Flap Maneuver Speeds

[Guest frankathl]

Why are flap maneuver speeds for the 767(unlike the 737) given as a function of VREF, for example, Vm Flaps 15 = VREF30+20? I assume it is because VREF is dependent on weight, thus the flap maneuver speeds will also vary in proportion to the weight of the aircraft? But, then, how do I "Accelerate and climb at VREF30+80 knots" after takeoff, as instructed in the 767 Flight Manual? How do I derive a VREF value at this stage in the flight? Can I use the FMC Approach Page?BR,Frank

[teropa]

Hi Frank,For real world operations you would simply look at the landing speed charts to get your Vref30 for the planned take-off weight you're having for departure. Then setting the bugs based on that speed. In real life they have nice little speed booklets (or onboard laptop PC's) where they show the basic V-speeds and the Vref30 (plus a million other speeds / things) on the respective weight page.In PIC & LDS you needn't worry about even looking at the approach page (you can, of course!), because the speed-bug option knows to set the speedbugs according to Vref30-based schedule.Tero

[Guest frankathl]

Thank you, Tero. "...Vref30 for the planned take-off weight "I thought VREF referred only to LANDING speed? No? This is where I'm confused."...the speed-bug option knows to set the speedbugs according to Vref30-based schedule."How does it know this(sorry, don't have the LDS 767 yet)?By the way, does the 737NG also use VREF in calculating flap maneuver speeds? The manual makes no reference to VREF, eg Flap 1 @ Vm Flaps 1 Speed Bug.BR,Frank

[teropa]

Frank,1. Vref30 is Vref30 whether you are taking off or landing. Sure, it is used for landing, as it's the reference flap30 landing speed, but it's also the basis for the flap schedule, and thus it's needed for the takeoff part as well. You will not use the Vr (rotate) for flap maneuvering speeds, you'll always use the Vref30, as that's the way Boeing designed it. So, forget what phase of flight we're talking about, Vref30 is what you use for flap schedule.2. The speedbug option is obviously programmed to follow the correct Vref30 schedule, because the panel senses the weight of the aircraft and can thus look up the respective Vref30 for that weight, and thus also set the bugs correctly.3. Sure the NG works on the same principle. The difference is that the NG uses flap40 landing speed (Vref40) as the basis, and the increments are different (as are the flap settings in that bird too). See below for Boeing crew training manual explanation on this:http://pilots.svil.fi/teropa/jako/ng1.jpghttp://pilots.svil.fi/teropa/jako/ng2.jpgTero

[Guest frankathl]

Thanks, Tero, for a very good explanation!BR,Frank