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?

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.

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.

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

"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)

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.

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.

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?

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.?

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:

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.

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

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.

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.

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/H...Considerations

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

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).

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

sonicbum
What happens to Idle factor in open descent?

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!

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

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.

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:

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.

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

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).

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

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

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

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.

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

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

uncomfortable
 

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:

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?

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.

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.

Hi Rat 5,
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.

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:

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?

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?

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:
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. :}

Cosmo
 

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:

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?

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!