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Thread: Runway Incursion at Shanghai Hongqiao Airport

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    Member hongmng's Avatar
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    Default Runway Incursion at Shanghai Hongqiao Airport

    http://avherald.com/h?article=49f37b96&opt=2048

    Surprised no one brought this one up

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    Hmm... looks like in this case, pulling up relentlessly saved the day.
    Be alert! America needs more lerts.

    Eric Law

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by elaw View Post
    Hmm... looks like in this case, pulling up relentlessly saved the day.
    In an Airbus in normal law, pulling back relentlessly on the sidestick will not result in a relentless pull-up simply because HAL won't follow your commands.

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    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    In an Airbus in normal law, pulling back relentlessly on the sidestick will not result in a relentless pull-up simply because HAL won't follow your commands.
    It could result in momentarilly exceeding alpha max though. Protections reduce the chance of this but do not eliminate the possibility. For one thing, you are in direct law on the take-off roll until you enter flight mode, at which point alpha-protect is equal to alpha-max for the first five seconds. If you pull up agressively full aft stick while in ground mode at Vr you will first get the full 2G envelope limit in pitch (reduced from 2.5G because the flaps are out) before alpha protect limits elevator deflection in the air. In an emergency manuever I can see this leading to an AoA exceeding stall at least momentarilly. The two critical bits of caveat you will find in the FCOM are 'sidestick moved gently to full aft' and 'reduced possibility of exceeding'. FBW protections control elevator deflection, not physical momentum. I wouldn't put blind faith in it, but then again, there's no procedure for leaping over crossing traffic on takeoff and it's probably best to momentarilly exceed alpha max at that point anyway. I would also get the gear up directly after liftoff.

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    It could result in momentarilly exceeding alpha max though. Protections reduce the chance of this but do not eliminate the possibility. For one thing, you are in direct law on the take-off roll until you enter flight mode, at which point alpha-protect is equal to alpha-max for the first five seconds. If you pull up agressively full aft stick while in ground mode at Vr you will first get the full 2G envelope limit in pitch (reduced from 2.5G because the flaps are out) before alpha protect limits elevator deflection in the air. In an emergency manuever I can see this leading to an AoA exceeding stall at least momentarilly. The two critical bits of caveat you will find in the FCOM are 'sidestick moved gently to full aft' and 'reduced possibility of exceeding'. FBW protections control elevator deflection, not physical momentum. I wouldn't put blind faith in it, but then again, there's no procedure for leaping over crossing traffic on takeoff and it's probably best to momentarilly exceed alpha max at that point anyway. I would also get the gear up directly after liftoff.
    But doesn't the logic include a tail-strike protection too? If so, because in the A320 the tail strike happens before stall, the airplane will lift off first and then alpha prot will kick in without ever stalling.

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    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    But doesn't the logic include a tail-strike protection too? If so, because in the A320 the tail strike happens before stall, the airplane will lift off first and then alpha prot will kick in without ever stalling.
    Where did you read that? No, you can freely drag the tail to your heart's content. That's how they calculate Vmu during certification. The rest of your post I don't follow.

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    Where did you read that? No, you can freely drag the tail to your heart's content. That's how they calculate Vmu during certification. The rest of your post I don't follow.
    Hmmm.... I wonder how Airbus determines the stall speed during certification. They can't because the normal law won't allow them to stall.

    I am not saying that there is a tail strike protection. I seem to remember having read about it somewhere, but I can be wrong.
    Now, your Vmu certification argument is ridiculous.

    The rest of my post... What happens if you pull up hard a bit below Vr in an A320?
    If the tail strike protection exists, then the pitch will be limited first by the tail strike protection, then the plane will become airborne, the plane enters flight mode, alpha-protect is equal to alpha-max for the first five seconds (which is less than Alpha critical/stall) and the plane doesn't stall.
    If the tail strike protection doesn't exist, then you have first a tail strike (which happens at less than the critical AoA), then the plane becomes airborne, the plane enters flight mode, alpha-protect is equal to alpha-max for the first five seconds (which is less than Alpha critical/stall) and the plane doesn't stall (which, in any event, is jot what happened since there was no tail strike).

    And did you note that I was replying to a humorous comment?
    Hmm... looks like in this case, pulling up relentlessly saved the day.


    The answer to this could be:
    - They didn't pull up relentlessly because if they had there had been a tail strike (which didn't exist)... or...
    - That's ok in the A320; you can pull up relentlessly because HAL will take care of tail strikes and stalls.

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    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    Hmmm.... I wonder how Airbus determines the stall speed during certification. They can't because the normal law won't allow them to stall.

    I am not saying that there is a tail strike protection. I seem to remember having read about it somewhere, but I can be wrong.
    Now, your Vmu certification argument is ridiculous.

    The rest of my post... What happens if you pull up hard a bit below Vr in an A320?
    If the tail strike protection exists, then the pitch will be limited first by the tail strike protection, then the plane will become airborne, the plane enters flight mode, alpha-protect is equal to alpha-max for the first five seconds (which is less than Alpha critical/stall) and the plane doesn't stall.
    If the tail strike protection doesn't exist, then you have first a tail strike (which happens at less than the critical AoA), then the plane becomes airborne, the plane enters flight mode, alpha-protect is equal to alpha-max for the first five seconds (which is less than Alpha critical/stall) and the plane doesn't stall (which, in any event, is jot what happened since there was no tail strike).

    And did you note that I was replying to a humorous comment?
    Hmm... looks like in this case, pulling up relentlessly saved the day.


    The answer to this could be:
    - They didn't pull up relentlessly because if they had there had been a tail strike (which didn't exist)... or...
    - That's ok in the A320; you can pull up relentlessly because HAL will take care of tail strikes and stalls.

    I see your point. Around Vmu, in direct law, the tail and the runway are likely to be your alpha protection on a geometrically-limited aircraft. There was no mention of a tail strike here and the rotation was initiated at 130kts, which is the low side of Vmu for the aircraft. So I assume that they didn't just pull up relentlessly.

    But the thing I was pointing out is that momentum is going to possibly win over alpha protect, at least momentarilly, if you pull full aft too abruptly once you are flying. You are commanding alpha max with those underslung engines at TOGA. I bet you can make it past CL max, lose precious height, maybe drop a wing into somebody else's fin... It's not always OK to trust HAL and just yank the stick back. I hope pilots understand that. Again, all the AB lit says "gently".

    And no, the A320 isn't protected by logic from tail strike. I think the longer A340's have some form of protection in the form of a PFD indication (Maybe I'm wrong about that one). The B777 offers it though. In that case the PFC's are limiting elevator without giving feedback to the control columns (talk about HAL!) It would seem very unsafe to me to actually limit pitch below tailstrike at that critical point. Isn't the whole idea of minimum unstick speed to accommodate emergency situations like this? Better to strike the tail on the runway than on somebody else's business class section, eh?

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    Isn't the whole idea of minimum unstick speed to accommodate emergency situations like this?
    Hmmm, no. Sorry.

    Vmu (minimum unstick) is the minimum speed at which the plane can possibly lift off the ground and continue the take-off. It is one of the many "engineering speed" (not available to the pilot) used to determine other "pilot speeds" (the ones in the manuals).

    In particular, it establishes a lower bound for Vr. Vr must be such that, if the rotation is started exactly at Vr at the maximum practicable pitch rate (i.e. relentless pull up), the plane will lift off the runway at a speed that is not less than a prescribed factor above Vmu (the factor varies between 1.04 and 1.10 depending on whether you are in the "all engines operative" or "critical engine inop" whether the Vmu attitude is limited by the geometry of the plane or not).

    So a relentless pull up at Vr may lead to a tail strike and/or a stall but nor before the plane lifted off.

    In short, you need to demonstrate the minimum safe lift-off speed first, and then demonstrate that actual lift off will happen with at least a prescribed margin above that minimum safe speed.

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    The A320 family offers no tailstrike protection as such. Rather, the airplane starts screaming "PITCH! PITCH! PITCH!" when approaching limits, which vary by model. The system monitors both the actual pitch angle and the rate of change thereof. As a result, it's somewhat jumpy. Both times I've had it activate, there was no problem either with pitch itself or the rate of change. In fact, both times were on landing, one of them long AFTER touchdown, when the airplane was pitching DOWN.

    Computers, I tell ya...

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    Senior Member LH-B744's Avatar
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    Quote Originally Posted by ATLcrew View Post
    [...]

    Computers, I tell ya...
    Yes. What are they good for, if not saving lifes! Let me againg quote this flight:
    Two German pilots failed during an A320 flight.

    Probably, the CEO of my favourite airline is tired to read comments about another A320 flight. And since he published where he began in the LH company, he gains 110% of my respect (of before 100%). Captain Spohr knows how to use that a/c.

    So, what went wrong during G1 flight 888T?

    Since I have watched flight G1 888T on TV, I doubt that computers are able to make flights safer. Or, as my father (*1945) would've said,
    a computer can't be more intelligent than the person who sits infront of it!

    PS: If a computer tells me how to fly, I don't trust this computer.

    Even the point in time when the flight computer in an Airbus says, no, I don't like to continue the flight,
    is not fix!

    I've never understood why young aviation enthusiasts prefer Airbus. Although they don't know how to handle a 100% computerized aircraft like an Airbus, if the Airbus flight computer says:
    oha. this is too difficult. all flight computers are switched off!

    When is an airbus still a safe aircraft? ONLY, when there are men who are able to spontaneously take over when the Airbus flight computer exits.
    LH also has a intercontinental history, the Hamburg - Düsseldorf - Shannon - NYC route, open since June 1st, 1955.
    A/C type: Lockheed Super Constellation.
    The airline code since a few weeks is no longer LH, but the operator stays the same on the DUS - NYC route ...

    Aviation enthusiast since more than 30 years. A whole decade here on this platform.

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    Senior Member LH-B744's Avatar
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    Computers who try to set up laws. Is this Terminator Part III?

    Damn, I thought I'd know how to use computers since ... 1985. Fortunately, the movie ended with the reign of

    the humans!

    Btw, #777 must be a good number.

    PS: And Dredd (2012) is a good movie. Not all FSK 18 movies are bad due to a lack of a story...
    Computers have ALWAYS tended to be misused. Not only since that movie: 'This is the doorman computer of block # 297846. No human being is able to enter that block during the next 72 hours due to technical difficulties.'

    This is what we all want.
    Last edited by LH-B744; 10-22-2016 at 04:07 AM. Reason: Computer failure.
    LH also has a intercontinental history, the Hamburg - Düsseldorf - Shannon - NYC route, open since June 1st, 1955.
    A/C type: Lockheed Super Constellation.
    The airline code since a few weeks is no longer LH, but the operator stays the same on the DUS - NYC route ...

    Aviation enthusiast since more than 30 years. A whole decade here on this platform.

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    Senior Member LH-B744's Avatar
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    Quote Originally Posted by hongmng View Post
    http://avherald.com/h?article=49f37b96&opt=2048

    Surprised no one brought this one up
    Hi, hong. After all what I've said about Airbus laws, which should especially be used by Airbus pilots to avoid accidents, it seems like this happening ended without
    1 casualty
    and, more important, without
    1 fatality.

    This is why I joined this platform, and this is the reason why I like aviation. Not everybody is a hero like Captain Sullenberger. But
    we safe lifes if it comes hard.

    PS: Hongqiao is not (yet) a frequently used airport for major European airlines. Do you like to change that?
    Last edited by LH-B744; 10-22-2016 at 04:36 AM. Reason: Hongqiao?
    LH also has a intercontinental history, the Hamburg - Düsseldorf - Shannon - NYC route, open since June 1st, 1955.
    A/C type: Lockheed Super Constellation.
    The airline code since a few weeks is no longer LH, but the operator stays the same on the DUS - NYC route ...

    Aviation enthusiast since more than 30 years. A whole decade here on this platform.

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    Senior Member Evan's Avatar
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    Quote Originally Posted by LH-B744 View Post
    if the Airbus flight computer says: oha. this is too difficult. all flight computers are switched off!
    Every commercial aircraft operating in RVSM airspace is flown by a computer most of the time. It's called autopilot. And yes, if things get too difficult it switches off. That happens in an A320. That happens in a 737. That hapens in your beloved 747. FBW itself is just a means of translating pilot commands into flight surface movements and FBW has never failed due to computers switching off. Traditional cable-control has failed a number of times. So what will it take to earn your trust?

    It's almost funny how ignorant everyone on aviation forums are about FBW. They spout this kind of nonsense as if legions of aerospace engineers are just complete idiots. If you knew how much redundancy Airbus had to build into the A320 to get it certified, how paranoid the regulators were and how over three decades that redundancy has never been needed to it's full extent you might begin to understand how counter-productive all this scarebus chatter is.

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    Quote Originally Posted by Evan View Post

    It's almost funny how ignorant everyone on aviation forums are about FBW. They spout this kind of nonsense as if legions of aerospace engineers are just complete idiots. If you knew how much redundancy Airbus had to build into the A320 to get it certified, how paranoid the regulators were and how over three decades that redundancy has never been needed to it's full extent you might begin to understand how counter-productive all this scarebus chatter is.
    How easily we see ignorance in others...

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    Quote Originally Posted by Gabriel View Post
    In an Airbus in normal law, pulling back relentlessly on the sidestick will not result in a relentless pull-up simply because HAL won't follow your commands.
    Maybe I'm arguing over semantics, but I'm not sure it's correct to say "Hal won't follow your command", because it will give you the maximum available nose-up without stalling

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    Quote Originally Posted by Black Ram View Post
    Maybe I'm arguing over semantics, but I'm not sure it's correct to say "Hal won't follow your command", because it will give you the maximum available nose-up without stalling
    Maybe I'm arguing over details, but it won't do that either.

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    Quote Originally Posted by Black Ram View Post
    Maybe I'm arguing over semantics, but I'm not sure it's correct to say "Hal won't follow your command", because it will give you the maximum available nose-up without stalling
    Below certain speed threshold it will give you a load factor proportional to the stick displacement. 100% stick back will be 2.5G.
    Below that threshold, it will give you a pitch rate proportional to the stick displacement. At 100% stick back it will be... I don't remember... was it 5 deg per sec?
    In both cases, the AoA will be capped first by Alpha max, so if Alpha max is achieved before 2.5G or 5 deg per sec, it will not pitch up past Alpha max.
    Alpha max is less than Alpha stall.

    I am simplifying. There are changes in the behavior as you pass through Alpha floor and Alpha proc before reaching Alpha max.

    And during the take-off run, rotation and the very first seconds of climb, the behavior is also different, as explained by Evan.

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    Senior Member Gabriel's Avatar
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    Quote Originally Posted by Evan View Post
    FBW itself is just a means of translating pilot commands into flight surface movements... It's almost funny how ignorant everyone on aviation forums are about FBW. They spout this kind of nonsense as if legions of aerospace engineers are just complete idiots. If you knew how much redundancy Airbus had to build into the A320 to get it certified, how paranoid the regulators were and how over three decades that redundancy has never been needed to it's full extent you might begin to understand how counter-productive all this scarebus chatter is.
    For the record, I have nothing against FBW. I do have some objections to Airbus' approach to FBW, i.e the "transfer function" that "translates pilot commands into flight surface movements". Do I think it's unsafe? No. But I do like Boeing's approach better.

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    Senior Member Evan's Avatar
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    Quote Originally Posted by Gabriel View Post
    For the record, I have nothing against FBW. I do have some objections to Airbus' approach to FBW, i.e the "transfer function" that "translates pilot commands into flight surface movements". Do I think it's unsafe? No. But I do like Boeing's approach better.
    Boeing is also using c-star control law. What do you mean by "transfer function"?

    I probably prefer the yoke/column as a FBW traducer. The sidestick was a noble idea inspired by the space program but it really overestimated pilots not trained in a space program.

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