Tail wind Vref Corrections

[ranklein]

Does anyone have a good reference for NOT adding any additives for Vref in tailwind? I know one should add only the gust itself, if present.
Any sources, aside from the manufacturers themselves?

Thanks!

[Mach E Avelli]

As Vref itself provides a 30% margin over stall speed, I have always been quite comfortable to fly this speed, with no additives, as a final approach speed when landing in a tailwind. Sometimes I think pilots forget how much 30% of something like 100 knots equates to as a margin when they start adding another 10 or 15 for mum and the kids, then fly another 5 or 10 faster than that anyway.
Although not recommended to take a tailwind into a marginal runway, there are places in the world where the strips are one-way only. Some types e.g. DC3, F27 and that lovely old thing the DH 114, are quite tolerant of even lower approach speeds, down to about 1.2 X stall, and this is what I would fly (did frequently fly) on to short one-way strips with a tailwind in the types mentioned. However, for contemporary transport types, and particularly jets, going below 1.3 Vs on final approach is a no-no because it strays outside the recommended envelope and there are all sorts of monitoring devices that would dob you in, if the F/O didn't. Then again, I hope I don't ever have to fly a jet to the types of strips I mention above!
I believe that an old Boeing manual from the 737-200 era may contain advice to fly only Vref in a tailwind, but can't quote it.

[john_tullamarine]

Consider why you carry approach additives -

(a) steady wind is expected to decrease within the latter stages of the approach and landing. Thus, we expect to see a shear - in the case of a tailwind, a reducing tailwind. There would be no sensible reason to carry an additive in this situation.

(b) a gust pattern, superimposed on the steady wind is unpredictable, so it is desirable to provide for gust events.

There was some discussion on this subject in an old Tech Log thread (http://www.pprune.org/tech-log/10456-737-wind-increment-vref.html). More recent threads have identified the Boeing practice as having been introduced during the early 707 days.

[CaptainSandL]

You don’t add any wind corrections (additives) with a tailwind, but you should still use a minimum of Vref +5kts (Ref 737NG FCTM, Oct 31 2008, Page 1.3). The FCTM now has a good table giving examples of Reported winds, Wind additives & Approach speeds to (hopefully) make it crystal clear.

Some people think that you can approach at Vref+0kt in a tailwind. I think this myth came about from poor wording in early FCTM’s. The earliest copy (B737) I still have is dated FEB 28/90 and reads:
“Do not apply wind correction on final approach speed (VREF) for tailwinds.”

The current FCTM is now more clear about this and reads:
“Do not apply wind corrections for tailwinds. Set command speed at VREF+5 knots (autothrottle engaged or disconnected).

S&L

[john_tullamarine]

Slap on the wrist duly accepted .. what I get for being broadbrush and sloppy with my answers.

.. exits stage left muttering quietly to himself ....

[Mach E Avelli]

Capt Sandl thanks for the update. I will have to amend my wicked, wicked ways. Vref plus 5 it is.

[indiscipline_girl]

Our manual states:

If calm, light and variable, or a tailwind, set VREF +5.

[gimmesumvalium]

Assuming you are flying Boeing the above stands.
But if you are flying Airbus, they have to be contrary:
- if Autothrust is ON, add 5 knots min
- if Autothrust is OFF, add 0 knots!