Auto-throttle & Manual flight
Question 1...
With regard to the auto-throttle operation in B737 Classics and also NG.
When hand flying an instrument approach there appears to be conflicting views whether or not the auto-throttle should be turned off and the throttles operated manually - or the auto-throttle left engaged so that it controls to MCP speed while the pilot hand flies.
Boeing published documents avoid the question, meaning that it is up to company policy. Assuming average piloting skills one would assume that most 737 pilots could cope with flying manually with auto throttle off. Flying manually with auto-throttle controlling IAS does sometimes present a problem with trim anticipation as the throttles move to maintain the desired speed.
What is the preferred method and for what technical reasons? Failing a Boeing published policy, does it simply come down to personal preference? Which leads into another point on auto-throttle usage: Final approach with manual throttle Boeing recommend Vref plus wind additives up to max additives of Vref plus 20 knots.
Q2....With auto-throttle engaged Boeing recommend Vref plus five knots as approach speed, bleeding of the additive approaching touch-down. First question is how do you "bleed off" speed to Vref if autothrottle is controlling to Vref plus five?
Q3.... Although Boeing infer (tongue-in-cheek, maybe?) that the auto-throttle system can correct for gusts much faster than a pilot can using manual throttle, some may have doubts about this. A human can shove open a throttle twice as fast as the automatics can. Therefore if conditions are real gusty would you trust the auto-throttle implicity and thus just add plus five knots to Vref on the MCP - or would you trust your own reactions and fly manual throttle with all the extra gust additives thrown in?
Problem being that landing on a short runway (worse if wet) with gust additives held all the way to touch-down, ups the ante when it comes to landing fast and long.
Q4....30 knot headwind component calls for an additive of 15 knots to Vref. (half the HW). Boeing recommend bleeding of the additive to cross the fence at Vref. Assuming a steady wind and no gusts, 15 knots bleed off is a lot - particularly as Boeing state that you will lose only 3-4 knots in the actual flare. At what height, therefore should you commence bleedingoff the 15 knots?
Q5.....Auto-throttle engaged but speed button deselected on final so that system remains armed, but throttles can be moved by hand.
Does the alpha floor protection actuate (throttles begin to open up) when the speed is reduced below actual Vref for flap setting and weight - or does it cause the throttles to move forward if the speed is reduced below the MCP selected speed? Put another way - if MCP speed set 10 knots above calculated Vref then with speed mode deselected at what point will alpha floor protection start pouring on the power?