Hi,Could someone explain the concept of Vref and Vref30, please, and how I can determine these speeds for PIC? I need to compute these values in order to set up the flap schedule for takeoff and approach:Flap 15

Frank,I am not sure what you mean by the "concept of Vref.." but generally Vref is the approach speed of the aircraft (wind additions are made to Vref to achieve the target speed or actual speed flown, at least for Boeing products)and is for almost all transport category jet aircraft 1.3 times the 1g stall speed for that weight in the landing configuration. Vref30 refers to the 1.3 speed based on using 30 deg of flap. Other speeds are based on additions to that Vref, such as you have listed.You don't need to compute them since the speeds are available in the FMS and the bugs will be set automatically using the hidden click area on the airspeed indicator. Otherwise, it is simple math to do the additional 20 knot increments.Don't know if that helps or not.Kevin in CYOW

Hi Kevin,I should have said "definition of Vref", which you've given as "1.3 times the 1g stall speed for that weight in the landing configuration"(also applies to Vref30, mutatis mutandis), so thatclears that up! My next question would have been, "How do you find the stall speed for various flap configurations without the a/c manuals?", but,as you say, the FMC will compute the various required speeds and display them on the AI. I should admit that I'm new to PIC(I guess it's obvious, huh? :-)) and didn't remember the significance of the bugged speeds on the AI(gulp!). I've since been doing some searching in the PIC archives, and found additional information on takeoff and approach speeds, including the meaning of the white bugs settings.Thanks for your help,Frank

Vref and Vapp...Hi Kevin,Maybe you can help clear something up for me too...please correct me wherever I may be wrong in my assumtions...Vapp (approach speed) I understand to be the Vref + wind compensation....which I understand to be half of the speed plus the full gust (if any). 1) When 'they' say half of the "speed", does that refer to the actual headwind component of wind direction/speed (assuming a non-tailwind landing), or the total speed of the wind, whether it be a crosswind or otherwise?2) When winds are relatively calm, I have seen suggestions to use Vref + 5kts as a standard safety "cushion". If Vref is the minmum maneuvering speed, does that not already have a built in cushion (1.3 stall speed @ 1g)? In calm winds, my Vref would be my Vapp would it not?3) When using flap 25 for landing, as I mostly do, I have been calculating my Vapp with Vref flap 25 speed in the FMC as the base, is this correct? Maybe if you could show a couple calculations based on the follwing:Assumptions:- B763- CYYZ landing runway 23 (mag hdg 236)- Vref(30) at 115 tons LW is approx 130kts- Vref (25) is approx 134kts (from memory)a) Winds 290 17 gust 34Vapp = vref(25)+ + =Vapp = vref(30)+ + =Target touchdown speed = :( Winds 240 4kts (calm)Vapp = vref(25)+ =Vapp = vref(30)+ =Target touchdown speed = ----------------Vapp being my approach speed, Vref would be my lowest maneuvering speed, my target touchdown speed would be how far below Vref?----------------FYI - what I have been doing is vref(25) + half the -total- contstant wind speed + full gust....seems to me I am approaching too fast in certain conditions, hence the questions...Thanks for the help.Rob.

I can't imagine that this hasn't been covered before in the forum, but I'll try explaining.>1) When 'they' say half of the "speed", does that refer to>the actual headwind component of wind direction/speed>(assuming a non-tailwind landing), or the total speed of the>wind, whether it be a crosswind or otherwise?Technically it's the headwind component, but many pilots/airlines just use the wind speed as long as it's not a tailwind.>2) When winds are relatively calm, I have seen suggestions to>use Vref + 5kts as a standard safety "cushion". If Vref is>the minmum maneuvering speed, does that not already have a>built in cushion (1.3 stall speed @ 1g)? In calm winds, my>Vref would be my Vapp would it not?The minimum Vapp for the 767 is Vref + 5. Don't ask me why. :)>3) When using flap 25 for landing, as I mostly do, I have>been calculating my Vapp with Vref flap 25 speed in the FMC as>the base, is this correct?Correct.The maximum wind/gust addition to Vref is 20 kts, and the minimum addition is 5 kts, so your examples aren't "ideal": In example a) Vapp = Vref + 20, and in example :( Vapp = Vref + 5.I'll change the wind speeds a little to make it more clear. (We'll assume the same weights and Vref speeds.)Example:c) Winds 290 14 gust 19Vapp (flaps 25) = 134 + 7 + 5 = 146 KIASVapp (flaps 30) = 130 + 7 + 5 = 142 KIAS>Vapp being my approach speed, Vref would be my lowest>maneuvering speed, my target touchdown speed would be how far>below Vref?It shouldn't be much, if at all, below Vref. I don't have my manuals here so I can't check exactly what's recommended. If I remember correctly you should keep the wind additives until passing the threshold, and after that not reduce speed to less than Vref + 5.>FYI - what I have been doing is vref(25) + half the -total->contstant wind speed + full gust....seems to me I am>approaching too fast in certain conditions, hence the>questions...That sounds correct, as long as you don't add more than 20 kts to Vref.Martin767 fetishistIt's a lot like life and that's what's appealing

Just to clarify a few particulars below is a passage from the Boeing manual:"If the autothrottle is disengaged, or is planned to be disengaged prior to landing, the recommended method for approach speed correction is to add one half of the reported steady headwind component plus the full gust increment above the steady wind to the reference speed. One half of the reported headwind component can be extimated by using 50% for a direct headwind, 35% for a 45 degree crosswind, zero for a direct corsswind and interpolation in between."Hope this helps.

>Just to clarify a few particulars below is a passage from the>Boeing manual:>>"If the autothrottle is disengaged, or is planned to be>disengaged prior to landing, the recommended method for>approach speed correction is to add one half of the reported>steady headwind component plus the full gust increment above>the steady wind to the reference speed. One half of the>reported headwind component can be extimated by using 50% for>a direct headwind, 35% for a 45 degree crosswind, zero for a>direct corsswind and interpolation in between.">>Hope this helps.And if you don't disengage, it's just VREF+5 all the way down.

>And if you don't disengage, it's just VREF+5 all the way>down.Really? I've been adding wind correction even when I'm using A/T. Have I missed something in the manuals, or might airlines do it differently?I remember reading that when using autoland Vapp is always Vref + 5.Martin767 fetishistIt's a lot like life and that's what's appealing

Martin,Thanks for the detailed explanation (saves me a whole bunch of typing).I'll just add that, yes, in my experience we don't bother to calculate the headwind component, we just use 1/2 the steady wind for the addition then all the gust to a maximum of 20 knots addition.The min 5 knots is to allow for small variances in the wind that may occur even if it is being reported as calm (or so I am told).For Rob (856 at work), just to make sure we are clear on this, your double bug (if you are simulating AC procedures) may be set for the Flap 25 approach speed but the Vref+40 and Vref+80 bugs are based on the Flap 30 Vref (ie Vef30+40 etc).Ideally, landing (touchdown) is made at Vref-5 (but keep all the gust corrections to touchdown, you just bleed off the steady state component from the threshold to touchdown).Kevin in CYOW

Kevin, Martin, et al, thank you...completely clears it up for me.This forum is tops!Rob.

Yes, whenever you keep it on until touchdown it's just VREF+5, which as you said, that would usually only occur during an autoland. This is from the Continental flight manual for the 757/767.Cheers

Hi Kevin, thanks for clarifying the touchdown speeds etc.Can you confirm that Vref + 5 should always be used if using the A/T? Or is this different with different airlines?Martin767 fetishistIt's a lot like life and that's what's appealing

Martin,While I have flown other Boeings (and their recommended procedures for wind correction etc are all the same as far as I can tell - thus I feel confident answering the questions above), I have not flown the 767/757 so I cannot comment specifically on the Vref technique with A/T. I will ask around though and see if I can find an answer for you. Personally, I would think you would still correct as per normal but, hey, you never know.Kevin in CYOW

Well in COA's manual it says the A/T is advanced enough to keep VREF+5 accurately no matter what the wind. Of course it may vary here and there.

Martin,I am unable to speak for other airlines but Air Canada uses VREF plus 1/2 of the steady headwind component plus the gust regardless of autothrottle setting. The wind additive is always a minimum of 5 and normally a maximum of 20.Crossing the threshold the speed is reduced to touch down at the double white bug speed plus the gust additive.Best Regards,