
This is more difficult on the NG's because the feedback springs on the brake pedals are stiffer.

[compressor stall]

Manual braking will definitely all be a thing of the past when Airbus' Brake to Vacate feature is ubiquitous…n:ouch:

[Bullethead]

I was taught years ago that to achieve a smooth autobrake disconnect that you only need to push on one brake pedal, not both, and then the deceleration you get is only half that of using both pedals and with no sudden 'bump'.

Still gotta keep it straight though.

Works well on all the Boeings I've flown and the Airbus I presently fly.

[stilton]

On the 75 /67 you can achieve a very smooth Autobrake disconnect by just nudging the speed brake forward a tad.


Beats the 'lurch' that's so hard to avoid with applying manual brakes to disconnect.

[Skyjob]

The lurch is easy to overcome, as posted above:

1) Ensure the auto brakes are applying pressure to the brakes by reducing reverse thrust to idle.

2) When reversers idle has been achieved, the brake pressure required to disconnect is less than that applied by auto brakes ensuring a smooth disconnect.

Note: failure to ensure pressure is applied to auto brakes results in the bump...

[FullWings]

I have occasionally asked the PM to alter the autobrake setting on the rollout if it turns out to be too much/little for the planned exit. Seems to work fine. Otherwise I slowly apply increasing brake pressure until it disconnects, then slowly decrease/increase the pressure as required. That avoids most/all of the discontinuity in deceleration that disturbs some passengers...

[B-HKD]

When my company added 767s (with carbon brakes) to our 757 fleet it was immediately clear that manual application of the brakes without an unseemly jerk was just not possible however feather toed you were. And autobrake application was just as uncomfortable at any setting from 2 up.
After much experimentation I discovered that if you landed with AB1 selected there was no snatch and a delicate squeeze on the pedals would allow you to brake manually as smooth as silk.
Within a couple of weeks of this discovery the company banned the use of AB1. Really annoying!

AB1 use is discouraged/prohibited at the majority of operators as in combination with reverse (even idle) it will result in brake modulation. This modulation significantly increases brake wear on the carbon discs vs. a constant, smooth application at AB2/3 settings.

[misd-agin]

What de-acceleration rate does the spoilers have? If it exceeds AB1 the A/B's don't engage until the de-acceleration rate slows to the AB1 rate.


Full thrust reversers and spoilers de-acceleration rate is approx. 2.75 at touchdown and decreases to approx. 2 around 100kts. That's how come, with AB2 selected, you don't feel them engage until below approx. 100kts if you're using full thrust reversers.


Someone mentioned keeping thrust reversers deployed until exiting the runway. The manufacturers have specific guidance for various engine/airframe combinations. It's often 'stowed by 60' or 'coming out around 60 to be stowed prior to taxi speed'. I'd go with the official recommendation.


Carbon brakes can be touchy but they can be smoothly manipulated. Early 767-200's were terrible and early 757's have that brake metering sponginess issue at low brake pressure.


The slower you are when you try to disengage the A/B's the bigger the lurch will be. Because of that I typically try to disconnect them around 100 kts(AB2 hasn't activated, AB3 is at approx. 1/3 rate- de-acceleration 2 is from spoilers/thrust reverser).

[Mikehotel152]

Let's say you select AB3 and then smoothly disconnect with the toe brakes just after 100kts, or use AB1 and then manually brake, how does one determine the correct brake cooling schedule?

In one case you have disconnected in order to reduce the degree of brake application and in the other case you are using more braking than the system would otherwise give.

[Intruder]

On the 747 you can use the brake temp indicators as a baseline for the cooling schedule.

[Skyjob]

Mikehotel152
Let's say you select AB3 and then smoothly disconnect with the toe brakes just after 100kts, or use AB1 and then manually brake, how does one determine the correct brake cooling schedule?

You cannot unless BTM is installed, as then any way you brake is irrespective as it is measured by temperature monitors which must not be read until 10-15 minutes after landing, after which brake release can occur for the determined time.

Most short haul operators do not have a BTMS and schedule turnarounds which would/could be adversely affected should any brake release requirement be established for XX minutes after 10-15 minutes on block as the turn around time does not allow for this.

The above mentioned operators rely on aircrew to plan ahead and apply correct braking technique reducing brake temperature rises by selection of proper amount of reverse thrust, deployed at the correct time and for the correct duration.

At least, that is thought in training and management, as on the line many pilots have no clue about brake cooling as the matter is never adequately explained, thus who could blame them if a higher ranking (training) crew member tells them "you do not need to use reverse thrust, it has no effect on landing"...

These pilots come onto the line not knowing any better and are a safety hazard for those crew flying AFTER them on the aircraft's next rotation as they leave the aircraft after their (e.g. 4 short sectors of) flying with all landings performed IDLE reverse and AB3, never releasing brakes to cool on stand in their turnarounds...

This threat can only be assessed by the next pilot by feeling the brakes or heat radiating from them. Remember cool to the touch requirement before subsequent departure? If you cannot touch the brake discs, they are probably still too hot between the discs internally at the friction layer.

Alternatively if the side wall of the tire is warm to the touch it must mean that the NOx inside the tire has risen enough to heat a layer of rubber through its entire depth. Caution should then be exercised as rubber is NOT a conductive material, thus these temperatures of NOx must have been significant to heat a layer of rubber.

[A Squared]

... mean that the NOx inside the tire ... thus these temperatures of NOx must ...

I don't believe that you'll find much NOx inside an aircraft tire, or you shouldn't anyway, if it's been serviced correctly. Aircraft tires are serviced with Nitrogen Gas, which is abbreviated N2, NOx stands for Nitrogen oxides which are combustion products.

[JammedStab]

On the 747 you can use the brake temp indicators as a baseline for the cooling schedule.

Manually disconnect the autobrakes on this type using brake pedals for every landing at various different speeds and have never experienced any sort of unexpected lurch. Perhaps they got the design right on this type.

[Skyjob]

A Squared, you are dead right, late post with fatigue

[laurent_avion]

There is a very interesting video on how carbon brakes work.

http://m.youtube.com/watch?v=SG4Aw5BujEU

And as a320 fctm states, the pilot has to reduce the number of brake applications in order to reduce brake wear. The wear is not dependent upon the pressure or time brakes are used.
Therefore, I believe autobraking system generally reduces wear, since you are using the brakes just once. And if you vacate at the last taxiway, you will probably use your brakes many times until your parking stand, thus increasing your wear.
Maybe those are the reasons why operational procedures recommend routine use of the autobrakes.

[JammedStab]

Actually, after looking a the video, we know that only 2% of brake wear is during the taxi-in because the brakes are hot. Therefore, while you are correct in stating that reduced brake events reduce brake wear, the brake wear is almost down to zero on the taxi-in. As stated in the video, approximately 20% of wear is during the landing(on average of course). And the most interesting part is that almost 80% of brake wear is during the so-called cold taxi when taxiing for takeoff.

[Centaurus]

And the most interesting part is that almost 80% of brake wear is during the so-called cold taxi when taxiing for takeoff.

JammedStab is offline Report Post


That being the case, to minimise carbon brake wear, isn't that a case for use of reverse idle while taxiing out in order to prevent excessive speed build up that would normally require brake application to keep the speed within safe limits? After all, the Boeing 737 FCTM does state that after landing "The thrust levers should be positioned to reverse idle by taxi speed" implying there is no problem with ingestion at reverse idle when taxiing.

[ANCPER]

Anyone,

Has AB procedure changed? I recall that brake fans were left on with a temp > 110 (the double band on the temp ind.).

[Skyjob]

We must ensure the differences between steel and carbon are understood including the taxi techniques.

Steel and carbon have different unique properties relating to brake wear and heating up/cooling down.
If properly understood the taxi technique differs from when using steel to carbon brakes.

Note brake fans are not fitted to many commercial airliners, when they are it is for good reasons, to be used...

Regarding leaving idle reverse selected for taxi, not a good idea, as forward thrust vectors are required on many occasions, to start or keep the aircraft moving. Is the author of the post suggesting pilots use forward thrust to start moving then select reverse idle while in forward motion and cancel the reversers thrust each time to use forward thrust again for its next requirement?

[alf5071h]

The European Action Plan for the Prevention of Runway Excursions (www.skybrary.aero/bookshelf/books/2053.pdf) discusses a proposed change to operational rules where the use of autobrake enables an exemption from the 15% additive to the expected landing distance (page 79).

Does anyone know if this proposal has been progressed; is any operator using this exemption?

The logic supporting the proposal is confusing. Previous paragraphs explain that the 15% margin provides some protection for the variability in normal operations – speed, flare, touchdown positon, reported runway condition, whereas the exemption suggests that the use of autobrake replaces most variability, although any difference in operation might only be the time and consistency of brake application.
The rationale states that pilots can always intervene when required yet fails to suggest how such a need be judged, or appreciate that max pilot braking might not make up any shortfall in landing distance if the landing was fast and/or long which the 15% margin might have mitigated.

[Centaurus]

Is the author of the post suggesting pilots use forward thrust to start moving then select reverse idle while in forward motion and cancel the reversers thrust each time to use forward thrust again for its next requirement?

Not at all. At idle reverse there is sufficient forward thrust from the hot end to keep the aircraft rolling at a satisfactory speed while the reverse from the fan deflection prevents too much taxi speed building up. While the engines are different (737-200 P&W) the use of idle reverse for taxiing on long taxiways such as Honolulu and Guam in the tropics was common practice keeping brake temps to a minimum. In fact the only time brakes were actuated was when stopping completely.

[Shem Malmquist]

Autobrakes are useful to maintain more constant pressure which will reduce wear on carbon brakes. However, one must be careful to not take them off, then "roll to the end" in a misplaced effort to "save the brakes" as that actually increases the brake wear. There is little training on this issue, but the difference between steel and carbon brakes should be understood (http://airlinesafety.wordpress.com/2014/04/03/how-to-get-the-most-out-of-carbon-brakes/) as Skyjob indicated above.

However, the caveat is that it depends on where you might turn off. If I need to get to a spot near the far end of the runway, I would leave them off and roll down to the end then plan a consistent application to attain taxi speed for the turn off rather than have autobrakes on by rote and then turn them off to roll down to the end. That is one application that is a waste of brake life!

[misd-agin]

If carbon brakes wear less when warm turning the brake cooling fans(if installed) on unnecessarily might lead to increased brake wear.


SOP's should address this.

[Shem Malmquist]

If carbon brakes wear less when warm turning the brake cooling fans(if installed) on unnecessarily might lead to increased brake wear.

Yes, might be a case of the left hand not knowing what the right is doing. We have seen this before. It is not uncommon also for those that write the manuals to not understand many of the nuances and not even know enough to know that they don't know, they just go on what has worked for them in the past. Too commonly, people rise to management positions that oversee technical aspects in procedures even though they do not have the technical background themselves, or it is extremely dated.

[keep_her_lit]

At my last airline: Memos from Chief Pilot would encourage minimum use of reverse, and maximum use of autobrakes.

Reverse uses more fuel, which comes from Flight Operation's budget, whereas autobrakes cause brake wear (Engineering's budget!)

:D

[Intruder]

Idle reverse uses little, if any, more fuel.

Whether or not you use Autobrakes is a matter of SOP plus the specific environment for each landing. If SOP says ALWAYS use them, then ALWAYS use them. If SOP says NEVER use them, then NEVER use them. Brake life considerations are then not yours, but the company's.

When you have the discretion to use them or not, simply have a general scheme in mind: Minimum runway/rollout length and/or maximum landing weight for NOT using them. Then when you get the performance data for the next landing, decide on whether to use them, which setting to use, abd when to revert to manual.

Know your airplane and its capabilities, as well as your own.

[Shem Malmquist]

Reverse uses more fuel, which comes from Flight Operation's budget, whereas autobrakes cause brake wear (Engineering's budget!)

I'm shocked. Truly...;)

[Judd]

If the braking efficiency of carbon brakes gets better the hotter they are, then is there an argument for deliberately "dragging" the brakes when taxiing for take off to heat them up so that in event of a high speed rejected take off the already hot brakes will permit greater stopping capability?

[Intruder]

No. I've seen a brake overtemp on taxi in a 744 due to a new guy with heavy feet taxiing the diagonal length of DFW...

On an RTO the brakes will heat up instantly. The brakes still have a finite energy absorption capacity, so deliberately heating them up in advance is NOT a good idea.