On Wednesday, 10 July 2013 22:13:56 UTC+8, wrote:
The news about the B777 accident at SFO....Is there something fundamentally different about airspeed control in large jet aircraft?

I learnt to fly GA aeroplanes where Attitude for Airspeed, Power for Rate of Descent was taught for the approach. This same school taught Pitch for Path, Power for Airspeed once you got into their high performance aircraft. So even within the one establishment, variation raged as Dean suggests below. The felt that the former was safer for ab-initio students. In my airline career the latter has been taught and whilst I personally prescribe to the latter, I honestly don't think it matters too much due to the inter-relationship between the two. In a powered aircraft, if you are low on approach and pitch the nose up to correct, you're going to have to add power to maintain airspeed. Alternatively, if you are low on approach and add power to correct, you're going to have to pitch the nose up to maintain airspeed.

In a transport category jet at flight idle for descent, speed is controlled by pitch/attitude. When I was flying Embraer 170's they went as far as to call this "Speed on Elevator" (Where the alternative, speed controlled by engine thrust, was called "Speed on Thrust"). This is where a jet aircraft behaves exactly like a glider. Things change however, on an approach such as an ILS. Notwithstanding deceleration for configuration (gear and flap extension) a correctly flown ILS will be flown with pitch/attitude controlling the flightpath and thrust controlling airspeed. This is accomplished by the Autopilot and auto-throttle in concert. The auto-throttle is like a smart version of the cruise control in your car. It will command the required thrust to achieve the target speed which in the latter part of the approach was Vref, the target approach speed.

In a Boeing, the throttles are backdriven by the auto-throttle. This means that unlike an Airbus, electric motors cause them to move in response to commanded changes in thrust. If a pilot wants to overpower this movement they can. They're designed to! Just like you might override the cruise control in your car by pressing a little harder than it wants when approaching a hill, a pilot can physically override the auto throttles.

From the information released by the NTSB to date, no effort was made to overpower the auto-throttles during the approach. The first reported effort made to increase thrust occurred at 1.5 seconds prior to impact when the decision to go-round was made. Far, far too late.

CJ