Few basic questions about A320
Pilots who have flown Boeing do not like Airbus GS mini until they get their heads around it. They are nervous when the Airbus GS mini takes power off with a decreasing headwind, because that is opposite to what the Boeing will do. I flew with an ex Boeing guy once who wanted to use selected speed "to avoid it taking power off" during a turbulent approach. I managed to talk him out of it, by pointing out that it could be dangerous to effectively disconnect the GS mini.
Airbus A/THR can seem lazy, but of course it cannot anticipate, and presumably does everything at 1g. As long as the GS and base energy is maintained all is good. Manual thrust can of course be used but you must still follow GS mini, which can be quite lively !
Airbus A/THR can seem lazy, but of course it cannot anticipate, and presumably does everything at 1g. As long as the GS and base energy is maintained all is good. Manual thrust can of course be used but you must still follow GS mini, which can be quite lively !
Quote from Uplinker (my emphasis):
"Manual thrust can of course be used but you must still follow GS mini, which can be quite lively !"
On the contrary! I did the majority of visual approaches with manual thrust in all wind conditions. It was far easier than on previous types that lacked GS-mini. Very few power changes were needed to follow the target IAS, for the very reasons FlightDetent and I have explained above..
"Manual thrust can of course be used but you must still follow GS mini, which can be quite lively !"
On the contrary! I did the majority of visual approaches with manual thrust in all wind conditions. It was far easier than on previous types that lacked GS-mini. Very few power changes were needed to follow the target IAS, for the very reasons FlightDetent and I have explained above..
Last edited by Chris Scott; 4th Dec 2016 at 21:58. Reason: Amending Uplinker to FlightDetent in final sentence.
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Airbus A/THR can seem lazy, but of course it cannot anticipate, and presumably does everything at 1g.
Fair enough, I wasn't sure, hence 'presumably'.
The A330 A/THR seems particularly lazy (slow to react) to me.
The A330 A/THR seems particularly lazy (slow to react) to me.
Only half a speed-brake
when the Airbus GS mini takes power off with a decreasing headwind
HW decreases, IAS drops. Vtarget drops too, by the very same amount. Thrust remains the same.
Hi Flight Detent,
(Apologies for mixing you and Uplinker up in my previous post, now amended.)
Quote:
"HW decreases, IAS drops. Vtarget drops too, by the very same amount. Thrust remains the same."
Yes. GS-mini commands a constant ground-speed until the flare, meaning a constant VS. Assuming no up or down drafts, thrust can remain the same during sudden changes of headwind, for the reasons stated.
However, I think what Uplinker may have in mind is a point that I made in a previous post. As the target IAS reduces, the thrust needed to sustain it in the medium term will slightly reduce. For example, you need more thrust to fly a steady 170 knots than a steady 140.
(Apologies for mixing you and Uplinker up in my previous post, now amended.)
Quote:
"HW decreases, IAS drops. Vtarget drops too, by the very same amount. Thrust remains the same."
Yes. GS-mini commands a constant ground-speed until the flare, meaning a constant VS. Assuming no up or down drafts, thrust can remain the same during sudden changes of headwind, for the reasons stated.
However, I think what Uplinker may have in mind is a point that I made in a previous post. As the target IAS reduces, the thrust needed to sustain it in the medium term will slightly reduce. For example, you need more thrust to fly a steady 170 knots than a steady 140.
Only half a speed-brake
Dawned on me just after I submitted the last post, but was too lazy to edit. I had skipped reading that previous one of yours, seeing it was address to someone else. Apologies, will try harder starting already tomorrow! 
G'nite and thanks.
G'nite and thanks.
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you need more thrust to fly a steady 170 knots than a steady 140.
Quote from rogerg:
"Depends maybe, the same AC at 140 will need a higher angle of attack so maybe drag will be greater = more thrust."
As 140 kt is a typical Vapp on an A320 at a fairly high weight, that would suggest that the a/c is flown routinely below its minimum drag speed for Flaps Full and L/G extended. Can't quote you any figures, but I can assure you that is not the case. Speed stability is the norm on aerodynamically-conventional types (which the A320 definitely is).
IIRC, the only Western airliner certificated to fly approaches on the "wrong" side of the drag curve was the slatless, flapless Concorde.
"Depends maybe, the same AC at 140 will need a higher angle of attack so maybe drag will be greater = more thrust."
As 140 kt is a typical Vapp on an A320 at a fairly high weight, that would suggest that the a/c is flown routinely below its minimum drag speed for Flaps Full and L/G extended. Can't quote you any figures, but I can assure you that is not the case. Speed stability is the norm on aerodynamically-conventional types (which the A320 definitely is).
IIRC, the only Western airliner certificated to fly approaches on the "wrong" side of the drag curve was the slatless, flapless Concorde.
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Speaking of flying the aircraft manually with all the automatics off, My brother (737 Captain) told me recently he does this quite often to "keep in practice", often to the surprise/ consternation of the FO. Brother is a little concerned that some of his colleagues have no interest/ confidence is doing same. Should that be concerning, is it unusual for a pilot to want to manually fly the aeroplane and is it a skill all should practice?
Thanks
Michael
Thanks
Michael
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the GS-MINI may cause the IAS target to shoot up above the Flaps Full limiting speed
I doubt about that because:
The IAS targets have 2 limits:
‐ VAPP as minimum value
‐ VFE-5 kt in CONF FULL, or VFE of the next configuration in CONF 1, 2 or 3 as the maximum
value. According to FCOM DSC22
So GS-MINI wouldn't make the target speed to shoot up the limitation of Vfe.
But I can't understand "The purpose of the ground speed mini function is to take advantage of the aircraft’s inertia when the wind conditions vary during the approach". I thing GS-MINI just enegy keeper, how can related to inertia?
The IAS targets have 2 limits:
‐ VAPP as minimum value
‐ VFE-5 kt in CONF FULL, or VFE of the next configuration in CONF 1, 2 or 3 as the maximum
value. According to FCOM DSC22
So GS-MINI wouldn't make the target speed to shoot up the limitation of Vfe.
But I can't understand "The purpose of the ground speed mini function is to take advantage of the aircraft’s inertia when the wind conditions vary during the approach". I thing GS-MINI just enegy keeper, how can related to inertia?
Welcome Jay Li !
Quotes:
"So GS-MINI wouldn't make the target speed to shoot up the limitation of Vfe."
You are right, according to vilas - who already corrected me. But, in my days on the A320 (1988 - 2001), it often did because the software modification to prevent that happening had not been introduced.
"But I can't understand 'The purpose of the ground speed mini function is to take advantage of the aircraft’s inertia when the wind conditions vary during the approach'. I think GS-MINI just energy keeper, how can [it be] related to inertia?"
I also disagree with the sentence you have quoted, so I very much hope I didn't write it!
They are certainly not the same, although related. As you know, in Dynamics, inertia is simply the same as mass (M). Kinetic energy is 0.5 Mv^2. The velocity (v) is, in our case, the ground-speed.
On the approach GS-mini stops the ground-speed (and, therefore, the kinetic energy) falling below the value which will be needed when the aircraft crosses the runway threshold. So it's a safer way of managing energy than selected speed, where kinetic energy will have to be added - using a thrust increase - if and when the headwind reduces.
Using selected speed, if the loss of headwind is large and sudden, the IAS will temporarily fall below Vapp, and maybe even below VLS, before the added thrust has time to increase the ground-speed (and, therefore, the kinetic energy) to where it needs to be. The greater the mass (all-up weight) of the aircraft, the longer it will take for a given thrust increase to do the necessary work. If the loss of IAS happens at a very late stage of the approach, an undershoot and/or hard landing is the likely result - so of course a go-around may be necessary.
Quotes:
"So GS-MINI wouldn't make the target speed to shoot up the limitation of Vfe."
You are right, according to vilas - who already corrected me. But, in my days on the A320 (1988 - 2001), it often did because the software modification to prevent that happening had not been introduced.
"But I can't understand 'The purpose of the ground speed mini function is to take advantage of the aircraft’s inertia when the wind conditions vary during the approach'. I think GS-MINI just energy keeper, how can [it be] related to inertia?"
I also disagree with the sentence you have quoted, so I very much hope I didn't write it!
They are certainly not the same, although related. As you know, in Dynamics, inertia is simply the same as mass (M). Kinetic energy is 0.5 Mv^2. The velocity (v) is, in our case, the ground-speed. On the approach GS-mini stops the ground-speed (and, therefore, the kinetic energy) falling below the value which will be needed when the aircraft crosses the runway threshold. So it's a safer way of managing energy than selected speed, where kinetic energy will have to be added - using a thrust increase - if and when the headwind reduces.
Using selected speed, if the loss of headwind is large and sudden, the IAS will temporarily fall below Vapp, and maybe even below VLS, before the added thrust has time to increase the ground-speed (and, therefore, the kinetic energy) to where it needs to be. The greater the mass (all-up weight) of the aircraft, the longer it will take for a given thrust increase to do the necessary work. If the loss of IAS happens at a very late stage of the approach, an undershoot and/or hard landing is the likely result - so of course a go-around may be necessary.
