Simple question regarding Vref and Vref + Factor
- Thread starter surreal1221
- Start date
higney85
Property of Scheduling
Too many to type.
Vref is what well all know is "official". Vref is the number derived to achieve the correct margin over stall in the landing config. I have seen the number anywhere from 1.27Vso to 1.3Vso. All landing numbers are reliant on crossing the threshold at Vref and 50'. Tailwinds, headwinds, and speeds above Vref are given +/- values for landing distance. I'm sure that each a/c is different in what works, but thats why we all eat up different lengths too. I was up front in a -900 that made the exit we make ALL THE TIME in the -200. You would have thought they just figured out how to burn water... different planes perform differently! Common sense prevails!
kellwolf
Piece of Trash
Hitting the TDZ isn't good enough at PCL as far as the FAA is concerned. Any other PCL guys remember the uproar the FAA got in when guys were landing in the TDZ, but NOT within the first 1000-1500 ft of runway? Since then, it's been company mantra to hit the 1000-1500 ft mark. Anything beyond that is outside of company landing standards and should result in a go around. Seriously.
SlumTodd_Millionaire
Most Hated Member
Josh's point is well taken for any CRJ operator. After the TVC overrun at PCL, this became a big issue at ALPA's Safety Department. Flying even a few knots over Vref can lead to big problems on the CRJ with a runway surface that is even slightly slippery, because the numbers are already so inflated to account for the lack of leading edge devices. This is exactly why PCL is now flying everything at Vref all the way down final instead of adding a factor. The airplane will float like crazy, and add in a slippery surface, a 7,000 foot runway becomes awfully short.
higney85
Property of Scheduling
You may recall but I fought that one on the company forum by the horns. I only posted the AIM and FAA literature on the first 3,000 or 1/3rd of the runway. M6 on 18R, P on 36R... Bring it! I'm still rolling to the end on 27 though...... (This is talking about MEM since Kell and I are based here).
Baronman
Well-Known Member
AOPA did a good write-up on the Southwest/Midway accident. They explain some of the performance factors related to that approach and landing. They were actually on-speed but due to many factors weren't able to stop the aircraft. I'm sure it would have been that much worse had they been ten-twenty kts fast.
Baronman
Well-Known Member
No kidding. The CRJ-200 without a doubt has inflated speeds (that's why it's pitched down on final) and you see them float all the time. I'd bet the wing could handle slower speeds but the FAA says "nope." Seems like PNCL realizes this and vref the whole way down makes sense.
surreal1221
Well-Known Member
You tell me. . .BUT. . .
I know that it is possible to make a speed reduction of 5-10kts without bringing the power to idle.
I don't think anyone is making the suggestion to reduce power to idle to make the adjustment from Vref+factor to Vref, rather a simple power reduction to achieve Vref as you cross the 50ft landing screen height.
SlumTodd_Millionaire
Most Hated Member
Airplanes with autothrottles usually take care of the thrust reduction on their own. The 717 pulls the power to idle on its own at about 30 ft RA. No need to even worry about it. The CRJ is obviously very different. I usually started pulling power out just a tad to try to get the 5 knot reduction to arrive at 50 ft at Vref, and then chop the power to idle at the 50 ft RA call. That was when PCL was flying approaches at Vref + factor. Now they're flying everything at Vref anyway.
higney85
Property of Scheduling
Every plane lands different though. On a -200 if you aren't pulling the power back starting at 100ft you will not touch down on the markers, a -700/-900 and you will slam hard. An Airbus calls you a retard starting at 50 ft. The Md-11/10 holds ref to 50 then walks em back all the way to the autobrakes, the diesel 9 keeps the pilots busy all the way through rollout. Moral is this.... Crossing at 50ft and Vref is ideal and planned.
jynxyjoe
Queso King
More evidence CRJ's suck. Failsauce.
Well more learning for me. I'll make sure to continue berating my FO's for not hitting the 1000ft mark in the SAAB and tell them it's for their own good.
surreal1221
Well-Known Member
Of course, not getting into various techniques of managing airspeed in various airframes.
Crossing the 50ft screen height at Vref is what the landing data (unless otherwise noted) requires to be accurate.
granlistillo
Well-Known Member
Excellent points. I would add though that in my experience, if you are on speed, on glideslope and power comes back at 50 ft. You can fly the approach at vref + additive and not float if you dont try to grease it in. On a short runway, you can allow it to settle with an acceptable sink rate without jarring anybody. Sometimes perfect is the enemy of good enough. A greaser followed by smoking the brakes is kinda nonsensical.
kellwolf
Piece of Trash
Oh yeah, and I agree with you. But since there's like one SENTENCE in our books that mentions the 1000-1500 ft thing, well, ya know. The horse has been beaten to a bloody pulp at this point.
And yeah, I have put it down on the 1500 ft markers and rolled to the end of 27 before. Took a LOOOOONG time, but I knew I was gonna do it, so no brakes or TRs for that one. But honestly, I might as well be based in DTW at this point. I haven't flown a MEM trip in like a month and a half.
granlistillo
Well-Known Member
Not saying you are wrong at all. Vref additive during gusting conditions far outweighs other considerations normally. There are some nuances involved. Unless you are at absolute landing minimums, the 200 being a lawn dart you can push the nose down a little bit to start the round out prior to the aim point markers.The 1000 footers are maybe more critical when you get big aeroplanes with the main gear bogies back more than 150 feet from the cockpit.
Better vref + 5 than vref -5 imho
surreal1221
Well-Known Member
Recall that my initial question, and the one I still hold in my mind, is in regards to a no crosswind/gust condition.
Vref+5 vs. Vref-5 could be debatable considering that Vref itself provides either 1.23 to even 1.3 times Vso stall margin. I'll take the difference of 1.27 x Vso for the -200, if someone has the actual that'd be great.
Vref of 142 (at MLW for a CRJ-200) comes from a Vso of 112kts (112 x 1.27 = 142.24kts). Quite the stall margin - even at Vref minus 5 (137kts).
So long as a pilot is making an effort to MAINTAIN Vref I don't see why any self-respecting professional would allow such airspeed decay prior to crossing the 50ft screen height.
Vref+5 vs. Vref-5 could be debatable considering that Vref itself provides either 1.23 to even 1.3 times Vso stall margin. I'll take the difference of 1.27 x Vso for the -200, if someone has the actual that'd be great.
Vref of 142 (at MLW for a CRJ-200) comes from a Vso of 112kts (112 x 1.27 = 142.24kts). Quite the stall margin - even at Vref minus 5 (137kts).
So long as a pilot is making an effort to MAINTAIN Vref I don't see why any self-respecting professional would allow such airspeed decay prior to crossing the 50ft screen height.
higney85
Property of Scheduling
surreal1221
Well-Known Member
What do PTS have to do with this? 
Oh I think I get it. . .if a pilot can satisfy checkride requirements, surely they wouldn't allow airspeed to decay below Vref minus 5kts.
Is that it?
Or. . .Since most companies recommend Vref+5, the ATP standards of +/- 5kts would, on the minus side of things, allow the speed to still be at Vref if the pilot was flying to ATP standards.
Is that it?
Oh I think I get it. . .if a pilot can satisfy checkride requirements, surely they wouldn't allow airspeed to decay below Vref minus 5kts.
Is that it?
Or. . .Since most companies recommend Vref+5, the ATP standards of +/- 5kts would, on the minus side of things, allow the speed to still be at Vref if the pilot was flying to ATP standards.
Is that it?
SpiraMirabilis
Possible Subversive
I like to keep a couple of knots higher than ref even over the fence because I know how inaccurate weight/CG cards are even in ideal situations, so it can't hurt.
The whole discussion is predicated upon being able to accurately identify your ref speed to within a knot or two when I am far from certain that is possible with the tools available. Even when the FMS does it for you it is still can't be that accurate, as it is only doing the speed card math for you.
Edit: Although I do have a different perspective. I fly an airplane that doesn't really float and even if you never touch the brakes can stop in like 2000ft so runway overruns are not as big a concern to me, even for 5000ft runways.
The whole discussion is predicated upon being able to accurately identify your ref speed to within a knot or two when I am far from certain that is possible with the tools available. Even when the FMS does it for you it is still can't be that accurate, as it is only doing the speed card math for you.
Edit: Although I do have a different perspective. I fly an airplane that doesn't really float and even if you never touch the brakes can stop in like 2000ft so runway overruns are not as big a concern to me, even for 5000ft runways.
CaptBill
Well-Known Member
Remember guys that Vref is calculated on a given weight. I absolutely guarantee that the airplane does not weigh exactly what the Vref numbers are predicated on. On a 737-900 with 170 people onboard I would guess the actual weight of the airplane could be off by several thousand pounds either way based on the actual weight of your passengers and cargo. For those of you who do not know, airlines calculate average weights for passengers and bags. If you happen to be flying a bunch of skinny people, your actual weight may be far less than the weight your performance is based on; conversely, if you are carrying a bunch of sumo wrestlers, your actual weight might be thousands of pounds heavier than the weight you are using to determine Vref. That would explain why a particular aircraft might fly great at Vref one day and feel sluggish and a bit slow on another day. I will take my Vref +5 as a little insurance for how fat America has become. Just my 2 cents.....