F speed too low?

[sidestickbob]

Hi all,

I've been flying the A320/321 for a number of years now. On final to XXX the other day I reduced to F speed in CONF 2 (with the gear UP). There was a fair bit of convection and turbulence. The speed dropped below F speed and into VLS. The aurtothrust was miles behind the situation by leaving the engines at idle for what seemed like an eternity. We're not supposed to "phase advance" at our company any more and I was so concerned about how things were panning out that I ended up going around.

I've always thought that F speed is too low. It tends to result in very high pitch attitudes which when combined with turbulence and slow autothrust seem to make some approaches quite exciting!

I'm interested in the thoughts of any other bus drivers.

Cheer's

[sabenaboy]

Dear Sidestickbob,

I'd say there's nothing wrong with "F-speed" in the case you describe, but A/T is to blame for not keeping it!

Are you flying in a company where A/T is mandatory at all times (and an A/T failure would be a major emergency?) If so, that's a shame.

If however you are allowed to use manual thrust in the Airbus, please make sure that you get enough practise to use it with confidence!

Believe me: after a little practise, any pilot will manage the thrust better manually then the A/T system.

Please read this earlier post (http://www.pprune.org/tech-log/414315-a320-how-save-landing-2.html#post5677745) I made about A/T use in the Airbus.

Regards,
Sabenaboy

[hetfield]

If I remember correctly SOP in our company was F +20 in Config 2.

[I-2021]

I've always thought that F speed is too low. It tends to result in very high pitch attitudes which when combined with turbulence and slow autothrust seem to make some approaches quite exciting!

I'm interested in the thoughts of any other bus drivers.

The aerodynamics and fly by wire flight controls combination on second generation Airbus gives you the opportunity to fly a variety of operational speeds at different configurations. In some turbulent conditions with gusty winds, it is important to adapt the combination of speed/attitude/configuration to the actual condition in order to have the greatest margin of reaction. The autothrust will do a great job if the energy of the airplane is well maintained, and in that case it is worth having some extra speed to play with the gusts given your relatively high pitch up attitude at the F speed. When it's gusty, I usually tend to keep at least 160 kts with F2, in my opinion going below that is so close to your Vapp that I prefer to complete the configuration and have a stable and well trimmed airplane at low speeds. Of course, if the ATHR response is unsatisfactory I takeover, but I have to say that the system really works very well in a very wide range of operational environments.

[Microburst2002]

Hi

Have you checked if there is a noticeable difference between FAC computed green dot, F,S and VLS and FMGC computed ones? If this difference is similar from flight to flight in the same airplane and in the same sense (FMGC speeds 5 to 10 kt faster than PFD speedstand you notice less speed stability and more difficult flares) then that airplane can have a problem with teh probes or the computers.

If this is the case, fly at the FMGC speeds and change VAPP accordingly so you can benefit from GS mini.

Sabenaboy:

I wish my airline was like yours. I have met quite a few former sabena captains and they all love hand flying and I think they are probably the best captains I have flown with in all aspects.
cheers

[PantLoad]

My opinion, that's all,

The Bus is a great flying airplane. It's well-balanced,
aerodynamically-honest.

And, remember the eight Airbus Golden Rules....one of which is
(paraphrase)....If the thing ain't doing what you want (or expect),
take over.

My old airline 'discouraged' flight without the A/Thr. In fact, it was
prohibited unless there was some sort of abnormal or problem.
That's OK....I can live with that....but, again, if you have to reduce
the level of automation to get the job done, no one in his right mind
can gig you for doing what you need to do. Certainly, if the paper
pushers want to discipline you for such action, a call to the FAA
and the NTSB will hammer the ignorance quickly.

BTW, those eight golden rules are available on-line....always good
to review.


Fly safe,

PantLoad

[tom775257]

When flying the A320/1 as per the poster above

<<When it's gusty, I usually tend to keep at least 160 kts with F2,>>

I always select speed now if not doing a gradual decel/ CDA and never let the aircraft get to F speed with F2. At 160kts you get a nice buffer. Personal preference I know but works well for me, I hate being at high pitch attitude low speed with lazy autothrust. Flying a 321 into AGP the other day, Conf2, 160 selected, the aircraft went back to just above VLS before deciding to add a handful of thrust.

I must add I also dislike the last minute take over of auto to manual thrust when it doesn't perform well on the Airbus. I find the majority of times it tends to destabilise the approach, B737/757 etc. are much more intuitive having the throttles in the correct position vs. matching the donut with the thrust lever angle etc. whilst being worried about airspeed on the Airbus.

Finally I would add that phase advance often ends in a balls up too from my limited experience... people click forward, nothing happens for a while, then whooshh.... click back...unstable...G/A. Also seen a Captain try a phase advance below 100'RA which went even worse.

[rudderrudderrat]

Hi tom775257,

OEB 827/3 removed that procedure. (I agree - it is a pity we don't have back driven TLs - it would make it much easier.)

"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."

[Dan Winterland]

Wise words - phase advance is not a great idea and I have seen it go badly wrong more than once. People were too keen to use it.

If I don't like the speed it gives me, I either manually select a speed until I'm happy, or use manual thrust. Many of the approaches I do are speed controlled up to a certain DME from touchdown anyway - so the choice is made for me.

And if in a V2500 powered A321, man thrust is my preference anyway as IMHO, the software is often not proactive enough in gusty or turbulent conditions.

[Microburst2002]

In every approach I check FMGC VLS when in full flap, and compare with PDF¡'s VLS. Usually PDF's is two or three knots slower (safe side). Probably because the airplane is not as heavy as FMGC thinks, or who knows. Sometimes the difference is large and I immediately notice it during the flare (long, with relatively low pitch attitude)

But if PDFs is higher, then I add knots to the VAPP in the FMGC as necessary.

If in a given airplane the difference is always the same, there is something wrong with teh AoA probes or computers, and is wise to add knots to VAPP accordingly.

[PENKO]

Sidestisckbob, in stead of going around, why did you not just disconnect the autothrust? Pull the levers back to 70%, click off the AT, presto. I don't like the pitch attitude either at F speed, but my feeling is that going around from that position has more pitfalls than just manually taking over the thrust.

[Slasher]

I think this should be nailed to every Airbus cockpit.....

http://t0.gstatic.com/images?q=tbn:ANd9GcQ6qgRrDudrNzyyJGXkTcnpxOqJRBrUMWUaeVkirFI UKnxhvXVY

It answers a lot of questions like this one - if you're not satisfied
with the speed its flying, take out the damn thing and control it
yourself.

In any case GWFK and AOA readouts in that PARAM ALPHA will
confirm whether the FACS are doing their stuff or not. If AOA is
reading something silly, go for FMC speed. If that's not healthy
then pull out the QRH and go selected with A/T off.

I do more selected speed approaches in this thing with A/T off
than any other modern jet type I've flown. GS mini has a purpose
but only up to a point.