A320 SIM SCENARIO
While cruising at 390 and max weight, Being given a 70 knot instant tailwind gain, simulating jet-stream crossing, airspeed drops to alpha prot autopilot drops off.
instructor is asking for thrust to be reduced to idle. what is the logic here? |
Stall recovery after encountering a mountain wave?
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Originally Posted by MD83FO
(Post 10835255)
While cruising at 390 and max weight, Being given a 70 knot instant tailwind gain, simulating jet-stream crossing, airspeed drops to alpha prot autopilot drops off.
instructor is asking for thrust to be reduced to idle. what is the logic here? Reference (Airbus) is in FCTM -> Abnormal and emergencies procedures -> MISC -> Upset prevention and recovery. Your operator will probably have something tailored. |
Originally Posted by MD83FO
(Post 10835255)
While cruising at 390 and max weight, Being given a 70 knot instant tailwind gain, simulating jet-stream crossing, airspeed drops to alpha prot autopilot drops off.
instructor is asking for thrust to be reduced to idle. what is the logic here? |
Originally Posted by vilas
(Post 10835396)
The recovery is to push the nose down to reduce the AoA. But with the tail wind as the speed drops and ATHR will drive the thrust to Max cruise thrust. That may cause a pitch up preventing nose down movement. In that case close thrust and push the nose down.
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Originally Posted by vilas
(Post 10835396)
The recovery is to push the nose down to reduce the AoA. But with the tail wind as the speed drops and ATHR will drive the thrust to Max cruise thrust. That may cause a pitch up preventing nose down movement. In that case close thrust and push the nose down.
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Originally Posted by TheBat
(Post 10835471)
vilas, every post that I have seen from you is always to the point and spot-on. I feel the need to say: Bravo!!!
I would also like to say thank you to vilas 🙏 |
The SOP of THR LVRs to idle was not mentioned at the Vienna Airbus safety conference that analysed the speed decay in high altitude cruise scenario. There was another one 8 years ago. Both over the same airspace (Iran) interestingly, suggesting local effects.
With speed decay at high weight max altitude, it is likely that as near as maximum thrust is set anyway. There will likely be no further pitch up moments from increased thrust as there won't be much. The most important thing with speed decay in cruise below GD is to descend. Point the nose down to gain speed and decrease the AoA and turn offroute/Mayday as required. Sure, IF the nose does not come down, THEN reduce the thrust but that's full UA territory, and questionable whether the OP's sim has that fidelity. Refer FCTM>PR>NP>SOP>150>Speed Decay during cruise. "If the aircraft speed goes below GD with max thrust available in use, ... descend." For those who have access - Airbus world - Safety Conferences>2018>Day 1>Climb and Cruise events. P28 "If airspeed reduces below GreenDot with the maximum available thrust in use, the only way to avoid the risk of increasing the angle of attack is to descend" Alpha prot or not, pointing the nose down to reduce the AoA is the most important thing. Yes, reducing thrust may help that in an extreme upset, but it's not the standard SOP every speed decay and I would argue that there's negative training going on in the OP's situation. |
At high alt the thrust is within 2-4 % N1 of max available, so any increase would have a negligible pitch effect if any at all.
Teaching students to close the trust is negative training, self-made procedure. The instructor should either explain what specific trick is he trying to teach and carefully insist the students understand its limited scope, or stick to the book script. A general comment, all devout followers please note that vilas argues to close the thrust specifically in the presence of such an engine pitch-up moment that a nose down movement cannot be achieved. |
While cruising at 390 and max weight, Being given a 70 knot instant tailwind gain, simulating jet-stream crossing, airspeed drops to alpha prot autopilot drops off. Screwing around with thrust levers adds another variable to the picture which you don't need. Only then can you make the decision to descend, and the appropriate way to do it (ie get out of alpha protection then use VS etc). |
Screwing around with thrust levers adds another variable to the picture which you don't need. |
The first thing you should be doing is nothing (IMHO, of course), provided that the aircraft is still in normal law. The flight control law will apply full down elevator if necessary to protect the AoA. |
Originally Posted by vilas
(Post 10835931)
Not true! Alpha prot is latching condition. Once alpha prot is activated if you do nothing it will maintain alpha prot by doing what ever it takes yes even climbing. In the airprox incident between A330 and A340 over the Atlantic same think happened pilot disconnected the AP but didn't break the alpha lock by pushing on the stick. The aircraft trying to maintain the alpha lock zoomed up past incoming A340. To accelerate past Alpha lock it needs to be broken by pushing forward.
If the AoA continues to increase (increasing tailwind for example) then the aircraft will descend if it approaches the critical AoA. Flying around in alpha protection is not the best thing to do, but it is not intrinsically unsafe - GPWS, TCAS, windshear can all see the pilot make a deliberate decision to enter alpha prot. |
FF
What you said is general principle of handling with any abnormality. Screwing around with thrust levers adds another variable to the picture which you don't need. |
Ah, yes. I see what you mean.
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Thank you for the valuable interventions.
I believe the sidestick displacement needs to be forward of 10 degrees to unlatch alpha prot. now on the other side of the spectrum, 70 knot increase, would you just use speedbrake to avoid traffic conflict? |
I might be missing something here.
All this talk of Alpha Prot is interesting, but "should" not be relevant to significant short term wind change at high altitude leading to underspeed or overspeed. As in the OP's scenario of increasing tailwind, the SOPs are to descend as soon as sustained below GD and trending south with MAX THR. There should be no training of THR IDLE to counter Alpha floor. It shouldn't happen. Sure pilots should be able to recover from Alpha Floor, but that's nought to do with teaching underspeed SOPs, it shouldn't get that far. Conversely, with sudden increasing headwind - as I alluded to above - there are three events I know of, make that 4 with Vilas' example above and I am sure many more - of an aircraft exceeding MMO due sheer and ending up in Alpha Floor. So a brief overspeed leads to the protections preventing a stall? Something is wrong there, and it all seems to stem from pulling THR LVRs to IDLE and in some cases pulling backstick to keep the speed below MMO. In the overspeed situation, the 330/340 bird is tested structural integrity of Vdive of 0.93 and all aircraft are certified for short term excursions over Mmo. The wings will not fall off as soon as you go into the red. SOPs say in the overspeed if the AP drops out (Vmo+15) fly manually. Leave the A/THR ON, select a lower speed and use speed brakes if required - even if the HSP activates giving a small pitch up. From the FCTM - "ATHR engaged or setting manual thrust has the same effect on the overspeed recovery". FCTM>PR>AEP>MISC>OVERSPEED. I make no comment on the crew concerned as it was 20 years ago and I don't know what was in the A340 FCOM then regarding overspeed recovery, but in the modern day context that example would suggest a mishandling of the overspeed by the A340 crew. Overspeed condition>THR LVR IDLE>Alpha Floor in <10 seconds. Not SOP. |
That's a good point compressor stall . It's a natural reaction to want to keep out of the red band. I guess most pilots just overreact a bit when they see the speed in the red and increasing. Airbus Safety first published the VD for each model, and as you you stated, the margins are generous. 381/.89 for the A320 series.
https://safetyfirst.airbus.com/contr...eed-in-cruise/ |
As the safety first explains at high level VD is almost impossible because of the drag. It's achieved in dive at full thrust. So there's no need for over reaction. With AP& ATHR leave AP on the thrust will come back just monitor if not happy use speed brakes. If unsatisfied with ATHR then use manual thrust. There was another more recent TCAS event in A320 where the pilot disconnected the AP(cardinal error) and pulled the nose up causing RA. These panic reactions are the result of not knowing that it's not that serious. After control your speed series in Safety First the procedue was introduced in FCOM/FCTM.
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I also think there's a FOQA/FDA fear going on causing some of these events. Any red must mean tea and biccies with the CP and they avoid the overspeed at all costs...
Unfortunately the fear sets up a chain of events that leads to Alpha Floor and worse. That becomes more than one round of tea and biccies. |
Originally Posted by vilas
(Post 10837466)
There was another more recent TCAS event in A320 where the pilot disconnected the AP(cardinal error) and pulled the nose up causing RA. These panic reactions are the result of not knowing that it's not that serious.
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Originally Posted by Check Airman
(Post 10838012)
Why do you say that?
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Ah. I misunderstood what you wrote. I thought you were criticising the choice to disconnect the AP in response to the TCAS.
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A320 Stall
On A320 suppose you have engine stall after take off.After 400feet you put the thrust lever to idle on the affected engine.After this should we put the lever to MCT on good enginellevel off at 1500 feet /clean up/MCT or Mantain the flex detent or TOGA used for take off and follow the Engine out Procedure.What is the difference between MCT and T/o thrust (in flex or Toga) after 400feet?
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Originally Posted by Learningtofly85
(Post 10844103)
On A320 suppose you have engine stall after take off.After 400feet you put the thrust lever to idle on the affected engine.After this should we put the lever to MCT on good enginellevel off at 1500 feet /clean up/MCT or Mantain the flex detent or TOGA used for take off and follow the Engine out Procedure.What is the difference between MCT and T/o thrust (in flex or Toga) after 400feet?
the ENG STALL procedure will initially ask You to put the affected engine THR LEVEL at idle, i.e. procedurally and performance wise You will consider Yourself one engine out, hence follow Your engine failure after V1 procedures - check FCTM ABN/EMER PROC. ENG. Engine Failure after V1. Given the fact that prior to any action on the thrust levers You will be climbing out with 2 live engines, it is quite likely that You will reach Your normal THR RED/ACC ALT prior to any ECAM actions being conducted and You will be asked by the FMA to put the THR LEVERS to CLB and the vertical mode will revert to either CLB or OP CLB according to what lateral mode You find Yourself into (i.e. NAV or HDG). To better understand what will happen at this stage and what Your options are, go through the FCOM - Systems - 22_30 - Flight guidance. That will be helpful to better understand any further replies I believe. |
On A320 suppose you have engine stall after take off.After 400feet you put the thrust lever to idle on the affected engine.After this should we put the lever to MCT on good enginellevel off at 1500 feet /clean up/MCT or Mantain the flex detent or TOGA used for take off and follow the Engine out Procedure.What is the difference between MCT and T/o thrust (in flex or Toga) after 400feet? Following the ECAM will potentially leave you with the engine running at reduced power instead of shut down anyway, making the situation easier to handle. |
If you have Engine stall then at 400ft ask for QRH Engine stall Procedure. Leave the other thrust lever at Flex or TOGA as it is. There are three results that are possible. Common action in all three will ask you to bring thrust lever to idle. Further procedure may leave you with EFATO, partial thrust or normal thrust. Just follow the appropriate Procedure.
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Thank you everyone.
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