Originally Posted by
vilas
Day in day out people are flying pitch for GS and thrust for speed. If you raise the pitch off course the speed will decrease so thrust will be increased simultaneously unless your speed is high and you want to loose it. SFO they were on verge of stall so let's not talk about it.
Thee are two separate but related things going on in is discussion, that it would help to untangle and look at separately. (Though they are occurring simultaneously)
First is the pilots’ intent of what the pitch is to achieve, which is something occurring in their heads. Yes day in and day out they are pitching for path, I don’t doubt that.
But, second, is the physical fact that AOA determines airspeed and pulling on the elevator controls airspeed downward. This is true 100% of the time, whether in a minor GS deviation in a normal approach, or what happened at SFO. I stress again that there is no difference in concept, only a difference in degree which is irrelevant. So the SFO event
must be talked about, because it is a function of the same laws of flight dynamics, long before they approached a stall.
On a normal approach half a dot low, if the pilot pulls the elevator back a tiny bit to raise the nose a fraction of a degree, his intent is to adjust the path, which will happen successfully; but, simultaneously, the increased AOA
is commanding an airspeed reduction. Whether he intends it or not, whether he’s aware of it or not, it
is happening. If everything goes normally, he will increase thrust commensurately with the shallower path and return the elevator to the original position, commanding the wing to the original AOA, and the airspeed to the original value. Hunky dory.
But if he doesn’t come in with thrust and continues to pull the elevator back commanding a higher AOA and a lower airspeed, even by 5 knots, that is the SFO sequence. There is no dividing line. Where would such a line be, between 5 knots and 31? 10? 15? 16? No, The SFO sequence was a manifestation of the exact same flight mechanic as normal flight. Every time you pull on the elevator, no matter how slightly and how day-to-day, you are commanding an airspeed reduction and potentially entering that same loop. And to disregard the relevance of the fact that you’re doing that (regardless of that you’re primarily using AOA for something else at the same time), is to make the same mistake that the Asiana pilot did.