Oakape, just read back the FCTM word by word to understand it correctly,
on page 1.12 FCTM October 31,2008 :
When using autothrottle, position command speed to Vref+5 knots.
Sufficient wind and gust protection is available with autothrottle engaged because the autothrottle is designed to adjust thrust rapidly when the airspeed drops below command speed while reducing thrust slowly when the airspeed exceeds command speed. In turbulence, the result is average thrust is higher than necessary to maintain command speed. This result in an average speed exceeding command speed.
Just imagine if you can work like an autothrottle than you can set the command speed to Vref+5kts, am I correct..???
Vref = 1.3 Vstall at actual configuration and you add another 5 kts, you are still far from stalling the airplane, while you still aimming to stall the airplane at very low altitude
(10 to 5 ft AGL)
I asumming, whatever the condition are as long you are landing and set the bug to Vref+5
(consider head wind correction only) and you fly the entire approach with your corrected speed
(head wind) you are in safe side as the :
"This result in an average speed exceeding command speed"
then you :
"bled off this speed as the airplane approaches touchdown".
even the FMC Approach page give you and +5kts as default.
correct me for my low understanding and poor english, thank you
