smartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0 Posted (3 years 1 week 6 days 4 hours ago) and read 8916 times:
In the FCTM for the 737 it states that the minimum command speed setting is VREF + 5 knots. Why is this? I have been told that we should bleed these 5 knots off over the threshold because your landing distance is based on touching down at VREF?
Is this the same for all Boeings/other aircraft makes, I have heard other aircraft like the BAE 146 approach @ VREF and downtown at less than VREF
KAUSpilot From United States of America, joined Jan 2002, 1969 posts, RR: 31
Reply 1, posted (3 years 1 week 6 days 4 hours ago) and read 8900 times:
It's the same in both the EMB-145 and B744. Why? The airplanes were designed to fly the final approach at that speed. Through the course of a normal flare maneuver the 5 knots will usually be bled off just as the aircraft touches down. Flying for extended periods at Vref puts you too close to stick shaker in my opinion. Of course there are also additives for strong winds.
smartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0
Reply 5, posted (3 years 1 week 2 days 6 hours ago) and read 8100 times:
Quoting tdscanuck (Reply 3): Because the autorthrottle certified +/- 5 knots. It's the only way to have the authothrottle and the landing certification standards "get along" (the autothrottle can't put you below Vref).
so because the autothrottle is +/- 5 knots you have to always set +5 so the autothrottle will never go below vref?
A Boeing training pilot would be a good place, if you've got access to one (that's where I got my information). The Boeing Flight Crew Training Manual (737NG) says, for a stabilized approach, "the airplane should be at approach speed. Deviations of +10 knots to – 5 knots are acceptable if the airspeed is trending toward approach speed". Note that, coupled with Vref+5 approach speed, means that following standard procedure should keep you at or above Vref.
The speed portion of the FCTM also says, "When using the autothrottle, position command speed to VREF + 5 knots.
Sufficient wind and gust protection is available with the autothrottle connected 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." That's basically a tacit admission that the autothrottle will hold you to at least VREF when you set commanded speed to VREF+5.
A different portion says, "When using the autothrottle, position command speed to VREF + 5 knots. Sufficient wind and gust protection is available with the autothrottle engaged that no further wind additives are needed."
CosmicCruiser From United States of America, joined Feb 2005, 2263 posts, RR: 15
Reply 9, posted (3 years 1 week 1 day 10 hours ago) and read 7927 times:
We do ref+5 regardless of A/T or not. The FMS defaults to it. EO is ref +10. we ad the wind factor regardless of direction, head, tail, x-wind. I was just thinking it was a "safety pad" so you wouldn't go below ref (1.3 stall) especially at heavy ldg wgts.