Airbus autothrust setting on final

[Duckjibe]

I've a bus driver question:

Sometimes, during (nicely) stabilized final approaches, on path, ATHR ON (FMA= Speed, (but no autoland planed)),
under some weather conditions, IAS drops below Vapp, sometimes even down to VLS.

When below 500' AAL, but beyond 50' (Let's say: beyond flare height range)
What is the best corrective action?

:suspect:...Nothing, just wait and see...and feel uncomfortable (Who cares! this thing is certified)

:{...Go around!

:E...Disconnect ATHR, and manually adjust thrust (Back to basics)

:hmm:Slightly and briefly,
to get out of climb notch, (which takes you beyond ATHR range), thus trend very briefly to MCT thrust,
then throttle back (a very short while after) to initial climb position, when a proper IAS is recovered.
(Is what I was taught under line training)

Any Airbus (or other) documentation on that matter?
:}Many thanks in advance for answers

[Nubboy]

Our stable approach criteria are Vapp +10 / -5 kts.
Normally Vls is Vapp -5, so Vls just meets the criteria. However, whats the speed trend doing, and how slow is the autothrust in reacting? The -5 isn't neccessarily the end of the world in itself.

[Artificial Horizon]

Just 'pull' for selected speed at the Vapp. Normally just by pulling selected speed it somehow 'wakes' up the autothrust when it is acting a bit lazy. If that doesn't do it then just use manual thrust.

[Slasher]

Slightly and briefly,to get out of climb notch, (which takes you beyond ATHR range), thus trend very briefly to MCT thrust, then throttle back (a very short while after) to initial climb position, when a proper IAS is recovered. (Is what I was taught under line training)

Yeh I do that all the time and it works too! Saves a lot of bloodey knob-pulling. Found the newer IAEs are more suseptable to this decay of speed than the older CFMs I used to fly. Dunno why.

[longarm]

push levers forward out of climb gate and then quickly back in. This will give an immediate thrust increase. Known as "phase advance". Don't try below 100'.

[rudderrudderrat]

Hi longarm,

My FCOM still has this OEB. Has it been removed from yours?

Oeb N° 827 Revision 3
Release Date 1-Jan-2009
Subject AIRCRAFT HANDLING IN FINAL APPROACH
Reason During the approach, with the A/THR active, Airbus recommended to set the thrust levers above the CL detent (but below the MCT detent), in exceptional circumstances, if the speed significantly dropped below Vapp. However this procedure is not trained and proved to have more drawbacks than advantages. Therefore, Airbus no longer recommends to use this procedure. The procedure is deleted from the operational documentation. If the A/THR performance is not satisfactory, the flight crew should take over, and control the thrust manually

[Aviophage]

Don't ever try and correct this by pushing the throttle up a notch when close to the ground, like the original poster has stated. This may lead to a speed increase above V(app), pitch up and a rate of descent decrease. Then you could be above the glideslope and risk landing further down the runway.

If this situation occurs, I would call unstable and declare a go-around quickly.

[shortfuel]

A/THR is optimized to work with AP ON.
When you manually follow FDs on final and decided to keep the A/THR ON, you do not need to do anything if your IAS is between Vls and Vapp+10 (I assume you're on the ILS...).

This situation is usually transient and that's why we add +5kts when A/THR is ON for APP.

On the A330, it's really not unusual to fly the entire APP with Vapp-X when A/THR is ON.
Personally, I don't like it, so A/THR is OFF most of the time.

So to answer your question, I'd say it depends on your energy state: flight path deviation/ROD/current wind/expected wind/thrust demand ordered by A/THR/height...

[chin]

Simply ask your fellow monitoring pilot to put 2 KTS more on the PERF-PAGE.

chin

[divinehover]

Longarm is correct. Crack the T/L's out of the climb detent for a couple of seconds. Easy and involves the least amount of button pressing and all reverts to normal within a few seconds.

DH

[Duckjibe]

:) Many thanks for comments and references, folks!


"push levers forward out of climb gate and then quickly back in. This will give an immediate thrust increase. Known as "phase advance". Don't try below 100'.."
:EDoes anybody know about the outcome, if tried below 100', concerning this method ???:}

[rudderrudderrat]

If you were controlling thrust manually, would you really advance the thrust levers to MCT just to recover a few kts?

"phase advance" has been deleted from my copy of FCOM.

[shortfuel]

"Phase advance" has been deleted from all up-to-date FCOM / FCTM.

Depending on your variant, msn and engines, if you still elect to use the "phase advance" technique, in some cases (old CFM msn) A/THR will disconnect and remain disconnected below 100' RA...in that case good luck to you to recover a positive speed control before you touch the surface of the Earth.
In other cases (latest IAE), A/THR will reactivate as soon as your thrust levers are back at or below CL detent.