Reducing thrust in cruise for overspeed

[JammedStab]

Have never had to do it but it has been recommended to only reduce thrust levers to the mid-position. A friend recently told me that he saw someone bring a pair of CFM's back to idle once in cruise and the time to spool back up was in the order of 30 seconds or longer.

Has anyone seen similar(or better or worse) performance on other engine types?

[Mozella]

Has anyone seen similar(or better or worse) performance on other engine types?

Here's one data point (sort of). It's been a LONG time, so don't hold me to the exact numbers. I was qualified to do squadron level test flights on the U.S. Navy F-8 Crusader powered by a single P&W J-57, a conventional (non fan) turbojet engine with afterburner (reheat). These tests were done after major, squadron-level maintenance, like an engine change.

One test involved pulling the power back to idle at something like 40 thousand feet. We recorded the stable idle rpm and then set full military thrust; i.e. full power without afterburner. We timed how long it took to reach 100% and if I remember correctly the time was usually around 35 seconds or so. And the J-57 had a reputation for pretty good throttle response.

Based on that, I would guess the time for a high bypass fan engine to go from idle to high power at high altitude would be much longer than many pilots would imagine. I flew the 767 and I was always aware of the relatively long spool up time of those engines; however, I don't recall ever letting them stabilize at flight idle at high altitude and subsequently call for high power settings. But even so, thirty seconds or more doesn't sound unusual to me.

[framer]

I have seen the CFM-56's pulled back to approx 45% in cruise. It does take longer than 30 seconds ( maybe 40) to get back to 85-90%.

[safelife]

Use speedbrakes.

[RAT 5]

At high level it has been recommended to only reduce thrust levers to the mid-position.

Good idea, and use speedbrakes.



A friend recently told me that he saw someone bring a pair of CFM's back to idle once in cruise

Bad idea, unless you intend to descend.

[framer]

It seems unanimous then:)

[Kefuddle]

Do any of you 737 guys have the Engine Response Time Bulletin? There is a lot more to it, but it includes this about the cruise:
3. If the airplane experiences a sudden increase in airspeed that causes the autothrottle to reduce thrust, manually guard the thrust levers to maintain a minimum of 60% N1, if possible. If thrust is reduced below 60% N1, a significantly longer time will be required for the engines to spool up if the time at idle thrust is less than 60 seconds.

4. If the airplane experiences a sudden increase in airspeed, consider using smooth extension of the speed brakes to increase drag and to avoid large thrust reductions.

[vilas]

AIRBUS has given following procedures for overspeed.



OVERSPEED PREVENTION PROCEDURE



1.Keep AP and A/THR
2.Select a lower speed
3.Monitor speed trend
4.Speedbrakes (as required)



OVERSPEED RECOVERY PROCEDURE


1.Keep AP and A/THR
2.Full Speed brakes
3.Monitor IDLE or set thrust levers on IDLE

[john_tullamarine]

If the concern is Vmo, why are we so terribly concerned about reducing speed so quickly ?

Vmo is a limit but not of a "fall-out-of-the-sky" concern if one has a nominal exceedance ie bringing the indication back should be a more disciplined and steady operation.

[InSoMnIaC]

If the concern is Vmo, why are we so terribly concerned about reducing speed so quickly ?

Maybe because everyone hates paperwork

[Kefuddle]

If the concern is Vmo, why are we so terribly concerned about reducing speed so quickly ?

Agreed, but one should still one's best to avoid it without creating additional problems!

[john_tullamarine]

I empathise .. in my own fleet I have the same sort of problem with pilot concerns about exceedances and big brother ... we know about it from the black boxes after the flight ... even if I don't care much about this particular one, most of the pilots do, unfortunately.

However,

(a) folk should be aware than Vmo is not a full-on-must-fix-the-exceedance-before-the-plane-falls-out-of-the-sky sort of thing

(b) presuming the heavy iron folk still descend on the barber pole, modest/nominal Vmo exceedances are a routine fact of life.

[Kefuddle]

presuming the heavy iron folk still descend on the barber pole, modest/nominal Vmo exceedances are a routine fact of life.
I've never had the clacker in my thus far relatively short professional career. Any activation of the clacker is mandatory techlog entry, a call to maintenance and hopefully a deferred defect and authorization to continue.

[JammedStab]

I empathise .. in my own fleet I have the same sort of problem with pilot concerns about exceedances and big brother ... we know about it from the black boxes after the flight ... even if I don't care much about this particular one, most of the pilots do, unfortunately.

However,

(a) folk should be aware than Vmo is not a full-on-must-fix-the-exceedance-before-the-plane-falls-out-of-the-sky sort of thing

(b) presuming the heavy iron folk still descend on the barber pole, modest/nominal Vmo exceedances are a routine fact of life.

The problem is....some airlines treat an exceedence whether it is over landing weight by 1 pound or over VMO by 1 knot as almost the end of the world. As a pilot who can expect to be demoted or severely admonished, it becomes a big deal.

Any one else have any experience with spool up times at altitude, perhaps on engines other than CFM?

[vilas]

AIRBUS FOLKS
Over speed does not necessarily require inspection but pilots must report it. VMO>20KT or VMO and >2g requires inspection.

[ImbracableCrunk]

I flew with a CA recently who balked at my use of speed brake in mountain wave to avoid an overspeed. I told him about the "Bodie Maneuver" issue with N1 spool times and what the FCTM directs us to do.

His response, "I'd rather write up an exceedance than use speedbrakes in cruise."

[cosmo kramer]

I have done it once, and yes it takes forever for the engines to spool back up (in the order of 30+ secs is probably about right). However, I did have "forever" available, as with idle thrust and speed brakes out the speed was still increasing reaching a point well into the clacker (reaching almost .85 if I remember correctly).

Still in the clacker, I increased thrust as soon as the trend vector reversed and it took a long time to spool up, but an equally long time for the speed to decrease. But if you wait with increasing thrust, until the speed is back in the normal range you might set yourself up for a problem.

I agree 100% with john_tullamarine. It was a non issue, and no need to get stressed about. Just reduce speed calmly and no reason to panic. I could have started climbing, but it went so fast that the speed was already approaching .85 and the increasing trend vector starting to become less and expected to start reversing, that I didn't find it made any sense. My thinking was it was better to let it fly straight ahead, rather than to introduce G into the equation. The whole experience was unnoticeable, no turbulence, no previous warnings, no big changes in the wind was forecasted, no nothing. MMO is just a line drawn on a piece of paper in some manual that someone had to give an approval stamp. I can attest to that a 737 flies just fine at .85, and doesn't fall out of the sky or get's bend out of shape (in order not to be sued, I will however add the disclaimer "please respect the limits set out by the Boeing, and I assume no responsibility if you exceed them either inadvertently or on purpose"). :}

Had it been the other way around (decreasing headwind), I think it would have been a non issue, as the sheer was really smooth and gradual. I think the increase in thrust would have been much faster to hold the speed up. What I am getting at is, that the engines really spool down quite slowly too, which was contributing to the speed getting that high.

I would never let the thrust reduce to idle, for a small speed excursion, but in this case there was nothing else to do, and obviously with .85 there is a lot of time to before the speed decays to a critical level, to increase thrust again. For normal small increases in speed (like flying at .79ish having .815 and increasing trend vector), I recommend to start pulling the speed brake, before even touching the thrust levers - it usually works by itself. Due to the slow spool down time, speed brakes are much more effective (instant drag as opposed to slow decrease in thrust).

As for paperwork, it's one line in the Techlog, a 5 min inspection of the flaps and another line by the technician to sign it out again. And filling out a report, which takes 5 mins. No big deal really.

[cosmo kramer]

P.s.
I never heard a word from our safety department after sending that report. What kind of airline would punish their pilots for a weather phenomena out of their control?? Excuse me, but if I worked for such an airline, I would start looking for another job. That's a very poor safety culture, to have the employees living in fear of making a mistake and most like makes for an automation culture with inevitably decrease in skills.

[RAT 5]

His response, "I'd rather write up an exceedance than use speedbrakes in cruise."

This has got to be the first pilot I've ever heard about who would rather do paperwork after a flight than avoid it and be first in the pub. Amazing!

[172_driver]

Can testify to very long spool up times. I did it once when I was a new(er) first officer. It wasn't even idle, reduced to maybe 50 % N1 and it was painful to watch the slow response back up. A humbling experience and remember since the even humbler captain's suggestion to limit reduction to 70 %

[john_tullamarine]

I've never had the clacker in my thus far relatively short professional career.

One presumes your operation descends with a margin to the barber pole. No problem there. I'm a bit dated but we routinely had minor clacker exceedances (I'm talking 5-10kt rather than a significant exceedance).

Any activation of the clacker is mandatory techlog entry, a call to maintenance and hopefully a deferred defect and authorization to continue.

With the greater emphasis on DFDR/QAR exceedance monitoring, that makes good sense as it indicates attention on the flight deck and adherence to SOP. I would be extremely surprised if the base response was other than to continue.

some airlines treat an exceedence whether it is over landing weight by 1 pound or over VMO by 1 knot as almost the end of the world.

That, of course, is both true and most unfortunate. Unless those monitoring exceedances have a suitable engineering/certification background, there needs to be plenty of guidance from the totem pole folk as to what is, and what is not, terribly important in the overall scheme of things.

As a pilot who can expect to be demoted or severely admonished, it becomes a big deal.

Absolutely correct .. we all have our crosses to bear unfortunately


The main value of this thread is to get the acceleration deterioration at height message across to the general heavy aircraft pilot population ...

[Oakape]

Boeing have a current bulletin out for the NG, recommending that thrust not be brought back below 60% N1 for short term speed excursions & to use speedbrake if required.

The engineering manual at our joint requires a rather involved inspection for overspeeds greater than M0.02, which isn't much of an overspeed. It's 15kts for a VMO overspeed, if I remember correctly.

[who_cares]

I just recently had an over speed in the cruise CAS went from 247kt to 272kt (.85 Mach)in 3 seconds due to a 6deg temp drop in that time. Pulled the speed brake but speed was still increasing so also pulled thrust back towards idle. Yes it does seem to take forever for the engines to spool up again, but speed never fell below what was bugged.

[cosmo kramer]

Yes, you just got to anticipate when to add thrust again. Then it's no problem, i.e. NOT wait with adding thrust again, until speed is back at bugged speed, but rather as soon as the speed starts decreasing again.

And of course not overreact for small speed excursions as Boeing writes in their bulletin. Keep calm. Rather a little too fast, than a little too slow. ;)

[Machdiamond]

MMO is just a line drawn on a piece of paper in some manual that someone had to give an approval stamp.

I am with you in saying that it is not a fall-off-the-sky deal, but I wouldn't downplay it to that extent.

The margin set between MMO and MD (cleared for flutter and loads) is not based on the crew assumption that MMO is a rubber-stamped line.

[cosmo kramer]

I am not saying to disregard MMO, obviously. I am just saying that unintentionally exceeding it is no cause for panic (unless you work for an airline run by people that have no understanding of aviation and will use any excuse to punish you).

[john_tullamarine]

MMO is just a line drawn on a piece of paper in some manual that someone had to give an approval stamp

Vmo/Mmo is a limit the same as any other and is required to be observed. However, the limit has a lot more fat than the older style certifications using Vne.

Indeed, most (not all) AFMs have the rider that the limit may be exceeded for test or training.

[tdracer]

I was just reviewing a 747-8 AFM revision (something I need to do with some regularity), this is what it says:
"The maximum operating limit speed shall not be deliberately exceeded in any regime of flight."
I think the key word here is "deliberately".
BTW, 747 MMO is 0.90 Mach. During the 747-8 certification, I looked at a whole lot of data that was 0.97 Mach and higher (flutter testing and the such), and the airplane didn't break :ok:

[Machdiamond]

I believe a key differenciator for test pilots is that they act in a particular way when they know the first or even the second hole in the cheese is lined up already.
This is why you will not find MD published in the AFM.

[deefer dog]

Test pilot during acceptance of new aircraft demonstrated MMO exceedance. No big deal at MMO + 0.2, apart from noise of the damn clacker!

[framer]

This is why you will not find MD published in the AFM.
Yeah probably a good thing what with 1% of pilots being clowns and all.
Do Boeing and AB use the same process for determining MMO relative to MD?

[Kefuddle]

What is the term "MD" being referred to here?


Oops. Disregard. Just googled it. in case anybody else was as ignorant as me: Vd/Md are the absolute maximum speeds. I think referred to as dive speeds. 0.96 apparently for an A320, probably something similar for a 737.

[Capn Bloggs]

Maximum Mach in a Dive...

[vilas]

Kfuddle
A320 VMO350KTS, MMO M.82, VD381KTS and MD.89.
Only A380 has MD M.96
According Airbus
1. critical loss of lift due high Mach is well beyond the normal envelope and MD.
2. In level flight at high altitude, drag increase prevents MD from being reached. In flight tests MD is reached through specific manoeuvres (dives with full thrust are necessary)

[Kefuddle]

Thanks Vilas. So the difference between 0.82 and 0.89 isn't really that great considering the shear that can be experienced crossing a jetstream!

[cosmo kramer]

I think you overestimate the shear of even a very strong jet stream. Going from .79 to .85 (like I described previously) was a huge speed increase. And it took time. Had the speed continued to increase, it would have been fairly easy to pull back on the yoke an climb a bit.

Anyway, an Easyjet 737 was recorded to go 450 knots, in a botched manual reversion test. No damage to the aircraft afterwards! Though the Mach number was probably relatively low, as it happened around 10-15k feet, it is still a testimony, that these machines are stronger than what you might think.

[cosmo kramer]

And for those that think I am making that up/are not familiar with the incident:
The control forces remained high but the commander considered this to be due to the aircraft’s speed, which he observed at a maximum of 447 kt.
http://www.aaib.gov.uk/cms_resources.cfm?file=/Boeing%20737-73V,%20G-EZJK%2009-10.pdf

It's an interesting read...

[tdracer]

Deefer dog, I sure hope you meant +0.02 Mach, not +0.20 Mach :eek:


Most airliners don't like going supersonic :}

[Kefuddle]

Thanks Cosmo,

You're probably correct about my over estimation, it would be something like 40kt increase from 0.82. However, we know how astonishingly quickly things can unravel at 40,000 once problems occur.

Thanks also for the report, the FDM recorded max was an astonishing 429kts! This was quoted as Mach 0.719. I guessing the FDM sampling rate is the reason why the pilot noted a higher speed. Looking at this "Diving" Into A320 Diving Speeds (http://theflyingengineer.com/tag/vdmd/) the A320 Vd is 381kts, which must be similar to the B737!

Check you this video of the A380 flutter tests (https://www.youtube.com/watch?v=ImSuZjvkATw#t=294) (also at the end of the linked blog)

[Piltdown Man]

Speed brakes are not necessarily the best solution to an overspeed for all aircraft types. At highish levels, like 410, aggresive airbrake usage will easily take an aircraft like an E190 to the other end of the speed tape and beyond, without a significant change in airspeed. But reducing thrust to idle will provide relief. Fortunately, E190s have such small engines that they very quickly spool up to cruise thrust from idle.

PM

[Capn Bloggs]

At highish levels, like 410, aggresive airbrake usage will easily take an aircraft like an E190 to the other end of the speed tape and beyond, without a significant change in airspeed
I'm not sure I understand that. If you go to the "other side of the speed tape and beyond", your airspeed must be reducing, unless you are referring to the Vmin foot increasing when the boards are extended (as it does in my machine).

I would have thought acceleration rates of all pax jets would be the same (certification requirement). A slam accel from idle to max in an E190 or a 747 should be the same time?

[BluSdUp]

Hi All
I need to read all posts ,but one is for shure, speed is my friend and overspeed i can live with. Had a 25 kts plus transient clacker overspeed last year over ca 6 seconds in decend ca 30 000 feet never heard a peep.
Stalling after idle on a Cfm 56 will make CNN. 410 feet ca 41 sec pluss....
Longest in Your Log.

[Piltdown Man]

Almost Cap'n Bloggs. If the speed brakes are popped at high levels the Vma bar rapidly shoots up to (and if used too agressively, beyond) your current airspeed, without a corresponding reduction in speed. Thus they do little to reduce an overspeed but rapidly give you another one. It's not until you get down to 360 or so you can use them with relative impunity. Therefore, short of a climb (above the certified ceiling) there is little you can do apart other than closing the thrust levers to reduce your airspeed.

[JammedStab]

If the speed brakes are popped at high levels the Vma bar rapidly shoots up to (and if used too agressively, beyond) your current airspeed, without a corresponding reduction in speed. Thus they do little to reduce an overspeed but rapidly give you another one. It's not until you get down to 360 or so you can use them with relative impunity. Therefore, short of a climb (above the certified ceiling) there is little you can do apart other than closing the thrust levers to reduce your airspeed.

So would closing the thrust levers and then adding thrust well before the airspeed comes back down to the target speed make any sense?

[busav8r]

"Almost Cap'n Bloggs. If the speed brakes are popped at high levels the Vma bar rapidly shoots up to (and if used too agressively, beyond) your current airspeed, without a corresponding reduction in speed. Thus they do little to reduce an overspeed but rapidly give you another one. It's not until you get down to 360 or so you can use them with relative impunity. Therefore, short of a climb (above the certified ceiling) there is little you can do apart other than closing the thrust levers to reduce your airspeed."

Pitdown, I agree with you in relation to SB use. At very high levels it absolutely does not make any sense to use them :ugh:
But in relation to the thrust levers, why closing them considering the ATHR is engaged?! Why not just monitor the ATHR and see if it is simply doing is job?

What I teach to my students when flying at very high levels is:
1. Don't touch anything (which means, sidestick, thrust levers and SB)
2. Monitor the ATHR (and corresponding thrust reduction)

[vilas]

busav8r
If you fly Airbus you will be better off by following Air bus recommended procedures. There is a procedure for over speed prevention and over speed recovery and after recovery. It recommends use of speed brakes. For Prevention


1. Keep AP/ATHR on.
2. Select a lower speed.
3. Monitor speed trend.ar
4. Speed brake as required.
For recovery
1. Keep AP and ATHR
2. Full speed brakes.
3. Monitor idle or set thrust levers to idle.
After recovery
1. speed brakes as required.
2. Select appropriate speed. Keep a margin to VMO/MMO.
if manual recover smoothly and if ATHR is off adjust manually.

[busav8r]

Vilas, for your info this subject has been on discussion for quite long time now, and AFAIK many companies do not agree with this "new" recommended recovery procedure for the 320F. Airbus knows about this controversial and I believe they are studying it.

In my current company, there is a recommendation to not use the SB at very high levels (>350/360) and even at high levels it is recommended to use it with care.

This situation happened to me before and the final result was not brilliant. The use of full SB to a heavy weight 321 caused a small upset and the airspeed decrease was almost negligible.

Good luck.

[vilas]

busav8r
Airbus has put this as a procedures in FCOM on 8th Feb 2013. If the issue was before this then obviously they do not seem to agree and not following it could lead to problem with the authorities or is it after this date? What is A320F?

[Natstrackalpha]

My question re: the above learned comments for my tiny little mind is:


Can you not just Select an Airspeed on the FCU which is lower than the barbers pole and leave it there -


only - do it bit by bit say 5-10knots at a time.?

[Gretchenfrage]

I hope some of the contributors remember earlier lessons in meteorology where we all learnt that in wind-shear conditions (and that includes high altitudes!) the exedence to one side will most probably be followed by one to the other side.

Now where would you rather be, too fast or too slow, bearing in mind that you have to report either?

Congratulations, 65% of you answered right, they would rather be on the fast side. I can hardly remember one incident where an airliner crashed having been too fast but two recent and spectacular accidents having been too slow.

With some engines a pull back to idle is not a good idea, on others it is less of a problem, so know your aircraft.

But to use speedbrakes at high altitude is a no go on my deck. For how long did you guys experience an incidental overspeed at altitude and level? Isn't the aircraft somewhat autostable and the increase in drag brings you back in due time?
The Mach shock wave increases drag and reduces lift, the autopilot or the pilot will initially keep the altitude, therefore the speed will come back.
Extending the speed brakes will increase drag and reduce lift even more, the speed might come back more quickly, but the chances that the counter-shear will throw you into a subsequent low speed situation are greatly increased:

You are suddenly in an equally t&b-prone situation, but in a much more dangerous one. :ugh:

[vilas]

Nats
The Airbus procedure I quoted exactly says that. I believe that you should not make your own procedures on FBW because you do not have access to the computer logics. Any problems encountered in line operations must be referred to the manufacturer. After all they have the software, the hardware, wind tunnel and test pilots. They are in touch with the operators on a global scale. Serious issue like recovery from jet upset cannot be decided by consensus. Discussion yes by all means, to share what all happens up there. But solutions must involve the manufacturer.

[busav8r]

Vilas, I understand your point of view, but I believe this time you are not right. The airbus procedure maybe is adequate for lower levels but definitely not for very high levels. Like I said before, this comes from experience.

This situation cannot be "tested" in a simulator and I can assure you I already tried it in very different sim standards.

What puzzles me why worry using SB if the aircraft is in Normal Law (with all its marvelous protections). If the aircraft suddenly exceeds MMo, for sure this should be something related with a sudden change in OAT and/or wind. If the ATHR is engaged, it should do its job and the airspeed reduction should occur accordingly. If the ATHR it is not engaged, simply reduce thrust to T safe (50/60%).

Can you imagine (try to make an effort) if something happens (like what happen to the AF447) and while the SB are extended the plane suddenly downgrades to Alt Law? :ugh:

Once again, good luck.

p.s. A320F = A320 family aircraft

[vilas]

busav8r
While not trying to deny anything that you experienced I want tell you that there was a detailed presentation by Airbus during Flight Operations and Training Seminar of 2013 to discuss events reported by operators such as yours. It discusses the phenomenon in light of some causes, stage of flight and aircraft protections. Then they have explained the procedures. There two different stages. First is prevention when over speed is likely to occur, the next is recovery from actual over speed. In prevention speed brake is as required. Only in recovery from exceedance full speed brake is recommended. One reason for pilot intervention is limited auto pilot authority for passenger comfort. None of this is my suggestion so I am not right or wrong. My other point is about the authority of the procedure because should something seriously go wrong you can be nailed for not following the procedure. Also procedure that could affect safety should only be changed after consultation with the manufacture more so in FBW. I am fully aware simulators only simulate what is known thus far. So it is not going to help.

[PENKO]

45 seconds spool up time? Ok...
So what happens if you are at FL390 and ATC instructs you to descend to 370, will you never select OPEN DESCENT or LEVEL CHANGE? This will lead to idle thrust, Boeings and Airbuses do this on a daily basis, none of them fall out of the sky after trying to level off due to the thrust not responding.

[Natstrackalpha]

PENKO - Hi. you are right.


The FMGS will have programmed a spool up at that new lower level - and as you can see it would be bang on the numbers.
Also Thr/Idle (if that's the right one . ..) would command, as you know not total idle but thr idle. (a bit of thrust left in)


Airbussy logic prioritises airspeed over most other things, except RoC or RoD if Selected Vertical speed - therefore airspeed for your 2,000 descent is already in the bag in Managed Mode - usually, on that basis.


I think what the others are referring too - slowing a fast one down when in the past much older types have responded interestingly when a) taken out of autopilot and flown manually by the unawares of high speed high level flight


and


b) Sticking airbrakes up at high airspeed at high altitude.


Whats wrong with that? Well- as you already know when you are high your stall speed is higher - you go fast and you can come nearer to Mach crit, especially true of the old fogies like the 707 and the like not because they are Boeing, that great company but because of their old age design like other aircraft of various manufacturers of that time. also - other fun things at high altitude and high speed include consideration of Longitudinal Stability. Cruising high and fast is a time for being very aware and vary cagey - constantly monitoring the flight and staying away from the envelope edges.


Don`t know. Next time you are at Max Recommend consider trying it out.
before you do that - take a look down at the ground - just to see how high you are and then up at the Stratosphere - I am not being funny - I am being, on the ground, safe, with a nice cup of coffee.


I wouldn`t. - and you can ask me why - if you want . . . but rather take a look at this link - its quite cool.


http://www.skybrary.aero/index.php/High_Altitude_Flight_Operations#High_Altitude_Handling_Consi derations

[vilas]

NATS
Why do you think FMGS would not command total idle?

[PENKO]

I agree that idle is higher in the upper cruise levels than lower down. However, one would think that that solves the problem originally posted in this thread! Right? No longer spool up time because of the higher idle?

Anyway, airmanship, dare I say the word, dictates that you do not fully close the thrust levers when faced with a transient overspeed condition. That would be a gross overreaction (and not SOP on top).

[sonicbum]

PENKO - Hi. you are right.

Also Thr/Idle (if that's the right one . ..) would command, as you know not total idle but thr idle. (a bit of thrust left in)




NAT you are confusing between managed descent with Idle factor and open descent. In open descent you aways get thrust idle.

[vilas]

sonicbum
What happens to Idle factor in open descent?

[PENKO]

Regardless of the idle factor, when you pull open descent (or push managed descend when high on profile) you will get the same idle as when you manually chop the thrust levers!

So if that idle figure is safe for minor level changes, why is it not ok (according to the opening post) to close the thrust levers during an overspeed situation?

Again, I would be very careful with reducing thrust in high altitude level flight, but I do not recognize the dramatic spool up figures presented in this thread. Planes would fall out of the sky if things were that bad!

[Goldenrivett]

but I do not recognize the dramatic spool up figures presented in this thread.
Probably because ALT* gives at least 20 seconds of spool up time before ALT is annunciated.

[vilas]

PENKO
I was wondering why did you quote idle factor, even DES mode gives same idle unless it is flying repressurisation or geometric segment. I have quoted an official over speed procedure from FCOM. I am surprised people want to device their own procedures in FBW aircraft without referring it to AI.

[cosmo kramer]

So if that idle figure is safe for minor level changes, why is it not ok (according to the opening post) to close the thrust levers during an overspeed situation?

Again, I would be very careful with reducing thrust in high altitude level flight, but I do not recognize the dramatic spool up figures presented in this thread. Planes would fall out of the sky if things were that bad!
For Boeing, I can assure you that the spool up time is in the order of 40 secs plus. The EEC changes the spool up time depending on various circumstance:

Analysis of these reports indicates that this is related to the Electronic Engine Control (EEC) software revisions 7.B.U1 and 7.B.V2. Revision 7.B.U1 reduced the engine deceleration and acceleration rates for specific thrust lever transients at high altitude. Revision 7.B.V2 returned the deceleration rate back to normal but retained the reduced acceleration rate. Both versions of the EEC software reduce engine acceleration rate if the throttles are in idle for less than 60 seconds. Slowing the acceleration rate of a heat soaked engine improves engine operability (stall margin) characteristics.

I would advice against using LVL CHG to descent from FL390 to FL370, as you mentioned as an example. Alone from the fact, that it would cause a high rate of descent which may cause nuisance TCAS alerts. If doing so anyway, the ADFS would anticipate the required time to spool up the engines, to level off on speed.

[cosmo kramer]

And as for using speed brakes (not just for overspeed, but also undesired speed increases inside the operating limits), Boeing writes:

If the airplane experiences a sudden increase in airspeed, consider using smooth extension of the speed brakes to increase drag and to avoid large thrust reductions.

I don't, in anyway, share the opinion of Gretchenfrage. There is no problems using speed brakes during cruise what so ever (of course while keeping the hand on the level and the eyes on the airspeed indicator).

[sonicbum]

sonicbum
What happens to Idle factor in open descent?

If you read my previous post carefully, you will get your answer.

[PENKO]

Vilas, I did not introduce idle factor in this discussion :ok:

Probably because ALT* gives at least 20 seconds of spool up time before ALT is annunciated.

Golden Rivet, what about when you are flying manually and leveling off: Do you really anticipate a twenty+ second spool up?

[cosmo kramer]

PENKO, my answer in post 63 was for you. If in manual flight (Boeing) and not spooling up the engines EARLY, when leveling off (and with less than 60 seconds idle time) - you are setting yourself up for troubles, i.e. a serious under speed condition.

If you e.g. keep the throttles closed and aggressively pitch up to stop the descent (passengers and flight attendant won't be happy). and THEN reapply thrust. AFDS doesn't do it that way. It goes into ALT ACQ and slowly reapply thrust and slowly increase pitch, so that everything comes together simultaneously (holding altitude, having correct speed and thrust).

If you are lucky (as most times during the descent you are light), you will still have a big speed range to absorb the under speed, if you have to descent for traffic while still heavy, you are worst case setting yourself up for a stall recovery or and embarrassing request to continue the descent.

[LNIDA]

I fly the NG on some of the longest sectors operated by any Boeing NG operator in the world DBX/OSL & TOS/LPA/TFS we routinely leave the ramp at 79.2T (MTOM 78999) high altitude trips down to the Canary isle will often cross multiple significant changes in OAT/wind direction and we need to get high to get the endurance. My routine is bank angle selector 10/15 and MAX CON on limit page.

I'm not in the least concerned about filing a report for an exceeding a limit, but I'm very nervous about getting slow the FMC generated fast/slow limits are all based the aircraft mass being the 'actual' aircraft mass we often use a mix of charter weights/actual baggage weights/standard baggage weights, we sell an allowance of 20kg bag weight yet use an average of 13kg so a 100 bags could put your actual 700kg above your paper weight, for this reason i will not go above the FMC generated OPT flight level unless I'm very sure the wind and temp are stable and i always aim to be at least 1000' below the FMC generated MAX flight level.

I have only once seen the aircraft come back to the top of the slow box following a temp change and even with 100% we could not get away from slow box and had to descend.

The auto throttle logic on the NG is very slow to reduce thrust, much quicker to add thrust and with rapid speed increase due to wind/temp will likely result in an incursion into the barbers pole zone, there is ,if i can find it a Boeing bulletin on this subject with a warning that thrust recovery can be very slow when slowed to F/I at high altitude. It will be interesting to see how the B738MAX fares in this regard given my companies intent to use them on 8 hour + sectors across the ITCZ !!!

Small level changes will not normally result in flight idle thrust, in any event the aircraft pitch will pitch up as it starts to acquire the new altitude and increase thrust so by the time its back in level flight thrust will be at required

NSB 38 covers this subject, in short if thrust is reduced to F/I for less than 60 sec then the EEC software reduces the acceleration rate of heat soaked engines to improve stall margins, guard the thrust levers from reducing below 60% below this figure spool up time will be much longer with a possible speed loss above 20-30 knots, this only applies above FL300, if the thrust levers have been at F/I for longer than 60 sec then acceleration of the engines will be normal

[cosmo kramer]

LNIDA, so I guess this would make you uncomfortable? :)

I took those pics for this thread, where MAX ALT was discussed to death:
http://www.pprune.org/tech-log/524297-mct-cruise-5.html

I fly 737-800 (26k engines) at MTOW too (long distance and/or often takering sectors fueled to MTOW).
http://s23.postimg.org/p3kfmk5sr/IMAG0143.jpg

http://s9.postimg.org/soqbuyuj3/IMAG0144.jpg

[LNIDA]

Been there done that

But as i said it all depends on the day and as i also said i'm less concerned about the overspeed condition, but anyway why push it? you might have someone in the other seat with little or no high altitude experience, so your sat there with a 9 knot margin and you take a toilet break, next minute chummy gets overspeed and out go the speed brakes and back comes the thrust, probably something he/she as never seen before, meanwhile your stood by the door (wrong side of) awaiting chummy to follow the correct procedure to let you back in.

Having looked at the CRZ/thrust/weight tables either our brand new aircraft are heavier than we think or have more drag than Boeing thinks

If you were flying above the FMC MAX ALT in our company and caught at it you'd be off the line, these limits & restrictions are there for the safety of the passengers and crew, in any event flying above OPT is normally counter productive unless your on a speed limit due slower traffic ahead at your OPT level

So never mind me being uncomfortable, why make your colleague feel uncomfortable? CRM is all about team work,with me i think you'd be flying single crew on the next sector, although it sounds like you fly single on all of them:rolleyes:

[cosmo kramer]

So never mind me being uncomfortable, why make your colleague feel uncomfortable? CRM is all about team work,with me i think you'd be flying single crew on the next sector, although it sounds like you fly single on all of them :rolleyes:
Why get personal. I didn't ask you if you are the type that always brings a ton extra fuel "just to be sure", although one might get the impression from "i always aim to be at least 1000' below the FMC generated MAX flight level"... Where did you get this arbitrary 1000' from?

in any event flying above OPT is normally counter productive
Not more counter productive than flying below. And there may be environmental benefits as well, that speak for choosing a level different from optimum, like more favorable wind etc.

It's really off-topic, but I just can't stand such unfounded personal margins. If Boeing wanted you to always operate at max alt minus 1000 feet, and deemed it unsafe to go higher, they would simply have programmed the FMC to show max alt 1000' lower.

[RAT 5]

Is it not the case that Max Alt is affected by the CRZ C of G% in the FMC. The default is 5% and is the worse case. The actual MAC will tend to be very much more. Inserting the correct number will raise the Max Alt displayed and that is the real aerodynamic Max Alt. Some companies allow the actual to be inserted, others maintain the default 5% for a buffer margin.
Further, is it still the case where FAA & JAA had different 'g' margins at CRZ levels? I think it was the case where FAA allowed 1.3g buffer & JAA wanted 1.4 or 1.5g. Correct if wrong.

[rudderrudderrat]

Hi Rat 5,
Inserting the correct number will raise the Max Alt displayed and that is the real aerodynamic Max Alt.
You should have the correct number inserted into the FMC from load and balance calculation.

On a previous type we were permitted to reduce the buffet margin from 1.3 (max 30 degs bank) to 1.2 (Max 15 degs bank) provided there was no turbulence forecast ahead. By using fuel distribution graphs, we could insert a new cruise C of G figure which then displayed a new MAX FL.

[LNIDA]

Cosmo not personal at all, but i spend a lot of time training pilots to adhere to company procedures and along comes someone who makes it up as they go along, there is no doubt your knowledge is deeper than average and to answer your other question i take the fuel required no more no less, the required being what i need to operate the flight safely sometimes that is plog fuel sometimes more and sometimes less (our plots use longest SID/STAR)

If the FMC entered mass is correct i.e. actual then the FMC will normally provide you with the most efficient CRZ level taking into account fuel burn, maintenance, & so on, our company guidance is that a 1000 below OPT is normal preferable than a 1000 above and we have had 2 high level upsets.

My point about CRM is simply that every time an F/o comes along and says "well I was flying with Capt Kirk and he said the FMC figures are guesses/rubbish/tool/just a guide" and guess what its the same names that keep cropping up, anyway enough drift

We are all agreed that reducing thrust at high FL to idle is not good and that gentle application of speed brake is what the manufacture recommends to address transient unintentional over speeds :ok:

[Kefuddle]

It's really off-topic, but I just can't stand such unfounded personal margins.No offence to Linda because my agreement with Cosmo does not reflect on his protagonist, but :ok: Where does lack of confidence in one's abilities or the aircraft's capabilities end once on this rocky road?

[No Fly Zone]

Unless I'm missing something kida-really big, the take home is to make at-altitude power adjustments slowly and gently, even when planning to descend. Cannot think of a good reason to chop from 93% to idle in one pull. If one needs to descend rapidly, point the SOB down, use speed brakes and reduce power, but gently. Even if one needs to head down quickly, i.e. pressure loss, the last thing you want is loss of one or more pulling gizmos! do it gently, use the speed brake and point it down. It it is still flying, maintain what you've got, slow a bit, point down and consider your options. Except in an RTO situation a zero AGL, I cannot imagine a good reason to chop from high to idle in two seconds. Again, am I missing something?

[cosmo kramer]

My point about CRM is simply that every time an F/o comes along and says "well I was flying with Capt Kirk and he said the FMC figures are guesses/rubbish/tool/just a guide" and guess what its the same names that keep cropping up, anyway enough drift

And you know what? I have the exact same problem! When I ask an F/O to request FL390, I have to go into a long explanation why it isn't necessary to ALWAYS have max alt plus 1000', 600' or at the very least 400', before initiating a climb, and explain that Capt Lnida's personal limits have nothing to do with Boeing procedures.

Except for the barber pole and the minimum speed (which is taken from air data), Capt "Kirk" is right (isn't Kirk always right by the way? ;) ). Everything the FMC puts out are best guesses. You see my margin as 9 knots. I see my margin (for the VERY worst case) as 203 -267 = 64 knots (of course fluid with the load factor induced on the aircraft by turbulence).

With "VERY worst case, I am talking about the extremely unlikely event (that will happen 2 times in a career), where due to a strong sheer I end up in deep in the yellow and unable to pull out. To clarify, I never allow the speed to get into the yellow band.

But those few times in a career where it might happen: I will rather say "xxx, descending, unable to maintain altitude, call you leveling off".
...and operate the rest of my thousands of flights efficiently. :ok:

I assume you agree that the minimum maneuver speed yellow band, isn't aerodynamically dangerous per se, but when going in there it's just a reduction of your margins? I also assume, that your real concern is rather lack of sufficient thrust? I also assume (given the description of your ops) that you have 26k or 27k engines. Those factors together Boeing addresses with the following:
FCTM:
On airplanes with higher thrust engines, the altitude selection is most likely limited by maneuver margin to initial buffet.

You are founding your personal limits by ONE bad experience. Which wasn't even that bad: You just descended and regained speed and probably climbed back up a little bit later? Sure, you had to take a break from reading your newspaper and your adrenalin level might increased a bit, but was this a near disaster?

It's a bit like someone experiencing a decompression refusing to fly above FL100 again, because he never want to have to do another emergency descend. :}

[LNIDA]

Yep you got it in one thrust limited, the problem with your approach is that when do you say that's high enough?? so FMC MAX ALT 384 you happy with 390 to CRZ after all what the FMC says is just a computers best "guess" based on all of the parameter YOU have entered plus the inputs from the AD.

It just don't get your point here, my margin is not a random personal all I was saying is that if forecast shear and large/rapid temp changes then i feel a little caution is safer than pushing all the way up for often no benefit other than WoW look at me I'm at FL410 and if your sat there at 100% to stay out of the yellow box you'll be burning more of YOUR companies fuel than i will be a few 1000ft below.

Lets leave it at that and agree to disagree. :ok:

[Goldenrivett]

what about when you are flying manually and leveling off: Do you really anticipate a twenty+ second spool up?

PENKO, I anticipate a much longer spool up time. I would not be descending at 3,000 ft per min with 1,000 feet to go. I'd be aiming for around 1500 ft per min or less which would give me at least 40 seconds to level off.

What sort of RODs to you have with 1,000 ft to go?

[PENKO]

Goldenrivet, with or without the AP? I have no set numbers in mind for ROD. Since we are not allowed to fly manually anyway in RVSM.
Don't get me wrong, I do appreciate that the spool up time is much higher, I just doubt the dramatic numbers stated in the beginning of this thread.

Let's put it differently. Occasionally I've had to arrest the descent instantaneously on request by ATC I can't remember having had any significant troubles with the spool up time vs. level off... but hey, I'll keep my eyes open next time!

[framer]

I just doubt the dramatic numbers stated in the beginning of this thread.
It is over 40 seconds for a CFM to spool up from idle at FL 370 with ISA conditions. I've timed it.

[flyingchanges]

It is over 40 seconds for a CFM to spool up from idle at FL 370 with ISA conditions. I've timed it.

100% correct, longest 40 seconds I have experienced.

[tdracer]

It is over 40 seconds for a CFM to spool up from idle at FL 370 with ISA conditions. I've timed it.

A little good news, my counterpart on the 737NG tells me that 7.B.W EEC s/w will improve the accel characteristics at altitude. Should certify this summer.

[cosmo kramer]

LNIDA:
It just don't get your point here, my margin is not a random personal all I was saying is that if forecast shear and large/rapid temp changes then i feel a little caution is safer than pushing all the way up for often no benefit
Yes caution is in order if in actual turbulence or if it's forecasted ahead.

But, NO, that was not what you were saying before:
LNIDA:
i ALWAYS aim to be at least 1000' below the FMC generated MAX flight level.
But, I am happy if the discussion changed your mind a bit. :ok:

LNIDA: FMC MAX ALT 384 you happy with 390 to CRZ after all what the FMC says is just a computers best "guess" based on all of the parameter YOU have entered plus the inputs from the AD
I play with the computer instead of letting it play with me:
http://www.pprune.org/tech-log/524297-mct-cruise-6.html#post8096769 (post 108 if the direct link doesn't work).
If you don't care to read it, let me ask you: What factors determines the MAX ALT? Which one can we be certain of? And which ones are uncertain? Which ones are factual? And how do they individually affect your max alt?
I can think of one example where I would have no problem climbing to FL390 with max FL384 (or lower) show... It's in the post that I linked to. :)

[Kefuddle]

Cosmo,
I can think of one example where I would have no problem climbing to FL390 with max FL384 (or lower) show... It's in the post that I linked to. :)Do you have a procedure to modify the cruise CG? We don't unfortunately, but when it is changed from the default 15% to probably a much more realistic 19-22% the max alt 'magically' increases significantly :D

Sorry about this, but from that other thread:
...I select CON when I need to. And I do so routinely due to the way I operate the aircraft...In fact, I always select CON with a <15 knots window.
However, I do not set CON routinely, only when I suspect it might actually be needed inline with the FCTM and the recent Bulletin. I don't see any specific issues with CON mind, just CRZ is the intended thrust limit for cruise and I prefer to operate these strategies with specific criteria in mind rather than get into a routine that is, strictly speaking, a deviation - however trivial or slight (or non-existent in impact) that deviation may be.

[LNIDA]

My whole point about crz level was on very heavy aircraft crossing temp/wind zones and the sudden narrowing of the overspeed/under speed margin.

Our EFB provides us with a very accurate MAC because we use allocated seating and know where the passengers are seated re zone a,b,& c we subtract 4% from the MAC for FMC perf page and can re calculate inflight after fuel burn off if necessary

This from Boeing FCTM
Maximun Altitude

Maximun altitude at which the aircraft can be operated, It is determined by 3 basic characteristics (for each model) The FMC max altitude is the lowest of

. max certified altitude

.thrust limited altitude - the altitude at which sufficient thrust is available to provide a specific minimum rate of climb (depending on the thrust rating of the engines), the thrust limited altitude may be above or below the manoeuvre capability

. buffet or manoeuvre limited altitude

Although each of these limits are checked by the FMC , available thrust may limit the ability to accomplish anything other than relatively minor manoeuvring. The amber band limits do not provide an indication of manoeuvre capability as limited by thrust.

NOTE to get the most accurate altitude limits from the FMC ensure airplane weight, CRZ CG and temp entries are correct

You provide some interesting and thought provoking comments and i always welcome that from anyone, but you are in my humble opinion acting in a manner that at best will confuse and more likely intimidate your co-pilot, i would be very interested to know if your company procedures allow you to do this and exceeding the FMC derived maximum altitude its is done with blessing of your pilot/training management? the fact that the aircraft may be able to achieve it secondary to the limitations and what do you suppose would happen to you and your co following an high altitude upset where upon the FDM showed that your were above the max altitude? the reason for the upset is not relevant but if there were injuries arising from the recovery then i suspect the lawyers would have a field day, so why Capt Kirk did you think this was a good idea?

Don't get me wrong, i don't doubt that you are a committed and experienced Capt but the fact that your F/o's are having to be re educated by you on the subject of high altitude flights suggests either your training department is at error or dare i suggest it without offending you that perhaps you should reflect upon your own style of operation

Either way fly safe 41'000 is for biz jets or big aeroplanes with big donks :cool:

PS the next update of the FMC will provide a thrust limited altitude for manoeuvre

[PENKO]

It is over 40 seconds for a CFM to spool up from idle at FL 370 with ISA conditions. I've timed it.

It must be a Boeing thing then. At FL320 on the Airbus it takes more or less 15 seconds. Reducing speed at FL380 from M .78 to .72 commands idle thrust...and the thrust comes back on decelerating through .74

[cosmo kramer]

LNIDA, no I wouldn't go above max alt, as displayed by the FMC.

What I was trying to get at, was which input the FMC uses to decide on these limits. One that is oft forgotten is the selected speed. The FMC doesn't calculate the max altitude, based on the most optimum speed for that level. It uses the speed you have already select (or cost index you entered), assuming you will want to continue with this speed at the next level.

If this speed is very high or very low, the FMC will show you your max alt lower, than what the aircraft is capable of, if you change your speed. Hence, I can get the FMC to SHOW a very low max altitude, but still climb safely above it. Of course I would change the input to show something sensible before actually initiating the climb.

THIS is what my point is, an extra xxx feet becomes arbitrary, if you don't consider what input is behind it. My only concern is instead this:

"How big is my speed window in the new level." In smooth air my personal limit is 10 knots between the low and high speed maneuver band. In turbulent air, I might want to see 30 or 40 knot, which may be an even bigger margin than your 1000 feet. The difference is, I know what I am getting, and you are not.

By using the FMC, like I described in the other thread in post 108, you will always know exactly how big your speed window is, regardless of other factors. Still of course your weight, cg and temp needs to be fairly accurate.

If you are bored in cruse on you next flight, play around with the values to see how much e.g. a ton extra ZFW, moving the CG 5 units etc. affects your margins. If you suspect the aircraft to be heavier, than the values on the load sheet, you will the have a feel for how many knots that actually change on your margins.

A good eyeopener for a new F/O is to increase the ZFW with 10 tons. At first they see the and unbroken yellow band from minimum speed to MMO, they become a little wary. But after a few seconds, when they see the aircraft doesn't care and happily keeps flying, they become relaxed and and realize that what the computer says doesn't aerodynamically affect the aircraft. Garbage in garbage out. It's still just a stupid computer and the reality of nature determines if the aircraft will fly or not. And no, I don't don't do it to bother them. ;) But to increase their confidence in what they see and feel is more real that what the computer calculates.

PS the next update of the FMC will provide a thrust limited altitude for manoeuvre
The FMC already consider thrust limited altitude based on a residual rate of climb of 300 fpm in the climb and 100 fpm at cruise using LRC tables.

[LNIDA]

I think your speed spread dependant upon conditions is entirely reasonable and i have also played around with the ZFM and as you say it is interesting to see the yellow bands close.

I want the FMC input data to be as accurate as is reasonably possible.

I am aware of an aircraft that departed with the correct v speeds from an EFB but a -10000kg figure in the FMC which then told them they could go straight to FL410 needless to say despite trying they didn't get there oops

The FMC does consider thrust limited altitude, but the amber band limits do not provide an indication of manoeuvre capability as limited by thrust. The next software release will correct that.

My last comment on the subject.....promise

[cosmo kramer]

My last comment on the subject.....promise
Thanks for the discussion, I enjoyed it. :)

[OSCAR YANKEE]

"I'd rather write up an exceedance than use speedbrakes in cruise."

Could not agree more.
Have seen quite a few overspeed-in-the-cruise-reports for the A320 over the years, and people intervening - reducing thrust, speedbrake, lifting nose etc. almost invariably make the situation worse.
The A/C is a completely different beast at cruise level, and people are not used to it.
As earlier mentioned no inspection is required if exceedance is less than 20 kts (and I have never seen one higher) , so let the A/P+A/T sort itself out, and write the ASR........

[cosmo kramer]

As earlier mentioned no inspection is required if exceedance is less than 20 kts
Of curiosity, do you need to make a tech log entry? And if so, can you sign it out yourself.

On Boeing it's a mandatory tech log entry, and only a certified maintenance technician can sign it off. Hence, an AOG item when flying to a remote airport with no maintenance.

P.s. On Boeing it's a non-issue to use speed brakes.

[vilas]

OSCAR YANKEE
The autopilot ATHR may not sort it out itself and could lead to more complications. Less than 20KT no inspection is required but crew must report it. The procedure mentioned in my earlier post is given in FCOM:


OVERSPEED PREVENTION

Ident.: PRO-ABN-10-00014874.0001001 / 08 FEB 13

Applicable to: ALL

A318/A319/A320/A321 FLEET PRO-ABN-10 P 11/20

FCOM ← D to E 06 MAR 14
OVERSPEED RECOVERY

Ident.: PRO-ABN-10-00014875.0001001 / 08 FEB 13
Applicable to: ALL
FCOM page F

QRH only gives the recovery procedure.
Abnormal emergency procedures ABN80.06A

[RAT 5]

I want the FMC input data to be as accurate as is reasonably possible.

I suggest it is time to consider increasing the, IMHO, rather ludicrous low ICAO standard pax/baggage weights. It could well be that on a full 189 seater a/c you could be 2 tonnes heavier than the load sheet tells you. If all male, full baggage at 20kgs, it will be much more.

Regarding the CRZ MAC, it seems some companies allow you to insert the actual number, others forbid it and stay with the default 5% (B737NG) for a safety buffer. Going up to absolute max alt and reducing to 1.2g if no turbulence is forecast is really taking TEM management to the limits. The forecasts are made hours in advance by computer models and differ depending on the meteo centre who made them. Their accuracy is unreliable. I say this because I've been through areas of forecast turbulence with nothing, not even a cough. If that is the case then the forecast of no turbulence must also be questionable; although the met forecasts in all cases e.g TAF's etc. seem to be always pessimistic. I thought we were in the risk avoidance business.

[OSCAR YANKEE]

@vilas

I am well aware of the advice in the FCOM.

My opinion is strictly personal, but is based on having read the reports, and seen the flight data from those reports where people have used speedbrake, idle thrust, lifting the nose etc.

Airbus has to give advice like this, because they cover any overspeed.

I dont think my company has seen any excursions higher than 6 knots in the cruise, and the observations were quite clear.
People exacerbated the situation by intervening, and you were left with the sensation that they would have been better off just leaving the A/P+A/T to sort itself out.
(However you cannot know of course, it is speculation, albeit qualified.....)

[Gretchenfrage]

My opinion is strictly personal, but is based on having read the reports, and seen the flight data from those reports where people have used speedbrake, idle thrust, lifting the nose etc.

OY, I fully agree.

But we have to realise that we are of a dying species, the one with experience and some common sense left. We are overwhelmed by the new generation who religiously follow the magenta line, the FCOM and SOPS without filter or questions.
Remember the former UAS by Airbus, that was amended after some incidents? It shows that not everything straight from the A/B horse's mouthes is incontestable and of final wisdom.

[vilas]

Gretchenfrage
"Vanity is my favourite sin" Al Pacino (Devil's advocate) You will love this movie. You read my profile and decide for yourself about my generation. However as I have mentioned it before that armed only with FCOM developing procedures on FBW aircraft is asking for trouble. If experience on line differs from a procedure I agree you have to do something to salvage the situation but after that get in touch with the manufacturer. For all the experience on line you do not become a test pilot nor do you get any insight into the computer logics. You may have noticed many things suggested on PPRUNE vary from highly professional to downright dangerous. None of them can replace SOPs.

[Gretchenfrage]

vilas

Well, if you throw a stone at a herd of sheep, it's the one who gets hit that yells ....

On another note: I don't quite get you:

One one hand you say ...

However as I have mentioned it before that armed only with FCOM developing procedures on FBW aircraft is asking for trouble

... on what i could agree with you, only to hear you state ...

You may have noticed many things suggested on PPRUNE vary from highly professional to downright dangerous. None of them can replace SOPs

... which puts you right back to the pilots i fear, citing solely FCOM, QRH and ABNs, as in your post below.

Now what is it?

You can recite whatever you want, i will stand firm that on a high speed excursion at high altitude the chances that you will expose an aircraft to a dangerous situation are very much slimmer than falling into a very much more dangerous low speed situation when extending speed-brakes.

Once more: The last decades saw no aircraft crash due to high speed at altitude, but several crashed due to high altitude stalls.

Your choice where common sense lies.

[RAT 5]

But we have to realise that we are of a dying species, the one with experience and some common sense left. We are overwhelmed by the new generation who religiously follow the magenta line, the FCOM and SOPS without filter or questions.
Remember the former UAS by Airbus, that was amended after some incidents? It shows that not everything straight from the A/B horse's mouthes is incontestable and of final wisdom.

Slight thread creep, but I have to admit I always taught Boeing incipient stall recovery from stick shaker was, 1st elevator then a split second later add thrust. Guess what it is now. Aerodynamics on a basic aeroplane had never changed. I did, also, demo a stick shaker recovery from low level flight with A/P engaged by just adding power. It was always interesting, so they saw both sides of the coin. It wasn't going to work at medium levels or above, but….
Sadly, now, the syllabus I have to use does not include time for such demos. The knowledge transfer is much less than it was. Time is too squeezed.

[vilas]

Gretchenfrage
All I am saying is involve the manufacturer. They are in touch with operators across the world and are aware of incidents that happen. They have all the resources. You cannot device something on your own. If there is a problem they are answerable. You cannot replace a procedure listening to someone.

[IcePack]

Spool up time well yes takes a bit. Airbus speedbrake retract time with A/p engaged takes an age. Airbuses o/speed technique seems a little optimistic. :eek:

[vilas]

Gretchenfrage
The reason I keep saying involve the manufacturer is because of FBW. A conventional response to an under or over speed may not take into account the aircraft behaviour due normal law protections. There have been incidents of AP disconnection due over speed and then subsequent engagement of alpha prot causing rapid climb resulting in near air miss. There have been low airspeed events without any failure but due to unusual environmental changes. We know that a pilot cannot expect survive by his own experiences alone. The manufacturer with his resources provides a better platform to tackle these events. Experience is not a name given to mistakes we committed and got away.

[Gretchenfrage]

vilas

Don’t get me wrong; I sure enough don’t dare excluding any manufacturer. With the complex aircraft we fly, as a pilot it would be preposterous to think we simply know better.

Experience however should keep us alert. FBW is not the wonderful saviour the industry likes us to believe. There are still traps involved and, worse, reluctance to correct them due to some engineer’s pride, but mostly due to the deplorable pack of wolves called litigation lawyers especially from the USA. Any change, even of the most obvious design flaw, would have them backtrack any former incident involving the design, ensuing an avalanche of lawsuits.

The thread starts with the question of thrust reduction in case of overspeed:
Is it ok to go to idle, or should we follow the manufacturer’s advice to only go halfway and use speedbrakes.
Some say follow strictly manufacturer’s FCOM/QRH/SOP, others are quite reluctant to extend any speedbrakes.

We can debate for hours, but here’s the problem:
1. Aerodynamically it makes basically no sense at high altitude to destroy something we are normally struggling for, namely lift.
2. Overspeed at high altitude has not caused an accident in recent times, low speed (or low lift) has.

So why would any manufacturer want lift destruction to counteract high speed??

One of them because his FBW would climb in case of massive overspeed and I hope we all agree that this is undesirable. Another one because he wants thrust levers only halfway back due to its engines unusual long spool-up time.

In both cases I raise the ominous “Gretchenfrage”, the core question:
Why does the manufacturor not cure the sickness and simply fights the symptom? I say:

Get the FBW or EEC logic right before you suggest manoevers that put us in a worse situation to counteract the flaw!

That is what I mean by not unconditionally trusting manufacturers, FCOM/QRH and SOPs. They have an agenda that is called profit. I have one that is called survival, in the economical and physical sense.
They do not always match!

[Gysbreght]

Aerodynamically it makes basically no sense at high altitude to destroy something we are normally struggling for, namely lift.
(...)

So why would any manufacturer want lift destruction to counteract high speed??

One of them because his FBW would climb in case of massive overspeed and I hope we all agree that this is undesirable.Aerodynamically speedbrake extension creates drag to slow down the airplane. There is no lift destruction. Lift is maintained otherwise the airplane would start descending. Speedbrake extension reduces the maximum lift capability, but that is irrelevant because, firstly, the airplane is far removed from the maximum lift capability in an overspeed situation and, secondly, if the airplane slowed down to near its minimum speed it encounters buffet well before reaching the maximum lift capability, which is immediately restored upon retraction of the speedbrakes.

AFAIK the recommendation to use speed brake has no relation to the functioning of the overspeed protection feature.

Another one because he wants thrust levers only halfway back due to its engines unusual long spool-up time.

(...)
Why does the manufacturor not cure the sickness and simply fights the symptom? I say:

Get the FBW or EEC logic right before you suggest manoevers that put us in a worse situation to counteract the flaw!I don't know the reason for the long spool-up time at high altitude, but I think it is more likely to be the engine's surge margins than a 'flaw' in the FBW or EEC logic.

[OSCAR YANKEE]

@vilas

The manufacturer has to cover liabilities, and keeps that in mind when writing procedures.
Certain things they just drag their heels on. Denying issues at first, and then when presented with irrefutable facts, just say "this will be sorted in a future release".
We have had issues that took years for them to sort, still one outstanding A/THR issue thats been known for 5 yrs plus that they just get on to.......

[Gretchenfrage]

Gysbreght

Aerodynamically speedbrake extension creates drag to slow down the airplane. There is no lift destruction

I sincerely hope you are not a commercial pilot transporting SLF in "thin air"!
At least your statement made me stop reading your contribution any further .....

[Gysbreght]

Gretchenfrage,

no need to get personal ...

[vilas]

Gretchenfrage @OSCAR YANKEE
Since you went back to the original thread if you read the posts you will realise that those are not all from Airbus pilots. It is a mix bag neither all are of them are from their own experience either. Somebody says good idea somebody say bad idea another says it's settled. I quoted A320 official document and before it went in there Airbus gave elaborate presentation about the issue. I don't think anybody carefully read what it say. It just says to leave everything as it is and select lower speed. This what busav8r, Oscar Yankee said and you support it and yet you disagree because Airbus procedure says same thing. Your opposition is perhaps to use of speed brake. That comes when things have gotten worse and recovery procedure is required. We are faceless entities can say anything to each other doesn't prove a thing so don't so condescendingly include yourself in a threatened specie no grant would be forthcoming for your conservation.

[Gretchenfrage]

Since you went back to the original thread if you read the posts you will realise that those are not all from Airbus pilots. It is a mix bag neither all are of them are from their own experience either. Somebody says good idea somebody say bad idea another says it's settled. I quoted A320 official document and before it went in there Airbus gave elaborate presentation about the issue. I don't think anybody carefully read what it say. It just says to leave everything as it is and select lower speed. This what busav8r, Oscar Yankee said and you support it and yet you disagree because Airbus procedure says same thing. Your opposition is perhaps to use of speed brake. That comes when things have gotten worse and recovery procedure is required. We are faceless entities can say anything to each other doesn't prove a thing so don't so condescendingly include yourself in a threatened specie no grant would be forthcoming for your conservation.

no need to get personal ...

Gysbreght
I might have gotten a little personal if i read complete nonsense, sorry for that, but it is after all a pp forum..
Pretending that speedbrakes do not destroy lift is such nonsense. Why on earth would the red/black tape jump up when you deploy them, if not for loss of lift and by the way, we call these devices spoiler as well. They spoil what exactly?

vilas
Condescending or not, its the recipient who decides. Anyway, it is by far not only an Airbus matter, some experienced contributors here include Boeing as well, as their speedbrake logic is not beyond doubt, especially for such manoevers we discuss. But keep on adopting everything that is in the books, that makes you just the same faceless entity and no grant would be forthcoming for anyone who religiously follows sop into an incident, believe me.

Never stop expecting the unexpected :ok:

[OSCAR YANKEE]

@vilas - have a look at this one:


Incident: Jetstar A320 enroute on Mar 12th 2014, alpha floor activation (http://avherald.com/h?article=47196b94&opt=0)

;)

[vilas]

OSKAR YANKEE
Thanks for the article. The action of the pilot in this are in between what you said in post 91 and mine 46 and 51.You wanted to just observe till things sort themselves out and AB procedure said keeping AP and ATHR on just reduce speed and speed brakes as required. He did this but it was his judgment at that point that it wasn't working and he disconnected all automation and that complicated it further. I cannot question his judgment but I think having followed the recommended procedure he could have waited to see the results before disconnecting the AP because it appears that the speed trend and not actual speed triggered further actions. But if selecting lower speed and speed brakes were not enough then doing absolutely nothing and leaving things as they are may have been worse.

[OSCAR YANKEE]

The only thing to do in this scenario (high rate of climb at high alt, and increasing speed) -which an experienced airbus pilot will tell you - is to press VS0, and select a lower speed eg. .76.
This will arrest the climb and level off the A/C. (You might have to press VS0 a few times, if the a/c is already in ALT* (or ALT aquire in Boeing lingo.)

Then when the a/c has regained its composure you select V/S climb with a low rate eg. 500 fpm and monitor it closely as it creeps up to level.
(The rate of course depends of the weight and thrust rating of the A/C).

This way you avoid the drama of a high workload situation involving speed brakes, closure of thrust levers etc.

As a note. These comments are not intended to put down the individual involved in the situation.
He/she found himself in an unfamiliar situation that developed rapidly, and tried to cope as best as possible.
The rest of us can take note and learn....

[vilas]

OSCAR
Let's examine your suggestion. The aircraft was in ALTCRZ in which it is linked to Altitude in Alt window and when disturbed from it will try to get back to it by climbing or descending while VS0 is not linked to any altitude but V/S zero. If disturbed by updraft as was the case AC will deviate and try to maintain VS0 where ever it stabilises. So it is less aggressive. But in the present situation when the ALT mode is unable to prevent climb or descend changing to VS mode will cause larger deviations. Yes it may give you better ride because it accepts deviations. I don't see any magic solution in VS0. The pilot applied the correct procedure but may be he could have left the AP on till it disconnected on its own. It may have handled it better but not VS0.

[Goldenrivett]

Villas
The aircraft was in ALTCRZ in which it is linked to Altitude in Alt window and when disturbed from it will try to get back to it by climbing or descending while VS0 is not linked to any altitude but V/S zero.

If you read the article, the aircraft was in OPEN CLIMB.
"The aircraft climbed through FL373 when the first officer noticed the speed had increased to 0.81 mach and had engaged in a 3000 fpm climb, the speed trend indicator suggesting the aircraft would accelerate beyond the maximum mach number operating (MMO) of 0.82 mach."

In open climb, the aircraft attempts to maintain speed by adjusting pitch to change the V/S. 3,000 fpm with only 700 feet to go is excessive. Pushing V/S zero will change the auto thrust to speed control. Once the aircraft is under control again, a gentle climb rate of say 500 fpm using V/S would be sensible.

Why do you not like using V/S 0?

[framer]

My Lord I'm glad I don't fly an airbus, I don't understand half of what you guys just said. ( I've always been a bit slow though).

[vilas]

Goldenrivett
The initial part of the news seemed to suggest aircraft was at ALT. However you are right the AC was in OP CLB. My comments were for ALT mode. I don't have anything against VS0 mode rather in RVSM I thought everybody uses it in last few thousand feet to reduce ROC to avoid nuisance TA/RA. Just to recap the event the AC was climbing through FL373 to FL380 when he noticed the speed .81M and ROC 3000 and went to select Mach of .76. It is not clear if ALT* was engaged. If it was not the ROC would further increase to bring the speed back. Anyway with only 700 feet to go the SPEED ALT* should have engaged. At this point he disconnected the ATHR by bringing it to idle and also applied speed brakes. So by now he had done everything that should have been done. By selecting VS0 nothing more would have been achieved because the thrust was idle and FG in ALT capture mode. If the AP was kept engaged the problem should have settled. The workload increase was due to AP disconnection. If speed brake was in full position with AP ON the disconnection of the AP could cause the speed brakes to extend full from half. This would increase the VLS and the drag leading to alpha floor.

[OSCAR YANKEE]

@vilas.

You're not paying attention mate.

Does not matter whether a/c was in ALT* or not, by hitting VS0, you "break" the ALT* mode.
(Hence my comment "that you might have to press VS0 a few times because it will inevitably go into ALT* again with 3000ft/min ROC and 700' to go.)

No need for speed brake, or A/THR disconnection, if you just go VS0 and select speed .76. :ok:

And as for the comments of reducing ROC before level off, it is only rarely necessary above FL350,
and I think you will struggle to find any operator recommending the routine use of V/S mode at those levels irrespective of aircraft type....

[rudderrudderrat]

Hi OSCAR YANKEE
I think you will struggle to find any operator recommending the routine use of V/S mode at those levels irrespective of aircraft type....


SKYbrary - Rate of climb within last 1000 ft before cleared level (http://www.skybrary.aero/index.php/Rate_of_climb_within_last_1000_ft_before_cleared_level)
"many operators have standard operating procedures requiring the pilots to reduce rate of climb/descent to less than 1500 ft/min when in RVSM airspace or within the last 1000 ft before cleared level;"

You'll be one of those giving me the heart attack as I wonder if you'll ever level off approaching me! The automatics always do stupid things - they can't think, so please reduce your rate of closure.

[vilas]

OSCAR YANKEE
Oscar I am paying full attention. ALT* surely matters because ATHR would go to speed mode and in this situation it should go idle. He had already selected .76M and without ALT* that would have only increased the ROC to reduce speed. Coming to your point why do you want VS0 is to get ATHR in speed mode to bring the speed back and stop climb but when the guy has brought the thrust to idle with speed brakes and still the aircraft tends to over speed how VS0 would have helped? However had he left the AP on aircraft should have levelled out and he would have had more time to pay attention to adjust thrust manually or put it in auto. He followed the correct procedure except that there was no need to disconnect AP because had the over speed continued the AP would have tripped by HSP activation and then in any case you take over manually but at least give it a chance.

[OSCAR YANKEE]

You'll be one of those giving me the heart attack as I wonder if you'll ever level off approaching me! The automatics always do stupid things - they can't think, so please reduce your rate of closure.

Maybe im not explicit enough......
I wrote:

And as for the comments of reducing ROC before level off, it is only rarely necessary above FL350,
and I think you will struggle to find any operator recommending the routine use of V/S mode at those levels irrespective of aircraft type....

I know the recommendation as well as anyone, but tell me the last time you had to intervene to reduce the ROC above FL350 ??

Maybe the A/C I have flown have been underpowered, I dont know.......

As the example above - high ROC above FL350, will "normally" only happen in empty A/C or if you get a WS type scenario.


@Vilas.

All im trying to say is no A/C can defy the laws of physics, no matter how advanced the A/P. Sometimes it needs a bit of help.....

And as I said in my first post.
I have had the good fortune of reading quite a few safety reports (incl. FDR read outs) similar to the one above from Avherald - and my personal opinion remains - you are better off leaving the A/THR + A/P in and take a minor overspeed, than ending up in the mess as described above.

Follow the official procedure, and you might end up one day with the "Successfull operation - but the patient died"-scenario......

[bugged on the right]

Just found this thread and it has given me a great deal of merriment. As a former Flight Engineer and full time cruise autothrottle on the Tristar, when the speed went up unexpectedly, I would pull the no2 throttle lever back an inch and wait. It was busy work on the way to Japan some days but I never had a high speed or low speed warning. All smooth with no checklists, speed brakes, recall items or need for the PF to pitch up. Looks like the modern ones are hard to handle despite the automation.

[busav8r]

I've been away from this forum for quite a while and for my surprise I found out this thread is still "alive".

Like I said in a post before, the most sensible approach for an overspeed recovery on the A320 is... doing nothing! Simply sit and wait and monitor if the ATHR is doing its job. Don't touch the AP and most particularly don't use the freaking SB at very high levels.

KISS.