Vref....Interpretation
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medicineman
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Vref....Interpretation
What is your interpretation of Vref?
"If you wish to travel far and fast, travel light. Take off all your envies, jealousies, unforgiveness, selfishness and fears."...
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wallypilot
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From the horse's mouth. (Or ass..you make the call)
Part 23 AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES
Subpart B--Flight Performance
Sec. 23.73
Reference landing approach speed.
(a) For normal, utility, and acrobatic category reciprocating engine-powered airplanes of 6,000 pounds or less maximum weight, the reference landing approach speed, VREF, must not be less than the greater of VMC, determined in Sec. 23.149(b) with the wing flaps in the most extended takeoff position, and 1.3 VSO .
(b) For normal, utility, and acrobatic category reciprocating engine-powered airplanes of more than 6,000 pounds maximum weight, and turbine engine-powered airplanes in the normal, utility, and acrobatic category, the reference landing approach speed, VREF, must not be less than the greater of VMC, determined in Sec. 23.149(c), and 1.3 VSO .
(c) For commuter category airplanes, the reference landing approach speed, VREF, must not be less than the greater of 1.05 VMC, determined in Sec. 23.149(c), and 1.3 .
Amdt. 23-50, Eff. 03/11/96
Federal Aviation Regulation
Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
Subpart B--Flight Performance
Sec. 25.125
Landing.
(a) The horizontal distance necessary to land and to come to a complete stop (or to a speed of approximately 3 knots for water landings) from a point 50 feet above the landing surface must be determined (for standard temperatures, at each weight, altitude, and wind within the operational limits established by the applicant for the airplane) as follows:
(1) The airplane must be in the landing configuration.
[(2) A stabilized approach, with a calibrated airspeed of VREF, must be maintained down to the 50 foot height.
VREF may not be less than
(i) 1.23 VSRO;
(ii) VMCL established under Sec. 25.149(f);and
(iii) A speed that provides the maneuvering capability specified in Sec. 25.143(g).]
(3) Changes in configuration, power or thrust, and speed, must be made in accordance with the established procedures for service operation.
(4) The landing must be made without excessive vertical acceleration, tendency to bounce, nose over, ground loop, porpoise, or water loop.
(5) The landings may not require exceptional piloting skill or alertness.
(b) For landplanes and amphibians, the landing distance on land must be determined on a level, smooth, dry, hard-surfaced runway. In addition--
(1) The pressures on the wheel braking systems may not exceed those specified by the brake manufacturer;
(2) The brakes may not be used so as to cause excessive wear of brakes or tires; and
(3) Means other than wheel brakes may be used if that means--
(i) Is safe and reliable;
(ii) Is used so that consistent results can be expected in service; and
(iii) Is such that exceptional skill is not required to control the airplane.
(c) For seaplanes and amphibians, the landing distance on water must be determined on smooth water.
(d) For skiplanes, the landing distance on snow must be determined on smooth, dry, snow.
(e) The landing distance data must include correction factors for not more than 50 percent of the nominal wind components along the landing path opposite to the direction of landing, and not less than 150 percent of the nominal wind components along the landing path in the direction of landing.
(f) If any device is used that depends on the operation of any engine, and if the landing distance would be noticeably increased when a landing is made with that engine inoperative, the landing distance must be determined with that engine inoperative unless the use of compensating means will result in a landing distance not more than that with each engine operating.
Amdt. 25-108, Eff. 12/26/2002
Last edited by CID on Wed Mar 07, 2007 4:04 pm, edited 1 time in total.
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fougapilot
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Bandit,
Simple. Their weight changes so little that Vso is not affected by it.
My 601 could land at wheight ranging from 29 000lbs to 45 000lbs (before some one nails me for it, I agree the Max Landing Weight is 36 000lbs, but one can still land heavier in case of emergency. The AFM does list Vref for weights up to 45 000lbs) but you can imagine that our stall speed will not be the same at the higher weight then at the lower ones. Hence the need for a Vref chart.
Most FAR 23 (read less then 12 500lbs here) are not affected by this then do not need to publish such a chart. One approach speed covers the 1.3Vso requirement for all weights.
Cheers,
F
Simple. Their weight changes so little that Vso is not affected by it.
My 601 could land at wheight ranging from 29 000lbs to 45 000lbs (before some one nails me for it, I agree the Max Landing Weight is 36 000lbs, but one can still land heavier in case of emergency. The AFM does list Vref for weights up to 45 000lbs) but you can imagine that our stall speed will not be the same at the higher weight then at the lower ones. Hence the need for a Vref chart.
Most FAR 23 (read less then 12 500lbs here) are not affected by this then do not need to publish such a chart. One approach speed covers the 1.3Vso requirement for all weights.
Cheers,
F
"A stabilized approach, with a calibrated airspeed of VREF, must be maintained down to the 50 foot height"
All the jet aircraft I am familiar with (well, two) we add 5 or more knots to VREF on the approach until short final then we go to VREF. Sounds like we're doing it all wrong. Fouga, do you hold VREF from GS intercept?
All the jet aircraft I am familiar with (well, two) we add 5 or more knots to VREF on the approach until short final then we go to VREF. Sounds like we're doing it all wrong. Fouga, do you hold VREF from GS intercept?
"What's it doing now?"
"Fly low and slow and throttle back in the turns."
"Fly low and slow and throttle back in the turns."
I agree with adding speed to Vref until landing is assured. Here's what I taught on the Seminole in smooth conditions with light winds..
Base, initial final: Vref + 20 (95kts)
Final: Vref + 10 (85kts)
Landing assured/over the fence: Vref (75kts)
5kts was added to the above in moderate turbulence and/or moderate winds.
Base, initial final: Vref + 20 (95kts)
Final: Vref + 10 (85kts)
Landing assured/over the fence: Vref (75kts)
5kts was added to the above in moderate turbulence and/or moderate winds.
Last edited by C-GPFG on Thu Mar 08, 2007 5:54 am, edited 1 time in total.
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fougapilot
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Xsbank,
No we dont. In a perfect world I guess one could, but since our world is imperfect...
Most of the approach are conducted, as I am sure you know, at a speed to meet ATC requirement up to the FAF. Just today in YYZ ATC had us crossing the FAF at 190kts. The CL (recommendation on the 601, limitation on the 604) must be approached at Vref + wind correction (50% of the steady wing plus all of the gust up to a maximum of 20kts). However, in a no wind condition, I have absolutely no problem flying down the approach exactly at Vref. Many CL pilot like to carry a few knots "for mom and the kids", but I for one do not believe in this practice.
The "a stabilized approach, with CAS of Vref, must be maintained down to the 50' height" is only for certification. Basically, it explain to you and I the condition that have to be met for the airplane to perform exactly according to the book. I saw this on a weekly basis back when I was teaching at FSI; many pilots refused to apply the specific technique of the AFM (max power before brake release for take off or maximum brake application for landing) but still insisted on taking off or landing on short runway because the book said the airplane could do it.
In reality one can fly the approach at any speed one desire as long as it is not below Vref. But if one's very survival depends on landing in the exact distance listed in the book, one better fly the approach exactly as per the book which includes (for most jet) crossing the treshold at 50', with engines at idle and at Vref.
Cheers,
F
No we dont. In a perfect world I guess one could, but since our world is imperfect...
Most of the approach are conducted, as I am sure you know, at a speed to meet ATC requirement up to the FAF. Just today in YYZ ATC had us crossing the FAF at 190kts. The CL (recommendation on the 601, limitation on the 604) must be approached at Vref + wind correction (50% of the steady wing plus all of the gust up to a maximum of 20kts). However, in a no wind condition, I have absolutely no problem flying down the approach exactly at Vref. Many CL pilot like to carry a few knots "for mom and the kids", but I for one do not believe in this practice.
The "a stabilized approach, with CAS of Vref, must be maintained down to the 50' height" is only for certification. Basically, it explain to you and I the condition that have to be met for the airplane to perform exactly according to the book. I saw this on a weekly basis back when I was teaching at FSI; many pilots refused to apply the specific technique of the AFM (max power before brake release for take off or maximum brake application for landing) but still insisted on taking off or landing on short runway because the book said the airplane could do it.
In reality one can fly the approach at any speed one desire as long as it is not below Vref. But if one's very survival depends on landing in the exact distance listed in the book, one better fly the approach exactly as per the book which includes (for most jet) crossing the treshold at 50', with engines at idle and at Vref.
Cheers,
F
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fougapilot
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C-GPFG
I agree with your practice, but must point out a difference between fying FAR 23 and FAR 25 airplanes (below 12500 vs above 12500).
A lot (if not most) small twin have a published Vy that is somewhat higher then approved approach speed. Back when I was fying Aztecs, we regularly flew out of a 1500ft strip. We would fly the complete approach above Vy and when we were on short final we would slow down to somewhere near Vmca as to minimize landing distance.
A lot (if not most) larger airplane have a Vref that is quite higher then Vmca. For the 601, the Vmca is 116kias and the minimum Vref is 123kias with most landings are done with a Vref of 128-132kias. These airplanes do not have a published Vy speed. Should one need to climb single engine one must fly V2 (20% above stall speed for the specific configuration) all these numbers are available directly from either the checklist, stored in the EFIS or like in the 604 computed on each approach by the FMS.
So I guess my point is that when flying a larger airplane at its minimum approach speed we are still above Vmca and Va. While in a smaller twin when flying at the minimum approach speed you could be below both Vmca and Vy.
Cheers,
F
I agree with your practice, but must point out a difference between fying FAR 23 and FAR 25 airplanes (below 12500 vs above 12500).
A lot (if not most) small twin have a published Vy that is somewhat higher then approved approach speed. Back when I was fying Aztecs, we regularly flew out of a 1500ft strip. We would fly the complete approach above Vy and when we were on short final we would slow down to somewhere near Vmca as to minimize landing distance.
A lot (if not most) larger airplane have a Vref that is quite higher then Vmca. For the 601, the Vmca is 116kias and the minimum Vref is 123kias with most landings are done with a Vref of 128-132kias. These airplanes do not have a published Vy speed. Should one need to climb single engine one must fly V2 (20% above stall speed for the specific configuration) all these numbers are available directly from either the checklist, stored in the EFIS or like in the 604 computed on each approach by the FMS.
So I guess my point is that when flying a larger airplane at its minimum approach speed we are still above Vmca and Va. While in a smaller twin when flying at the minimum approach speed you could be below both Vmca and Vy.
Cheers,
F
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co-joe
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Interesting question really. One of the guys I fly with seems to think that Vref is actually your touch down speed. Boy he has some hard landings! 
I always thought of it as your "over the fence speed" and I usually touch down at more like Vref minus 10 to 15 (when the rubber actually touches the pavement). To fly it on AT ref you land flat (almost wheel barrow like) and really have to drive it on cause if you flare at all...you balloon.
The 50' number sounds right to me but I can't remember where I learned that particular "cat skinning" technique.
I always thought of it as your "over the fence speed" and I usually touch down at more like Vref minus 10 to 15 (when the rubber actually touches the pavement). To fly it on AT ref you land flat (almost wheel barrow like) and really have to drive it on cause if you flare at all...you balloon.
The 50' number sounds right to me but I can't remember where I learned that particular "cat skinning" technique.
Fouga, I had forgotten VREF + the wind correction - that's what my brain cells were groping for when I was asking you for corroboration. Thanks for that.
How long were you at FSI? You can pm me if you prefer.
How long were you at FSI? You can pm me if you prefer.
"What's it doing now?"
"Fly low and slow and throttle back in the turns."
"Fly low and slow and throttle back in the turns."
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fougapilot
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Fougapilot's posts are right on. Having extra speed above Vref should be done for a reason: Residual ice, winds, turbulence, other. Even "my airspeed control is poor" would be a better reason than mom and the kids. See today's Garuda crash. http://www.telegraph.co.uk/news/main.jh ... rash08.xml
I don't know about the rest of the turboprop fleet but i have run across many King Air drivers who think that you should only slow to Vref short final. This is compounded by older King Airs having both Vapp and Vref speeds published in the checklist.
Once you are in the landing configuration (gear down, flap full), the speed to fly is Vref + specific extras.
I don't know about the rest of the turboprop fleet but i have run across many King Air drivers who think that you should only slow to Vref short final. This is compounded by older King Airs having both Vapp and Vref speeds published in the checklist.
Once you are in the landing configuration (gear down, flap full), the speed to fly is Vref + specific extras.
uh, generally it's ATC - you wanna take a little airplane to a big airport?Having extra speed above Vref should be done for a reason
A really fun approach in the Pitts (preferred by Tucker, Leroy, Stewart, Cabanas) is wide open throttle, which results in 180 to 200 mph.
Then, very short final, throttle all the way back, the 3 prop blades go fine, the de-celeration is quite impressive. If you time it right, you touch down level at 120 mph on the mains. Stick forward to keep the tail up during the rollout.
ATC is usually pretty happy when I keep it over 180 mph.
Someone else here was talking about flying an ILS in a 172 at 75 knots IAS with a 15 knot headwind. I'm sure he's really popular in the tower.
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It's the Pitts
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In my company we fly Navajos into shorter strips. On a longer paved strip we use a Vref of 100 and on the shorter gravel strips we use a Vref 95. I find that by using a Vref of 100 you use a lot more runway. The 5 extra knots alow you to float down the runway. Flying in Canada floating down the runway 1000 ft could be the difference between stopping and overunning.
You got the Nod for the Sod
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snaproll20
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I disagree with flying exactly at Vref from FAF (or from where ever on final) with no winds or light winds on the field.
There is very seldom 'no' wind. There will almost always be a few knots on the ground, gusting to at least a knot or two above that, although it won't be reported if it is less than 5 or something. Can you say for certain that the wind at 1000' is the same or less than that on the ground? Isn't the rule of thumb is that the wind doubles at 1000 agl? So with zero wind reported, it could easily be 4 gusting to 6 kts, but it is reported as calm or light and variable. So at 1000 ft it could easily be 8 gusting to 12 knots, or more. According to the Vref formula, add half the wind and all the gust, so in this case 4 + 4 = 8 knots. I would just add 10 kts to ref as a minimum or under zero wind conditions. Because you just don't know what the winds are at 1000' or 2000'.
Why is it important to add this speed anyway? Because there is the potential for decreased performance windshear on descent and you are covering your ass at the crummy end of the speed zone.
So my ASI say we are ref -5 but my buddies says he is at ref, who am I to argue? So he gets a few knots slower, and just as I am about to call for an airspeed correction, we get a little gust dropping the airspeed about 10 knots (and don't tell me you've never seen that), just at my partner is pulling on the yolk a bit to correct for glidslope, and he is also in a slight bank to correct for centerline. Is that the stall warning or the coffee pot empty buzzer? In 10 seconds it won't matter anyway.
Adding a 10 kt min to ref will hopefully ensure that ugly situation doesn't happen.
Newer quick response jet engines, straight wings on jets, and turboprops that blow air over the wind are less succeptable to the inertia problems that can come up.
What about the increased landing distance due to the added speed?
Well, there is a huge margin of safety with jet aircraft (you have to land in 60% of available distance). If 10 kts adds 40% to your landing distance, I will give you a paycheck. If you are landing without factored distance (private operator) and are landing at a field that is pretty much exacty what your charts say your landing distance is, well, you are taking a risk under any wind conditions in my opinion. In any case, a 10 kt increase in ref should only add a few knots to your touchdown speed, and in reality, most of the deacceleration comes after the wheels are on the ground, and + or - 10 kts shouldn't affect your touchdown point by much.
I know some pilots don't add a correction to ref until really windy conditions or will slow to uncorrected Vref the last few hundred feet because they say the landing charts are affected.
Do you actually use the headwind component to figure out your landing distance? If you need the headwind in order make the field work, maybe you can look for a longer runway. Use zero wind (or 5 kts as allowed by TC for dispatch) for figuring out your performance and the reduced groundspeed from the headwind will easily cover for the few knots you are adding.
As far as reducing the power to idle at 50', I have never really seen anyone do that in a jet unless they are ref plus 20-30 and have 10,000' ahead of them. The manuals I have don't recommend doing the 50' thing , and it would be one hell of an arrival if the power was cut to idle at 50' and the plane exactly at Vref (although I have only flow older jets and the newer ones may not bleed speed off as quickly, although I assume they do with all the shit hanging out and power at idle). And I know a few months ago there was a discussion on here regarding that technique, but I don't agree with it.
If you are at an airline or a big company with SOP's, follow them. My opinion is if you are new to a jet, for God's sake, add a few knots to ref. Call it for unknown winds, for Grandma, or whatever.
If you are on a King Air or other turbo prop, you really only need to add the gust to the ref, but really, speed control is so easy in these things that you should just brief a speed and stick to it Vapp or Vref or Vref + 20 or whatever. I'm not saying it's the best technique, but anyone who can't bring a King Air to a stop in under 3000' when crossing the fence at ref +20, needs remedial training.
Flame away.
There is very seldom 'no' wind. There will almost always be a few knots on the ground, gusting to at least a knot or two above that, although it won't be reported if it is less than 5 or something. Can you say for certain that the wind at 1000' is the same or less than that on the ground? Isn't the rule of thumb is that the wind doubles at 1000 agl? So with zero wind reported, it could easily be 4 gusting to 6 kts, but it is reported as calm or light and variable. So at 1000 ft it could easily be 8 gusting to 12 knots, or more. According to the Vref formula, add half the wind and all the gust, so in this case 4 + 4 = 8 knots. I would just add 10 kts to ref as a minimum or under zero wind conditions. Because you just don't know what the winds are at 1000' or 2000'.
Why is it important to add this speed anyway? Because there is the potential for decreased performance windshear on descent and you are covering your ass at the crummy end of the speed zone.
So my ASI say we are ref -5 but my buddies says he is at ref, who am I to argue? So he gets a few knots slower, and just as I am about to call for an airspeed correction, we get a little gust dropping the airspeed about 10 knots (and don't tell me you've never seen that), just at my partner is pulling on the yolk a bit to correct for glidslope, and he is also in a slight bank to correct for centerline. Is that the stall warning or the coffee pot empty buzzer? In 10 seconds it won't matter anyway.
Adding a 10 kt min to ref will hopefully ensure that ugly situation doesn't happen.
Newer quick response jet engines, straight wings on jets, and turboprops that blow air over the wind are less succeptable to the inertia problems that can come up.
What about the increased landing distance due to the added speed?
Well, there is a huge margin of safety with jet aircraft (you have to land in 60% of available distance). If 10 kts adds 40% to your landing distance, I will give you a paycheck. If you are landing without factored distance (private operator) and are landing at a field that is pretty much exacty what your charts say your landing distance is, well, you are taking a risk under any wind conditions in my opinion. In any case, a 10 kt increase in ref should only add a few knots to your touchdown speed, and in reality, most of the deacceleration comes after the wheels are on the ground, and + or - 10 kts shouldn't affect your touchdown point by much.
I know some pilots don't add a correction to ref until really windy conditions or will slow to uncorrected Vref the last few hundred feet because they say the landing charts are affected.
Do you actually use the headwind component to figure out your landing distance? If you need the headwind in order make the field work, maybe you can look for a longer runway. Use zero wind (or 5 kts as allowed by TC for dispatch) for figuring out your performance and the reduced groundspeed from the headwind will easily cover for the few knots you are adding.
As far as reducing the power to idle at 50', I have never really seen anyone do that in a jet unless they are ref plus 20-30 and have 10,000' ahead of them. The manuals I have don't recommend doing the 50' thing , and it would be one hell of an arrival if the power was cut to idle at 50' and the plane exactly at Vref (although I have only flow older jets and the newer ones may not bleed speed off as quickly, although I assume they do with all the shit hanging out and power at idle). And I know a few months ago there was a discussion on here regarding that technique, but I don't agree with it.
If you are at an airline or a big company with SOP's, follow them. My opinion is if you are new to a jet, for God's sake, add a few knots to ref. Call it for unknown winds, for Grandma, or whatever.
If you are on a King Air or other turbo prop, you really only need to add the gust to the ref, but really, speed control is so easy in these things that you should just brief a speed and stick to it Vapp or Vref or Vref + 20 or whatever. I'm not saying it's the best technique, but anyone who can't bring a King Air to a stop in under 3000' when crossing the fence at ref +20, needs remedial training.
Flame away.
You're not drunk if you can lie on the floor without holding on
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fougapilot
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Bezerker,
I would really like to know whom cross the fence a Vref + 30kts in a jet. Just want to make sure I won't end up a passenger on their airplanes.
At the end of the day, it's still a free country. Just easier to explain certains techniques to the judge then other.
Cheers,
F
I would really like to know whom cross the fence a Vref + 30kts in a jet. Just want to make sure I won't end up a passenger on their airplanes.
At the end of the day, it's still a free country. Just easier to explain certains techniques to the judge then other.
Cheers,
F
fougapilot,
I didn't say I condoned ref + 30, just that I had seen it, as I'm sure many unfortunately have (but kudos for picking the most extreme point in my post to mention).
So conversely, I would like to know who is at ref with no correction 5 miles back, so that I can avoid flying with them. (not that many of us on here have an option of choosing between multiple chartered jet companies on which we travel in the back with;)
As far as the judge is concerned, (and I don't think I would be talking to one because of reasons mentioed in my previous post), I think I would rather tell him I added 10 kts for an unknown but likely wind component, than to tell him I guessed that there was no wind located 1-2000' above and 3-5 miles away from the last hourly wind report.
It is what FSI, Simuflite, multiple training Captains, and several well known books ('Fly the Wing' comes to mind) have recommended to me and it has worked well so far.
The 601 may be different for some reason.
I didn't say I condoned ref + 30, just that I had seen it, as I'm sure many unfortunately have (but kudos for picking the most extreme point in my post to mention).
So conversely, I would like to know who is at ref with no correction 5 miles back, so that I can avoid flying with them. (not that many of us on here have an option of choosing between multiple chartered jet companies on which we travel in the back with;)
As far as the judge is concerned, (and I don't think I would be talking to one because of reasons mentioed in my previous post), I think I would rather tell him I added 10 kts for an unknown but likely wind component, than to tell him I guessed that there was no wind located 1-2000' above and 3-5 miles away from the last hourly wind report.
It is what FSI, Simuflite, multiple training Captains, and several well known books ('Fly the Wing' comes to mind) have recommended to me and it has worked well so far.
The 601 may be different for some reason.
You're not drunk if you can lie on the floor without holding on
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waterpooch989
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Actually, If you reference "Handling The Big Jets"
You will find that Vref is based on weight and configuration such that in the event of a "Go Around" , the aircraft will achieve V2. For those of you who fly aircraft with published weight cards you will find that Vref has a direct correlation to V2.
V2 in that case would be based on your go-around configuration, for example in the ATR42-320 we ref around 120kts for icing bug, and go around will always be something above this (around 5-6 kts). It's assumed that when you "go around" that you're selecting flaps back to 15...bezerker wrote:V2 based on what flap/slat configuration?
Because of bad instructing. Stop that habit at the first landing a student does. There's not a whole lot of extra floating to be done in the north.bandit1 wrote:I always wondered why small singles like 150's, 172's etc... don't have a Vref chart or table.
Seems like at least 80% of weekend warriors and students are smokin' in way too fast all the time. And floating down half the runway. WTF?
Everything comes in threes....
