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Silvio Pettirossi
21st Aug 2012, 05:07
Hello Everyone!

A question for the Bus experts around here.
You are descending below 10.000feet in DES mode and due to say, changing winds, the plane becomes a bit low on the calculated ramp and the speed bleeds off to say, 230kts. Now you approach the FMGS created ALT CSTR just before the desceleration point, the plane levels of and the thrust goes in to SPEED mode to recapture 250kts just before slowing down again do to APP FACE auto-activation. These produces a rather large power surge with the associated noise and potential PAX disconfort. Now, some of our capitains try to avoid these by activating the APP FACE earlier, while others say these fenomenom is necesary and build in to "stabilize" the engine temps for approach ore even to "de-ice" the fan blades:confused:
I find these explanations a bit strange:suspect:
I tried to find something about it on FCOMs and FCTM but was unsuccessful.
Does anybody know something about these, or is it just a myth created within our company:hmm:

outofsynch
21st Aug 2012, 07:43
I guess you mean approach phase, not face, but english isnt your first language! Good attempt.

It wont be anywhere in the manuals, but the BA 777 incident at LHR raised some awareness of the scenario of doing a long idle power continuous descent, then finding the engines wont spool up on approach.

Our company too, is encouraging a level off, or power-up before finals. More to warm the fuel heater than stabilise temps, I would have thought. Isn't that more for pistons?

STBYRUD
21st Aug 2012, 12:08
This sounds like a case of folks coming up with silly explanations for their techniques - granted, you would shed fan ice like this, but unless you have flown through proper icing conditions (when you should modulate engine thrust anyway to do just that) thats not a valid point really... The fuel icing problem on the 777 would have been even more catastrophic if they leveled off before capturing the glide wouldn't it? Three miles level, no power, no way to reach the airport.

Silvio Pettirossi
21st Aug 2012, 15:18
Oh sorry, of course I meant app phase and not face:\ I guess ICAO level 4 english has its limitations;)

Well, I am very sceptic about these one, because there are many so called "good practices" and "right techniques" around, depending on whom you fly with, that are, or not are based on airbus SOP and FCTM.

EpsilonVaz
21st Aug 2012, 16:43
Sounds like complete nonsense. As mentioned above it's just people making up reasons to explain something.

Slasher
21st Aug 2012, 20:26
The Frog's box will go from 230 to 250 kt because its a bloody computer - so
after reaching ALT CST it will immediately revert to 250/10000. Just because
the APP PHASE is only a mile or two ahead doesn't mean shmik to it. Its NOT
a pilot but a computer.

In your scenario I would've already reverted to OPEN DES to avoid a sudden
dramatic powerup, and pegged 230kts and activated the APP phase when I
decided it was time to. Anti-icing procedure is constituted during the descent
and the only time I've ever increased power to shed ice off the blades was in
a Navajo many yonks ago.

If a cadet flew a 320 like the FMC does I'd fail him.

A320baby
22nd Aug 2012, 16:00
From FL100 I normally fly the A/C with selected speed, Once I go to selected speed I immediately activate the approach phase, as a rule of thumb below FL100 I stay around 250kts, (sometimes we get high speed approved below 100) then once i'm cleared to a Altitude, say 3000ft, at 1000 to go I slow down further to 220kts then work my way to managed speed. :}

ReverseFlight
22nd Aug 2012, 16:02
Just because the APP PHASE is only a mile or two ahead doesn't mean shmik to it. Its NOT a pilot but a computer.With all due respect, there is nothing wrong with activating approach phase at the ALT CST waypoint. She'll slow to green dot (no spooling up) and you can then configure flaps in your own time.

If I spooled up at the ALT CST wpt, my checkie would fail me too ! :}

Silvio Pettirossi
22nd Aug 2012, 17:37
Most of the time I also fly 250 selectet below 10.000ft, have the app phace already activatet, and as soon as ALT* apearse on the FMA, I revert to managed speed to keep it in idle thrust all the way till gear down on the GS. But it seems like some at my company would like to fail me for AVOIDING the power surge at the desceleration point.