Moderators: richierich, ua900, PanAm_DC10, hOMSaR

phllax
Topic Author
Posts: 588
Joined: Wed Jan 11, 2006 6:53 am

### V Ref Speed Question

Hello,

Is it possible in a STOL or any commercial airplane for V1 to be after Vr and V2 if the runway is long enough and the headwind component is strong enough? One would think it could be possible on DEN's 34L, which is 16,000 feet long?

Also, for the pro's out there, if coming in to land do you ever bump the landing Vref speed by 5-10 knots to give you a cushion knowing there may be gusty or windshear conditions on final, so that it's one less thing to deal with at such a critical phase of flight?

JustAnFO
Posts: 31
Joined: Tue Jul 10, 2012 5:47 pm

### Re: V Ref Speed Question

#1 No. FAR certification regs say that V1 must always be less than or equal to Vr.

#2 Yes, though generally at an airline, it's not a "technique", but a defined procedure for calculating Vtarget. It varies with type and operator policies.

Sent from my iPhone using Tapatalk

GalaxyFlyer
Posts: 5631
Joined: Fri Jan 01, 2016 4:44 am

### Re: V Ref Speed Question

By definition, V1 can not exceed Vr; however, refusal speed (accelerate-stop) may exceed Vr but it’s not used as a performance number as you’d be airborne. There are times for unbalanced field length calculation that you need to know the refusal speed.

zeke
Posts: 14979
Joined: Thu Dec 14, 2006 1:42 pm

### Re: V Ref Speed Question

phllax wrote:
Hello,

Is it possible in a STOL or any commercial airplane for V1 to be after Vr and V2 if the runway is long enough and the headwind component is strong enough? One would think it could be possible on DEN's 34L, which is 16,000 feet long?

Also, for the pro's out there, if coming in to land do you ever bump the landing Vref speed by 5-10 knots to give you a cushion knowing there may be gusty or windshear conditions on final, so that it's one less thing to deal with at such a critical phase of flight?

It is possible for V1 to be technically after Vr, however to meet regulatory requirements for Vr to be >= V1 they will increase those speeds. The performance charts or software will make reference to that relationship when generating the speeds.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News

Starlionblue
Posts: 19937
Joined: Fri Feb 27, 2004 9:54 pm

### Re: V Ref Speed Question

To add to the increase in Vref (Vapp on Airbus) in gusty conditions, this is also tied in to autothrust. It takes a moment for autothrust to react to a speed excursion. Having a 3-5 knot buffer means if you have a downward speed excursion by the time you are down to "actual" Vapp, autothrust has reacted already.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo

mmo
Posts: 2054
Joined: Thu Apr 18, 2013 3:04 pm

### Re: V Ref Speed Question

Starlionblue wrote:
To add to the increase in Vref (Vapp on Airbus) in gusty conditions, this is also tied in to autothrust. It takes a moment for autothrust to react to a speed excursion. Having a 3-5 knot buffer means if you have a downward speed excursion by the time you are down to "actual" Vapp, autothrust has reacted already.

Just an addition on Boeings if you have the autothrottles engaged there is no need to add the gust component to the Vref speeds. However, the FCTM also advises, as a technique, you also use a reduced landing flap configuration. I flew for SQ on the 744 and their preferred landing flap configuration was Flaps 30, so in this case, landing flaps would be Flaps 25. The reason is with 30, the additional drag makes the aircraft more susceptible to the gusts and the autothrottles will have a tendency to lag. With the reduced drag with 25, the autothrottles can handle the gusts with no problem.
If we weren't all crazy we'd all go insane!

### Who is online

Users browsing this forum: 747classic, Baidu [Spider], Sokes and 22 guests

### Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos