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11 Answers

V speed

Asked by: 8965 views Commercial Pilot, FAA Regulations, Instrument Rating, Private Pilot

Whats the difference between Vfe vs Vfo?

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11 Answers



  1. Mark Kolber on May 21, 2018

    The answers are available in various publications, including the AFM (pasted below) and in the POH for an airplane which has a differentiation between the two. It’s “extended” vs “operating.” You will find the same distinction in landing gear speeds.

    VFE – The maximum speed with the flaps extended. The upper limit of the white arc.
    VFO – The maximum speed that the flaps can be extended or retracted.

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  2. KDS on May 21, 2018

    Unfortunately, due to the uncorrected software issue with the site, what Mark pasted doesn’t show up (at least not on my computer).

    Also, not to beat a subject to death, but some airplanes have different Vfo speeds for extend and retract. Same thing with gear.

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  3. Kris Kortokrax on May 21, 2018

    I have to admit that you have piqued my curiosity. Vfe is established for structural reasons.

    Vfo is not defined in Part 1 (as Vlo is). I also see no reference to Vfo in Part 23 or 25 certification regulations.

    From a practical standpoint, if Vfo (if it exists) were higher than Vfe, how would one handle the flaps?

    If Vfo were lower than Vfe, would you first slow to Vfo and then be able to speed up to Vfe, and during a go-around need to slow to Vlo to raise flaps during the go-around procedure?

    Is there an example of a POH or AFM which lists a Vfo speed?

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  4. Mark Kolber on May 21, 2018

    Kris, not in any of the 30 or so singles I’m kind of familiar with. Closest POH reference I’m aware of is the A36 Bonanza where, although designated VFE (because there’s only one), it is described as “Do not extend flaps or operate with flaps extended above this speed.”

    Just a guess, but where an airplane has it as a limitation, I would expect it to work like VLO and VLE, where VLO is generally slower than VLE. On the go-around, you retract the gear by VLO (which, may have different speeds for extension than for retarction) . If you don’t, you leave it alone until you have a chance to slow down.

    KDS, you don’t see:

    VFE – The maximum speed with the flaps extended. The upper limit of the white arc.
    VFO – The maximum speed that the flaps can be extended or retracted.

    ?. That’s the pasted text. It’s also the only time I’m aware of the term is used in an FAA publication.

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  5. Mark Kolber on May 21, 2018

    Kris – got one (Google is our friend 😉 )

    The CRJ200 has published VFO as well as VFE. From the manual (Let’s see if this comes out right):

    Flap Speeds
    VFO Maximum flaps operating speed – The maximum speed at which the
    wing flaps can be safely extended or retracted
    • Flaps 0 to 8 degrees: 200 KlAS
    • Flaps 8 to 20 degrees: 200 KlAS
    • Flaps 20 to 30 degrees: 185 KIAS
    • Flaps 30 to 45 degrees: 170 KlAS

    VFE Maximum flaps extended speed – The maximum speed with the wing
    flaps in a prescribed extended position
    • Flaps to 8 degrees: 215 KlAS
    • Flaps to 20 degrees: 215 KlAS
    • Flaps to 30 degrees: 185 KIAS
    • Flaps to 45 degrees: 170 KlAS

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  6. KDS on May 21, 2018

    Mark,

    Sorry. Yes, I do see that. I was thinking there was something lower than that you had pasted.

    Thanks,

    KDS

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  7. Kris Kortokrax on May 22, 2018

    Mark,

    I’m pretty sure that I found the same info that you referenced. It is contained in a POH specific to Chautauqua Airlines. The FAA approval on LEP-1 through LEP-12 is signed off by their Principal Inspector. This appears to be a POH that they have tailored for their operation. The CRJ200 is actually a Bombardier (formerly Canadair) CL-600-2B19. It is shown on TCDS A21EA. In the TCDS, it lists Vfe speeds of 230, 230, 196 & 191 knots respectively for 8, 20, 30 & 45 degrees. It does not list any Vfo speeds. As these Vfe numbers are higher than those in Chautauqua’s version of the POH, there would be no conflict. They can certainly be more restrictive. However, I don’t understand why they would specify the flap operating speeds. As I said earlier, if they were at 215 knots with 20 degrees of flaps extended, they would need to slow to 200 knots to retract them. If just doesn’t make any sense, especially when the TCDS gives a Vfe of 230 for 20 degrees.

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  8. John D Collins on May 22, 2018

    it could in concept be that the actuator has a limitation, but the structure does not.

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  9. Mark Kolber on May 22, 2018

    Kris, sice I’,m not an aircraft manufacurer and never built one, I don’t know. I’d guess the aswer is, the exact same reason some POH specify both VLO and VLE.

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  10. KDS on May 22, 2018

    It can be for a couple reasons. It could be for the actuator. Think of it like this. How hard would an electric motor have to push to get the flaps down at a speed? Does it exceed the limits of the motor?

    With gear, there can be mechanical locks that hold it in place at speeds above what the gear motor is designed to operate.

    That also explains why on some airplanes, Vfe-extend and Vfe-retract are different. Does the motor have to fight against the wind or not. The same logic applies to the gear.

    Somewhere way back in the dusty part of my brain I remember one aircraft where they said you really could lower the gear above Vlo and below Vle without doing any damage except that there was a risk of losing the gear doors. It was one of those “in an emergency, you may want to do this” pieces of information.

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  11. Matthew Waugh on May 26, 2018

    The 200 has a problem with the flaps that required a check on every pre-flight for differential flap deployment. There was a fix provided, I assume that most airlines implemented it, but regardless I’m not surprised to see an airline limitation more restrictive than the manufacturer.
    My info is 8+ years old, but we went through various revisions of flap speeds on the 200. It’s also why we parked at the gate with flaps 8 set so you could do the pre-flight check.

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