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Flying into the yellow band (Min. Manouvering Speed)

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Flying into the yellow band (Min. Manouvering Speed)

Old 18th Dec 2021, 14:57
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Flying into the yellow band (Min. Manouvering Speed)

G'day

Just trying to clarify and gather some different views on a recent scenario: Was held high by ATC and when cleared resorted to FLCH and speed brake to get back to a more manageable path. During this, speed went slightly into the yellow band region, and I was advised to never ever do this again as this is 'forbidden'. On the other hand, other colleagues seem not to care about this, their view (and mine) is that being in a descend and the wing being unloaded, I could hardly get in a potential stall situation. Of course I have to keep an eye on the red band and control the speed brakes accordingly. Worth mentioning is that we were in a long straight segment, so no sharp turns were expected either.

Thanks!

BF
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Old 18th Dec 2021, 15:40
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I think it is normally avoided. I suppose the further into it you go, the higher the risk. I would avoid it in turbulent conditions and limit bank angles. Perhaps only when wings are level and in smooth conditions and then…..not too far into the amber band.

I don’t think that the wing is necessarily at less than 1g just because you are descending, so that doesn’t make sense.
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Old 18th Dec 2021, 18:01
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The same thing sometimes happens on the bus. I think some forget there’s quite a margin to the stall at the top of the yellow band. The plane won’t fall out of the sky. If the air is smooth and you’re descending, I don’t see anything inherently dangerous about being SLIGHTLY below it momentarily.
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Old 18th Dec 2021, 18:15
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There is no issue going into the lower amber band, however the basic 25° bank + 15° overshoot is not completely assured so you have to limit your bank angle.

Depending on the type of Boeing you will get different requirements, but on the classic non-fly-by-wires I believe you have to go into HDG SEL and limit the maximum bank angle. Halfway down the amber band, you should set 10° which gives you max 25° (10° with 15° overshoot taken into account).

It is fairly uncommon to get into the amber band during descent, it does happen in cruise if ATC needs you higher than optimal and starts playing with speed restrictions.

Last edited by BraceBrace; 18th Dec 2021 at 19:43.
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Old 18th Dec 2021, 20:54
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Airplane doesn't fall out of the sky 1 kt below the amber band, but then again, surely there has to be a better way of operating the aircraft - perhaps one that doesn't require reducing your stall margins beyond that what Boeing (or the airline, as it's configurable) thinks it's appropriate.

I'm a simple guy, I try to stay away from the amber and red stuff. It reduces the chances of visiting the chief pilot's office as well.
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Old 18th Dec 2021, 20:59
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Who said the amber band is forbidden? It means caution. If you're not turning there's no problem.

Ask them to show you where it's written...
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Old 18th Dec 2021, 21:20
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But if you are turning:-
Low speed awareness in many aircraft is computed from AoA, thus it will be adjusted for a turn.
If not then the alerting value should have some margin for bank angle included.

An amber alert - caution, is for aircrew awareness and subsequent response (CS / FAR 25)
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Old 18th Dec 2021, 23:28
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Not answering your question specifically, but the top end of the LSC is invariably not much below min drag speed. Once cleared to descend, if you are using speedbrake then a higher IAS will significantly increase the drag and hence steepen the descent somewhat.
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Old 19th Dec 2021, 00:45
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No, it's not going to fall out of the sky under those conditions. On the other hand, it's poor flying.

The reason for the amber bar is to keep you well away from falling out of the sky. Many regulators and small aircraft associations are beating their heads against a wall trying to reduce the rate of stall accidents, while as airline pilots we almost never see this kind of accident. The reason is that instead of flying the aircraft in a manner that prevents a stall, we fly in aircraft in a manner that prevents getting anywhere close to a stall. Hard to go further into the details since we don't know your aircraft type but for example on the Airbus 320 getting just 2 knots into the VLS during manual flight will remove the FD bars and if the autothrust is on engage speed mode to power out of the VLS. Not going to help you descend.\

Bottom line: If you make a mistake and end up in the amber bar, the plane is fine but it's still a mistake.
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Old 19th Dec 2021, 02:41
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Learn from your mistakes.
At my employer that would have been a “SPEED” call out before you even got to yellow.
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Old 19th Dec 2021, 03:02
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Learn from it.
At my employer that would have been a “SPEED” call out before you even got to yellow.
In any case (mostly) unnecessary.
Descending clean in FLCH, were you speed restricted by ATC? Why not increase the speed by 20-30kts for an increased descent then pull the spoilers?
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Old 19th Dec 2021, 11:03
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Originally Posted by B2N2 View Post
Learn from it.
At my employer that would have been a “SPEED” call out before you even got to yellow.
In any case (mostly) unnecessary.
Descending clean in FLCH, were you speed restricted by ATC? Why not increase the speed by 20-30kts for an increased descent then pull the spoilers?
Speed callouts have their place indeed and I have nothing against that, on the contrary, it improves awareness when this might happen "unexpected". But the question is: is it forbidden? It is totally not. All of this IS explained in Boeing manuals, so I don't understand the "forbidden" reaction of pilots.

It's funny to notice that ie for a B737, in case of engine failure on takeoff, nobody makes a problem of limiting the bank angle to 15° when flying 400ft above the ground. All this while the background idea is the exactly same: assuring you stay within a safe maneuver capability. Yet in cruise we're going to go callouts and state "that's not allowed"?

It is allowed by Boeing, as long as you limit bank angle appropriatly. I think understanding what is happening is much more important than bluntly calling out and creating an athmosphere in which somebody apparently did something wrong. Because he didn't really do that...

Last edited by BraceBrace; 19th Dec 2021 at 12:52.
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Old 19th Dec 2021, 16:20
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Originally Posted by B2N2 View Post
Learn from it.
At my employer that would have been a “SPEED” call out before you even got to yellow.
In any case (mostly) unnecessary.
Descending clean in FLCH, were you speed restricted by ATC? Why not increase the speed by 20-30kts for an increased descent then pull the spoilers?
One can always learn something from the others, in this case not to get into the yellow band with this particular colleague again

And we were indeed speed restricted by ATC, so increasing the speed was not available for us at the time, to make things worse we were slightly overweight for the approach (due to a flight planning mistake) and the idea was to descent in FLCH, with speed brakes and added power to burn the fuel (yes, ugly, I know).

Thanks for great answers so far,

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Old 19th Dec 2021, 16:27
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True, it’s not forbidden.
Its a caution zone however and not for “normal operations” and it at least appears to have been unnecessary under the described conditions.
Point being, anticipating is part of airmanship.
As soon as you notice ATC is ‘keeping you high’ formulate a plane how to fix it further down the line. Consider upcoming speed restrictions, ATC “expect” instructions ( expect this Arrival, expect direct in 15 miles, expect to follow) yadayadayada.
Like build the picture in your mind.
Ask the other pilot, hey any suggestions on how to fix this?
Then if you expect to be out of options soon as in ATC is putting us in a situation I can’t fix then request a descent or a delay vector.
I fly an absolute beast of an airplane and there are certain things we just can’t do with something the size of an ocean liner.
If you (ATC) insist we descend at 300+ kts then we’ll need half an average European country to slow down.
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Old 19th Dec 2021, 16:31
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Originally Posted by Broomstick Flier View Post
One can always learn something from the others, in this case not to get into the yellow band with this particular colleague again

And we were indeed speed restricted by ATC, so increasing the speed was not available for us at the time, to make things worse we were slightly overweight for the approach (due to a flight planning mistake) and the idea was to descent in FLCH, with speed brakes and added power to burn the fuel (yes, ugly, I know).

Thanks for great answers so far,
Ah well, sometimes it can’t be pretty and no matter what your plans and your best intentions it all goes out the window.

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Old 20th Dec 2021, 10:45
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BF,

May I ask the scenario, was FLCH being sluggish or did you select a speed in the amber band? Just curious.
I am also on the side that unloaded wings and not too far into the amber band is nothing anyone should throw a fit about.
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Old 22nd Dec 2021, 03:52
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I’m sorry, but this
their view (and mine) is that being in a descend and the wing being unloaded, I could hardly get in a potential stall situation
is complete nonsense. In any normal descent, the load factor will still be about 0.999. The wing is hardly unloaded.
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