Simple question regarding Vref and Vref + Factor

surreal1221

surreal1221

Well-Known Member
What do you cross the 50ft landing screen height at?

Vref or Vref+additives?

To dumb it down to the lowest common denominator, no crosswind.
 
Your company manual should have it clearly explained. I have always understood 50ft @ref. This is what all the landing numbers are predicated on and this is how the a/c was certified. That being said.... Common sense prevails- If there are gusty winds (+/- 10 knots) and i'm getting knocked around I will typically carry a few extra knots... especially as the green line is jumping all over the place and many times it's above Vref. It's amazing how quickly you can stop when you have 30kts of wind with a 20kt factor in your face.


For your answer- Vref@50ft.
 
Yes, I agree the company manual should have it clearly explained. My kit is at the airport, but my question isn't really in regards to what our respective companies tell us what to do - but - what YOU (general use) are doing out on the line.

I know more than one pilot who thinks you are supposed to cross the 50ft screen height at Vref+factor as opposed to Vref.

This mindset is a leading factor in turbojet overrun incidents, yet is not (IMHO) being emphasized enough in training.
 
I posted Vref, because that was what the guidance in my last aircraft that actually HAD a published Vref said (and that assumes a flaps 50 approach)... But I think the real answer is:

Whatever speed the POH, -1, regulations, operator's manual, etc. says. It probably varies from aircraft to aircraft! I don't think this question has a real answer more than that.
 
So for everyone then. . .

What speed (Vref or Vref+additive factor) is the performance data for landing based off of.

That right there is my ultimate point. So fish, off of that question do you still think the question doesn't have a right answer?

AC 91-79 might also be a good read.
 
I think landing data is based on being at 50' at Vref. Fly the approach at Vref+whatever.

Actually I remember on the type ride this was a pretty big deal. I think PTS for the SE approach was to land within Vref +/-5kts. Well, if your target during the approach is Vref+5, and you were a few knots fast you had to slow below your target by the time you were at 50'.
 
Even when we flew Vref + 5 for approaches, we were still supposed to cross the 50 ft mark at Vref. Now we just fly Vref the whole way down.
 
Depends on what the manufacturer used to determine landing distances. In the might BeechJet it is Vref, throttles AT idle and crossing the runway end at 50'. Now in practice that is not "practical" IMO, too much of a decent rate (airplane is rated for 600 FPM landings) and makes for too rough of a landing, but we are talking, at most, for a nominal airport a 3500 foot cross the runway to full stop using just breaks using the manufactures technique.

So in practice, cross at Vref throttles coming to idle somewhere from 75 feet to 40 feet and still touching down on the 1000 or 1500 foot markers.

Vref+ additive is what I fly from FAF to DH/MDA and start slowing to Vref from MDA/DH to the end of the runway or as needed by visual pattern, etc.
 
What do you mean by "Factor"?

(edit to add: )
I'll go ahead and give an answer even without knowing for sure what you mean by "Factor"

We fly the approach at Vapp and plan on crossing the threshold at Vref. If there are gusty winds, we add 1/2 the gust factor to Vref, which we informally call "adjusted Vref". If winds are 14G20, we add 3 knots to Vref, and aim for that figure when crossing the threshold.
 
I fly Vref +5 to touchdown with winds at 10 knots or less. The 737, specifically the -800s and -900s, have a tendency to have the bottom drop out in the flare flying at Vref. Flying +5 to +10 works well for me and the airplane is so much more controllable. In my opinion, the controllability advantage more than makes up the extra few feet it may take to stop. Many of the old timers I used to fly with flew a minimum of Vref +10. I always view Vref as a minimum speed rather than a recommended speed. Boeing technique is to maintain Vref + additive until threshold crossing then begin reducing speed as you prepare to touchdown.
 
I really hope this discussion is beneficial.

My ultimate point is that considering contaminated runways, the likelihood of having an overrun in a turbojet is greatly increased when maintaining Vref+factor when crossing the landing screen height of 50ft as opposed to Vref.

Advisory Circular 91-79 details some of this stuff. Ultimately, I'd rather have a firm, perhaps rough to the people in the back touchdown on a contaminated runway, while crossing the landing screen height of 50ft at Vref. Rather than the alternative of Vref+factor, landing "smooth" and ending up in the ditch at the far end because I've always landed Vref+factor and out of habit didn't make the sound judgment to make sure I crossed the 50ft screen height at Vref.

Discuss

calcapt said:
I always view Vref as a minimum speed rather than a recommended speed.
Click to expand...

Which is something I've heard many Captains talk about. But, I don't really understand it considering that Vref is a calculated speed based off of 1.23 x Vsro where Vsro is the stall speed in the landing configuration.

So really - minimum speed?

excesspeed.jpg
 
What sort of contaminated runway are you landing on that would be rough?

wet runway = squishy landing
snowy runway = squishy landing
Animal dung covered runway = squishy landing
landmine covered runway = maybe?
 
Rough was an adjective to describe the landing, not to describe the runway surface. Shouldn't have even mentioned it as it appears it is distracting from the real debate/discussion.
 
surreal1221 said:
Rough was an adjective to describe the landing, not to describe the runway surface. Shouldn't have even mentioned it as it appears it is distracting from the real debate/discussion.
Click to expand...

No I think it contributes the discussion just fine. I'm curious who is using speed as a crutch to somehow make a softer landing? I wasn't talking about the surface. If the runway is wet or snow covered it is gonna be a "soft" landing.

Disclaimer: just a turboprop captain. I never even took a jet course so someone is gonna have to explain to me this one.
50' @ Vref unless my book says otherwise.
 
I do try an cross the 50 ft pt at Vref, and I find that if you maintain that speed in the flare by adding power you usually get a pretty good landing without floating.
 
My company's book says this:

Factored landing distance is the landing distance at the planned destination airport required to satisfy FAR 121.195, (i.e., allows a full-stop landing within 60 percent of the available landing distance). Factored landing distance data is based on crossing the beginning of the available landing distance at 50’ at VRF with the flaps in the specified landing configuration.
 
Vref + 5 with no gusts. You don't pull out the power on the 767 until ten feet or bad things happen.
 
Even if you crossed the threshold at Vref + 10 (the highest additive for BBD) you should be able to touch down in the touchdown zone, if not execute a go around. That solves the overrun problems.

A firm landing in the touchdown zone is better than a greaser 4000' down the runway.
 
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