Autothrust Confusion
Quote from fredgrav:
I was referring to an AP OFF + FD + ATHR ON condition: here the A/THR is still in THRUST mode. In THRUST mode the AP pitch mode maintains speed, but as it is not ACTIVE, unwanted thrust excursions may verify while flying manually. It is advisable at this purpose to turn FD's OFF in order to revert from THRUST MODE to SPEED mode, where ATHR maintains a constant speed (selected). Surely radar vectors are easier with FD ON, but if you are being vectored, and flying with AP OFF, FD should also be selected OFF, and FPV alone might help you keeping the path ...
[unquote]
Can an old fart be permitted a few remarks, to challenge statements that are admittedly off the original topic? As a long-retired A320 driver (Jan1988 - Nov2001) I've been trying to keep my oar out of this thread, but the above remarks seem to betray a big misunderstanding of the A/THR modes. What exactly do you mean by "THRUST MODE"?
On the initial approach, the only thing that will prevent the A/THR being in "SPD" mode is if the FD has been left in "DES" mode or "OP DES" mode. The A/THR mode will then be "IDLE". If at this stage the pilot goes visual, ignores the FD commands (while leaving the FD on), and sooner or later starts to reduce the rate of descent, the A/THR will continue to command idle thrust. This was the prime reason for the Indian Airlines Lahore (?) accident circa-1989, but others had previously fallen (nearly) into the trap. THAT is the scenario in which you MUST turn the FDs off (although improved low-speed protections were installed after that accident).
With AP off, I agree that – any time you are not on radar vectors or flying an ILS – the FD should be switched off, and "SPD" mode of the A/THR verified (assuming you are using it). The "bird" is to be recommended.
On final approach, using auto-thrust, some of the commanded thrust changes can be unnecessary, particularly in gusts. On a single-engine approach, in particular, unexpected thrust changes make smooth yaw-control difficult. A stickler for SOPs, I hope nevertheless that there are still some A320 fleets sufficiently enlightened to permit their pilots the choice of manual thrust, on short-final at least? The A320 manual throttle is the best of the six jet types I flew. But in auto-thrust, the absence of tactile information (throttle movement) is a drawback, as we tried to convince Bernard Ziegler in 1986...
Chris
PS:
tom775257, see you got in first!
fredgrav, I have just looked at your personal profile. I hope the above is helpful, and that you soon enjoy flying Airbus FBW.
Last edited by Chris Scott; 7th April 2010 at 14:06.
Reason: PS extended.