I agree with africanskies,
The majority of approaches I fly are handflown. Once in a while, when the weather is close to cat 1 minima I fly it sinle A/P with A/T until DH and then disconnect. Very rarely I fly a dual A/P approach.
I for one thought as well that the retard function of the A/T was only available during a dual A/P approach. I know now better!
Having immediatly dug out the manuals, nothing in there indicates that the retard funtion of the A/T is also available during a sinle A/P app. even worse, nowhere in my boeing manual it states that the A/T derives it altitude signal from the left RA (please, I looked, if someone has found were it states that let me know),
Having said that, the lack of that knowledge does not relieve one of flying the plane. The fact that the A/T commanded idle thrust at that point is something one would normally expect anyways, you intercept the G/S, command gear down, flaps 15 and set f15 speed or 160 ( depending on sop) and then getting close to 160 or F15 speed to call for flaps 30 set fas. Even disregarding the FMA annunciations one would expect when the speed approaches fas the A/T to increase thrust. monitoring speed at that point during the app is pretty basic.
What if after G/S intercept and the A/T moving to idle the A/T for some inexplicable reason had clicked of, the same would have happened in this case. Why? The pilots where not monitoring the instruments.
Simple in this case, the automation did something unexpected and the pilots did not catch it.
I for one learned some valuable lessons. For one I thought the retard funtion of the A/T was only available during a dual A/P approach and even with hindsight the boeing books don't indicate otherwise.
the argument used a few post back:what would you expect it to do, maintain mcp speed until touchdown. Frankly, that's exactly what I would have expected because boeing doesn't want you to leave it engaged until touchdown on a single A/P approach. that some hero pilots knew better because they tried it in the sim, well, woopief@ckingdoo to them. The normal line pilot doesn't know this because it's not in any boeing approved training program. Seriously,I would like to have a show off hands of the number of pilots that knew this! and then my next question: if you are flying enroute and the left RA would have a hickup and indicate -8 would the A/T go in retard mode as well or does this only happen after G/S intercept. I can't get this out of the manual neither!!
The normal line pilot should however know to monitor basic instruments.
Anyways, now we know what happened. The only interesting thing left is why? Why did 3 experienced pilots fail to realise that the airspeed dropped 40 kts below ref.
Last edited by flyburg; 5th Mar 2009 at 21:55.