A330 Thrust reduction in descent?

[Speedbird744]

After watching the ITVV Airtours A330 flightdeck video, I noticed the pilots didn't idle the engines in the descent, like other airplanes do, why is this?
It must of been accelerating fast, is there an explanation why on the A330 pilots don't idle the engines in the descent?
Thanks

[OLBA18]

Haven't flown the 330 but I beleive that like the 320 it still has idle "open descent" as one form of selected flight and that the normal managed descent mode is '"des" which is based on a repressurisation segment followed by an idle path. I haven't seen the video but one explanation for non idle descent other of course than atc maybe that the descent winds were not put in or the descent wind changed to a stronger headwind.

[SFly]

There are any number of variables. One of the main ones could be that the descent was slow (ie the descent rate was not enough to give sufficient acceleration), or they might have reduced the thrust but via the autothrottles in an instance when it wouldn't be as apparant. Really there is no rule for this, just that an airspeed is usually needed to be maintained and thrust will just be adjusted accordingly. Though reducing thrust does improve economics for the airline.

I've seen it but can't remember anything about the descent. With my Sanford knowledge base I can tell you that if the descent was started around or before the BEENO intersection it may well have been quite a slow descent to landing as aircraft are at about 5000' by JESUP and by COZMO they'll have turned into final approach anyway (they used 27R if I remember correctly).

Hope this helps a bit.
SFly

[This message has been edited by SFly (edited 07 April 2001).]

[Aluminium Importer]

I have 'jumpseated' with a Virgin Atlantic captain who has participated in an ITVV video.

The videos are very detailed and informative, but I have been told that the editing can be rather dire!

You could have been watching the video where the flight should be in its descent phase, but the actual screened picture shows a clip of the a/c in its climb/cruise phase.

I may be wrong, but it has certainly happened before......

[F/O Junior]

"Idle", that means Open Descent on the A330 is a bit a pain. As long as you're descending with the speed in mach mode (selected or managed), the airplane chases its target speed with pitch inputs, which may result in overspeed. It's the same on the A32x, but it's worse on the A330 due to its inertia. Therefore many people use vertical speed for the initial descent.
And even when descending in managed mode, the engines are rearly at idle (IDLE displayed in the EWD). Thrust setting is always a bit above idle, even when flying above the profile.
During an "open descent", EPR drops below zero, and I might be wrong here, but as far as I understand the EPR definition, this means that the engine at Idle produces drag. So it might be more economical to start your descent a bit earlier with a small power setting than fly level and then have a steeper descent with more drag.
But I'm really not sure here on the last part and I'm open to any new input. I just perceived that with "managed descent" you get a shallower approach than with "open descent".

[Zeke]

Speedbird744,

On the airbus you push the power levers up to TOGA (take off/go-around) or the FLEX (flexible) gates on takeoff, bring them back to the CLB (climb) gate at 1500 feet and leave them there until the aircraft tells you to retard them when you are in the flare.

The power levers are not directly connected to the engines, when the A/THR (auto thrust) is on (normal procedure) and the thrust levers are in the CLB gate it will power up the engines if you have to climb, apply the correct amount of power to maintain altitude and airspeed in the cruise, and reduced thrust (to idle if necessary) on descent.

When the A/THR is connected the crew does not move the thrust levers at all during flight. The airbus manual describes the thrust levers as being the way pilots interface with FMGC (flight management guidance computer) and the FADEC (full authority digital engine control system), others just see them as being switches.

The A/THR has three modes, SPEED/MACH, THR (CLB, IDLE), and RETARD (IDLE).

These A/THR modes are brought to the attention to the crew by displaying messages like TOGA, MAN FLX, THR CLB, CLB SPEED, MACH, IDLE, on the PFD (primary flight display-the one with the electronic A/H), these are what is known as FMA’s (flight mode annunciators) and they tell the crew what the A/THR is doing in all phases of flight.

Others have talked a little about “open descent” this is the AP-FD (auto pilot – flight director) vertical mode, not an A/THR mode. The A/THR modes are on the top left of the PFD. The A/THR can be in IDLE mode when the aircraft is in DES (descent) or OP DESC, EXP DES, or FLARE AP-FD modes.

The thrust lever setting, and other engine parameters are on the upper ECAM screen. If you get a chance to see the upper ECAM on this video you will see a little white doughnut on the N1 (top row), this is the TLA (thrust lever angle) or more simply the position of the thrust levers, the actual N1 is displayed as both a numeric value in the center and the sweeping arm on the N1 gauge. You will notice that when the A/THR in armed, the TLA may not reflect the position of the N1, in most cases it will be at the CLB gate, and the N1 sitting further back.

:rolleyes: