Hello and welcome,
Farid,
I shall speak for the A320 family. If you discuss this with pilots you will find that there are many different ideas about how to control thrust on short finals (that is, the last 4 nm). Most pilots would agree, though, that they use different techniques according to the circumstances on the day.
One thing I hope everyone would agree is that, except below 50 ft, you should never close the throttles if the A/THR is calling for thrust above idle. See (4) below.
(1) Some pilots ALWAYS use A/THR, only disconnecting it when the "gringo" shouts "
RETARD!" On an autoland, that is definitely the best technique, because the A/THR will be automatically reducing thrust to idle. Otherwise, it wastes runway, because the thrust will usually be increasing before the system calls "retard".
(2) Then there are pilots that ALWAYS use A/THR, but
– if they are doing a manual landing
– quickly close the throttle levers at about the same time as they start the flare (say, 30 or 20 feet). This works well.
(3) Then there are other pilots that ALWAYS use A/THR, but
– if they are doing a manual landing
– slowly close the throttle levers during the flare. This is not very satisfactory, in my opinion, because you cannot be monitoring the thrust indicators while you are looking out of the window. So you don't really know what the thrust is doing.
(4) Then there are those who ALWAYS use A/THR for the approach, but
– if they are doing a manual landing
– cancel A/THR at or below 200 ft.
NOTE: The problem with this is that, if you are going to keep good control of thrust during the transition, you need to watch the "doughnuts" on the thrust indicators as you pull back the throttle levers, and
– when they match the existing thrust
– disconnect the A/THR with the throttle button. During this procedure, you are not seeing the runway very well, and also vulnerable to wind shear.
(5) There are also those who
– if they are doing a manual landing and the weather is quite good
– like to disconnect the A/THR as soon as the L/G and flaps are in the landing configuration, PROVIDED they are visual with the runway by about 1000ft. If the approach has been flown up to that point using the AP, it can be useful to keep the AP until manual thrust has been established. If the runway has not been sighted by about 400 ft, they will elect to retain A/THR. See NOTE in (4), above.
(6) And finally there are those who
– if they are doing a manual landing and the weather is quite good
– like to disconnect the A/THR sometime between top of descent and before landing flaps have been set. If you do it at top of descent or in the descent, A/THR can be disconnected without affecting the thrust: merely by closing the throttle levers. Using manual thrust from way out is fine if the weather is good, traffic is light, and you and the other pilot are experienced on type and know the airfield well. Otherwise, it's not a good idea because it increases the workload of the PF at a time when the PNF is often too busy to monitor the airspeed. For the same reason, it is best to use the AP where possible, and extended use of manual thrust with AP is not to be recommended.
The A/THR on the A320 usually works very well in managed speed, when available. There is normally no argument for using it in selected speed, because you lose the protection of the excellent GS-Mini, which Airbus pioneered as an automatic system. But you must insert a sensible surface-wind (W/V) into the FMGS. On a windy day, some pilots used to be tempted to put in a stronger wind than reported, or use the gust wind. This raises the Vapp, but reduces the GS-Mini protection against a sudden loss of headwind (tailwind shear).
Finally, the A320 throttle levers are a joy to use in manual thrust
– the best of the six jet types I flew. It's a good idea to learn to use them when there is a sensible opportunity. You still use managed speed, and retain GS-Mini protection, which greatly reduces the need for thrust changes
– provided you use managed speed as a TARGET speed, not a minimum speed. Most pilots prefer to use manual thrust for single-engine work. That's partly because
– with the Airbus FBW throttle lever not being driven forwards or backwards in A/THR
– the only indication you have that the A/THR is calling for more thrust is from the gauges. It goes without saying that, every time the thrust changes on the live engine, rudder and rudder trim have to be adjusted. If you are moving the throttle by hand, you merely have to remember to move the rudder pedals slightly to reflect the throttle movement.
I have made this rather long, but hope it helps. If you are ever flying Airbuses, safe landings!
Chris
PS
I must add a caution for "young" aviators. If anything written above is in conflict with your airline's SOPs, you must follow the SOP. SOPs are designed not only to be the best way of doing things; just as importantly to avoid misunderstandings between pilots, and achieve smooth cockpit management. If you disagree with an SOP, talk nicely to them in the office.
