flyingnewbie10;
but IMO this could derive from a somewhat flawed Thrust control system in the A320
I have to say that you have seen only what you want to see in the long and detailed discussions here on the AB autothrust system and I was hoping your view would grow in the light of all the information provided by knowledgable participants/flight crews on both Boeings and Airbussi.
flyingnewbie10, there is no inherent "flaw" in the Airbus autothrottle system.
Permit me to state this a little differently:
- saying there is a flaw in the A320's autothrust system because the "autothrust system doesn't put the engine to idle thrust on touchdown" is exactly the same as saying there is a flaw in your car's gas pedal because it doesn't idle the engine when your foot is on it and you come up to a stop sign.
In a manual thrust-lever, manual landing, if you leave a thrust lever above idle thrust in a Boeing, that engine is going to stay to that setting. Same with the Airbus.
If the autothrust system is engaged on either a Boeing or an Airbus and the aircraft is being manually landed (very common situation), if the thrust levers are not pulled back to the IDLE position for touchdown and -in the Airbus, left in the CLB regime, and -in the Boeing, not disconnected, the engines will be commanded by the autoflight system to accelerate to maintain the approach bug speed. (On the Boeing I stand to be "fine-tuned" on this - it's been a while, but the general notion is, I believe, correct - tx ).
I have written in this thread that there is a caution to Airbus pilots that if the engine is started at the gate and the thrust lever is above IDLE, the engine will accelerate to the thrust lever setting. No autothrust system is going to bring the engine back to idle thrust. I suspect the same is true with the Boeing thrust levers, but someone on the Boeing can help me here with that information.
In an autoland, the Airbus autothrust system reduces engine thrust and in a "Thrust Lever Fault", the autothrust system will reduce the engine to idle thrust EVEN if the thrust lever is left in the CLB position. The lever is a thrust-"request", limited by the detent it is set in and is controlled by the autoflight/FMGC system. That stated, the airplane flies beautifully in manual thrust-lever, manual control flight.
I would like to know from a Boeing pilot if the thrust levers are moved by the autothrust system to IDLE on every landing whether it is an autoland or it is a manually-flown landing but with autothrust engaged - in other words, is the Boeing a/t system a full-time autothrust system that places the thrust levers to IDLE upon touchdown every time or will they stay in the last position they had if the pilot leaves them alone on touchdown if the autothrust is engaged for the approach, and then when the speed decays, will they move forward to maintain the bug speed? That happens on the 76' I know but I last flew a Boeing in 1991. Then, one always disconnected using the instinctive disconnect buttons but software changes - tx.
My impression from reading here and from discussing this with others is that the Boeing and Airbus systems behave in the same way in the same respective regimes described, except that the Boeing thrust levers move (reflecting the automation's 'thinking') and the Airbus thrust levers do not, (the automation's 'thinking' is reflected in the FMA and on the N1 guages).
Thanks - I hope this can be put to bed.