Selected Speeds on A320
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The earth is littered with broken airplanes and broken bodies flown by pilots who thought they were smarter than the aircraft manufacturer, regulatory authority and their own training department.
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vilas
Hello there,
(For Direct Law Airbus recommends use of manual thrust.)
The technical reasons for using Selected speed for VAPP with LDG with S/F jammed are the following:
1. The selected LDG CONF on the MCDU may not correspond with the actual Flaps lever position for landing. This could limit your Managed Speed target to F, which could be above your abnormal VAPP. (i.e. no deceleration to Vapp tgt)
2. VFE exceedance, due GSmini, whenever the actual CONF (due jam) is higher than the Flaps lever position for landing. (i.e. the actual VFE is lower than the one displayed on the PFD speed tape)
It is true that high-energy during last stage of final approach can be avoided by not having GSmini, although for the A330, A320neo and A350 with k-factors significantly reduced this is much less of an issue than with the A320ceo.
Indeed, in the case of a G/A with S/F jammed, selected VAPP will become managed upon SRS engagement. Speed will have to be Pulled upon reaching Acceleration Altitude. (Top-tip: Speed can be inserted as a SPD constraint in the missed app, as a reminder)
Hello there,
(For Direct Law Airbus recommends use of manual thrust.)
The technical reasons for using Selected speed for VAPP with LDG with S/F jammed are the following:
1. The selected LDG CONF on the MCDU may not correspond with the actual Flaps lever position for landing. This could limit your Managed Speed target to F, which could be above your abnormal VAPP. (i.e. no deceleration to Vapp tgt)
2. VFE exceedance, due GSmini, whenever the actual CONF (due jam) is higher than the Flaps lever position for landing. (i.e. the actual VFE is lower than the one displayed on the PFD speed tape)
It is true that high-energy during last stage of final approach can be avoided by not having GSmini, although for the A330, A320neo and A350 with k-factors significantly reduced this is much less of an issue than with the A320ceo.
Indeed, in the case of a G/A with S/F jammed, selected VAPP will become managed upon SRS engagement. Speed will have to be Pulled upon reaching Acceleration Altitude. (Top-tip: Speed can be inserted as a SPD constraint in the missed app, as a reminder)
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OP DES
Except that the FCTM says selected speed must be flown there's no reason given as to why. So if you have any document it would be nice to have. As far as Direct Law is concerned except B+G where STATUS tells you to switch off ATHR I haven't seen anything regarding G+Y or any other. Rather explaining abnormals it says even with loss of AP, the ATHR may be available. Although I can see some merit in manual thrust. The GS mini activation as a cause we are offcourse logically guessing. But strange as it may sound the ATHR has nothing to do with GSmini function. GSmini requires only APP phase and Managed speed. So, even if you switch off the ATHR your Vapp will shift but it will not be flown since thrust won't respond to it, unless you move it manually. When under pressure of abnormalities flying 15 or 20 kts below Vapp will make anyone very uncomfortable. Only Select Speed will freeze the Vapp target. Good to have any other information.
Except that the FCTM says selected speed must be flown there's no reason given as to why. So if you have any document it would be nice to have. As far as Direct Law is concerned except B+G where STATUS tells you to switch off ATHR I haven't seen anything regarding G+Y or any other. Rather explaining abnormals it says even with loss of AP, the ATHR may be available. Although I can see some merit in manual thrust. The GS mini activation as a cause we are offcourse logically guessing. But strange as it may sound the ATHR has nothing to do with GSmini function. GSmini requires only APP phase and Managed speed. So, even if you switch off the ATHR your Vapp will shift but it will not be flown since thrust won't respond to it, unless you move it manually. When under pressure of abnormalities flying 15 or 20 kts below Vapp will make anyone very uncomfortable. Only Select Speed will freeze the Vapp target. Good to have any other information.
Last edited by vilas; 2nd Aug 2021 at 07:04.
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Hi vilas
Thanks for your reply.
Two reasons I gave I cannot give you a reference for, sorry. But let’s say that it is pretty reliable.
Indeed, only G+B SYS LO PR mandates A/THR OFF due to reduced pitch authority to counteract pitch-power couple.
A/THR off for Direct Law is recommended though as per L2 note in FCOM-PRO-ABN-F/CTL-DIRECT LAW.
Well aware of GSmini not being related to A/THR.
Thanks for your reply.
Two reasons I gave I cannot give you a reference for, sorry. But let’s say that it is pretty reliable.
Indeed, only G+B SYS LO PR mandates A/THR OFF due to reduced pitch authority to counteract pitch-power couple.
A/THR off for Direct Law is recommended though as per L2 note in FCOM-PRO-ABN-F/CTL-DIRECT LAW.
Well aware of GSmini not being related to A/THR.
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OP DES
Thanks found it. It's other way round, use of manual Thrust is recommended. But it doesn't appear in STATUS for failures.
Thanks found it. It's other way round, use of manual Thrust is recommended. But it doesn't appear in STATUS for failures.
Last edited by vilas; 2nd Aug 2021 at 03:59.
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OP DES
It's strange that actual failures (except HYD G+B) which put the aircraft in Direct Law does not mention anything about use of manual thrust in the STATUS of the failures. And except dual RA failure no one reads the FCOM for Direct Law. So a question arises, is Airbus really serious about manual thrust in Direct Law?
It's strange that actual failures (except HYD G+B) which put the aircraft in Direct Law does not mention anything about use of manual thrust in the STATUS of the failures. And except dual RA failure no one reads the FCOM for Direct Law. So a question arises, is Airbus really serious about manual thrust in Direct Law?
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Hi Vilas,
As you know the Summary is a tool to manage the workload during a complex failure when time is critical.
The Summaries contain the minimum information to get the aircraft on the ground safely. In fact some procedures embedded in the Summary have been greatly reduced of information given the context of an already high workload vs time-criticality.
A ‘blanket’ recommendation to use manual thrust when in Direct Law does not fit in the philosophy of a Summary, after all it is not prohibited: hence safe enough and not worthy of mention in the Summary.
If remembered and applied by the crew as a technique, it’s a bonus.
Sorry, just read you were talking about the STS page. Same applies there to a certain extent, STS does not mention recommendations.
G+B is a special case due handling degradation in addition to the obvious F/CTL law degradation.
As you know the Summary is a tool to manage the workload during a complex failure when time is critical.
The Summaries contain the minimum information to get the aircraft on the ground safely. In fact some procedures embedded in the Summary have been greatly reduced of information given the context of an already high workload vs time-criticality.
A ‘blanket’ recommendation to use manual thrust when in Direct Law does not fit in the philosophy of a Summary, after all it is not prohibited: hence safe enough and not worthy of mention in the Summary.
If remembered and applied by the crew as a technique, it’s a bonus.
Sorry, just read you were talking about the STS page. Same applies there to a certain extent, STS does not mention recommendations.
G+B is a special case due handling degradation in addition to the obvious F/CTL law degradation.
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but I can’t find any reference today.
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Golden rivette
The reference for Direct Law is given by OP DES. The problem is aircraft just doesn't transit by itself to Direct Law but it's the result of other multiple failures. There is no point giving the information in Direct Law which no one reads. The STATUS of the failure should ask you to switch off the ATHR. Unless it's a personal choice as is in the case of OEI. The reason for recommendation of manual thrust is understandable. In Direct Law the aircraft switches from flight path stable to conventional speed stability. So it's liable to pitch up with thrust changes like B 737, A310, A300 so if AP off, then ATHR OFF.
The reference for Direct Law is given by OP DES. The problem is aircraft just doesn't transit by itself to Direct Law but it's the result of other multiple failures. There is no point giving the information in Direct Law which no one reads. The STATUS of the failure should ask you to switch off the ATHR. Unless it's a personal choice as is in the case of OEI. The reason for recommendation of manual thrust is understandable. In Direct Law the aircraft switches from flight path stable to conventional speed stability. So it's liable to pitch up with thrust changes like B 737, A310, A300 so if AP off, then ATHR OFF.
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It’s a recommendation only, so it will never become an action-line. (Except for G+B) Not in the Summary nor on the STS page. There are cases where you’d want to keep the A/THR on against the general recommendation.
Airbus will never explicitly ask you to switch off a system that is still available and certified for use.
Airbus will never explicitly ask you to switch off a system that is still available and certified for use.
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As mentioned, ATHR is not ‘failed’ in direct law. It’s only a technique to manage the pitch/power couple. Have you tried flying with the autothrust engaged in the sim when in direct law? It’s harder than it looks! For a start, you’re having to predict what the autothrust is going to do and you have to keep scanning the engine instruments to anticipate the pitch/power couple, then make the pitch correction, then trim. If it’s a gusty day, the autothrust will start hunting the speed and it will destabilise you potentially even causing PIO.
It is far, far, far easier to set a datum with the thrust levers, disconnect the autothrust and be in total control of the aeroplane. Making as few thrust changes as possible is the key to flying a stabilised approach in direct law.
It is far, far, far easier to set a datum with the thrust levers, disconnect the autothrust and be in total control of the aeroplane. Making as few thrust changes as possible is the key to flying a stabilised approach in direct law.
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I agree and said the same thing but an important recommendation should also be in the STATUS as "Consider Manual Thrust" or discussed in FCTM. Hardly any pilot if at all gets the experience of Direct Law in real life so it remains a simulator exercise but many Pilots who are exposed to G+Y fail in recurrent don't use manual thrust.
