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A320 procedures

Discussion in 'Technical Talk' started by seagull, Apr 30, 2017.

  1. seagull

    seagull Well-Known Member

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    On the Asiana accident the captain was coming off the A320 and was still on his initial operating experience with a brand new check airman in the right seat. They were cleared for a visual approach with a LOC backup. They were quite high and clearly concerned about that. They were at 1500' or so and had set the MAP altitude (3000') in the window and apparently had pushed the FLCH, with the speed selected to 137kts (Vapp). He then turned the a/p off. With the power advancing to THR REF the PF then retarded the throttles manually and it went into "hold" mode.

    My question is what would happen on the Airbus with the same sequence of button pushes? Is there anything similar to the "hold" mode where it lacks all protections and will let you stall the airplane?
     
  2. Der_Meister

    Der_Meister Well-Known Member

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    Stall no, low airspeed possibly depending on what all you did. The auto thrust in the AB is a bit different from the Boeing products.

    having flown both I can't really say I prefer one over the other, they are just different. You live and Die by your FMA's!!!!
     
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  3. Zapphod Beblebrox

    Zapphod Beblebrox Well-Known Member

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    Essentially and probably the same thing. I say probably because I don't know, and haven't reviewed the technical details of the Asiana accident. On the Bus the names and modes are different but the results are similar. The equivalent of FLCH, flight level change, on the Bus is Open Descent or Open Climb, "OPEN CLB", "OPEN DESC." There is no separate button, you pull the altitude set knob to engage the open mode.

    If some form of descent is already annunciated, like rate descent, then going open simply asks the auto-thrust to go to idle and the speed could either be managed, MCDU computed approach speed, or other, or pilot selected. The problem is that there will be no vertical event to get the mode to change, except for contact with the ground. If the FCU altitude is set above you, as it was with Asiana, then there will be no intercept, except for ground contact. There is no Glide Slope capture to force the FD/AP and system back into approach speed mode, so the aircraft will simply sit there at idle on speed until it hits the ground.

    At AA in the limitations section of VOL 1 OM 1.10.1 - Open Descent - The use of Open Descent, "OPEN DES", is prohibited inside the FAF, or below 1000 feet AGL during a visual approach. (A)

    Additionally, you can recover the use of speed mode by simply turning off BOTH flight directors. One of the idiosyncrasies of the Airbus is that if there is flight director guidance on either side and you are in open climb or descent they will stay that way as long as at least one FD is on. You must turn off both or the MCDU will direct the selected mode to the working FD side. Flying a bus in with one FD on and the opposite on off will not go well. The logic of the airplane is to seek MCDU / FCU guidance when it can. When there is no guidance, the system defaults to speed mode and the thrust levers will simply move to hold speed. You push down the thrust goes towards idle, you pull back, thrust increases to hold speed. This is the only acceptable mode during a visual approach.

    If there is no glideslope, either ILS or RNAV generated, on a visual approach; turn the magic off, or it will try to kill ya.
     
  4. seagull

    seagull Well-Known Member

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    The Boeing is similar in many respects. What I am really trying to get at is if it is possible that the Captain on Asiana, doing the above, was somehow reverting to an Airbus procedure from his previous 10 years.

    Definitely agree with the live and die by the FMA's, and I have been somewhat familiar with AI bit this is helpful, the more the better, so elaborate as much as you want!
     
  5. Der_Meister

    Der_Meister Well-Known Member

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    well not seeing the thrust levers move is normal in the AB. If they are not moving in the Boeing either they are off or you at throttle hold. I would consider that to be a factor
     
  6. seagull

    seagull Well-Known Member

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    I definitely agree with you on that. I am wondering about the Captain pushing FLCH, but I think he just was not sure and was concerned about being high.
     
  7. Der_Meister

    Der_Meister Well-Known Member

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    bad procedure usage of FLCH
     
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  8. Cherokee_Cruiser

    Cherokee_Cruiser Well-Known Member

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    Setting the higher altitude while you are lower and pulling altitude knob (equivalent of FLCH) will get "THR CLB" in the A/T column (thrust climb) and "OP CLMB" (vertical), in this case, just like FLCH climb without regards to constraints. So the A320 would have done the same thing as the 777 did. The Asiana CA corrected it by pitching the nose down (AP off) and manually bringing back the thrust levers to idle, which put it into "hold" mode.

    On the A320, manually bringing the thrust levers all the way to idle will turn the autothrust off. And the power will be at idle. With the autothrust off, there is no "hold" indication. Speed column will be blank on the FMA. On the A320 once you've manually taken the power to idle, it won't come back alive by itself unless it enters alpha floor protection which adds toga thrust. The pilot is responsible for adding his own power at that point with the thrust levers.

    Even with autothrust off, protections are available and the airplane can add TOGA thrust. Where the protections come in do depend on AGL. Above 100 ft AGL/RA, the crew can (once slow enough, with a high AOA) get into alpha protection and then alpha max at which point you'll get alpha floor and toga lock (full power comes in even with thrust levers staying at idle). Like the Boeings 'beep-beep-beep-beep' the A320 has an aural "Speed speed speed" , so like the Boeing, that aural warning would have come first. In this accident it seems at 100 ft AGL is when they got the low speed warning when they were at 112 knots.
     
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  9. seagull

    seagull Well-Known Member

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    Thank you, that is what I thought. The real difference is that alpha-floor would have kicked in on the Airbus in this scenario as it was prior to 100'.
     
  10. Derg

    Derg Naval Intelligence, MCRN Staff Member

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    Nope. Except in "alternate law" which requires turning off a couple ADRs or some other cascading failures.

    Or pissing off the HAL 9000 when he doesn't think you'll complete the mission.
     
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  11. Autothrust Blue

    Autothrust Blue "This is a God damn waste of time!"

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    ...well, on the 175...

    @jtrain609
     
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  12. Derg

    Derg Naval Intelligence, MCRN Staff Member

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    Ha! :)
     
  13. jtrain609

    jtrain609 I'm a carnal, organic anagram.

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    FIFY.
     

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