Vref....Interpretation

[bezerker]

I mention the V2 / Vref thing, because on some aircraft there is not really any correlation (although our SOP's have us fly as though there is).

Like the ATR mentioned (and I'm sure it is the same for most multi flap position aircraft) full flap Vref is higher than V2 with flap in the max takeoff flap config (which is what we set for go around after max power is selected). However throughout the weight range, there is no correlation between the speeds (such as add 10 kts to Vref for go around and it will equal V2). Our SOP's call for ref +20 kts then accelerate to Vfs at safe alt and retract remaining slat/flap.

The ref +20 is above the V2 at max takeoff flap for all landing weights, and it is an easier reference to use instead of also figuring out V2 for approach, since we have already figured out Vac and also because all engine climb with flaps at typical landing weights gives ridiculously high climb rates no matter what speed you are at.

xsbank, your career progression is enviable. You must have absolutely enormous travel bags. I don't believe that all your aircraft follow Fougapilot's formula of adding no correction for no reported wind.

I do note that all your lovely aircraft have autothrottles (optional on the 604 I know). And all your aircraft also have modern, accurate avionics. Inertial speed tapes from accurate Air Data and AHRS along with autothrottles, are slightly different than a crusty Collins 80 set up with pitot tubes that have been used as steps to wipe bugs off the windshield one too many times (less potential for error and much improved speed control with newer systems), but I still think the rules are the same.

On most fancy jet planes the speed for approach is calculated by the FMS from the aircraft’s weight, which provides a basic Vref to which a factor for wind must be added. As discussed, this allows for the effect of the wind expected on the approach and is able to account for gusts. Vref + 5 kt is automatically generated by the FMS and this is the speed on the approach to which the autothrottle will control (or the pf will target) unless the speed is modified by the crew.

This is the ususal garbage in - garbage out. The manufacturers choose to add 5 kts for no winds instead of the 10 kts I said, but the a/t's are more accurate and attentive than I am and also they do have a + or - 5 kts built in, so no wind Vref +10 would not be unusual to see over the fence for aircraft with this system. Let me know if your aircraft uses a different method or if it doesn't add any correction by default.

I obviously can't profess to be an expert on landing all aircraft, and we each should follow our AFM's, but we might just be arguing po-tay-toes and po-tah-toes when it comes to reducing power in for touchdown.

The most common technique I have seen used by far is a slight reduction of power over the fence and then a reduction to idle at 20-30'. I already said in a previos post where I have derived this technique from, but I have also seen it built in to the autothrottle logic of many larger aircraft. The 737's I've jumpseated in with a/t seem to reduce to idle at 30'. The Airbuses I've jumpseated in seem to call 'retard' at 30' (or at least don't reach idle power until well below 50'). The DC-10 (long time ago) seemed to reduce a bit of power in the flare and then reduce to idle at 20-30'. Maybe some guys with a/t experience would care to comment on my interpretation errors as well as the logic built into these systems.

I think a sloooow reduction to idle from 50' from a wind corrected Vref is fine. It is the idea of flying an approach with an uncorrected Vref and then quickly chopping the power to idle at 50' that I think carries unessessary risk.

In reality, I guess it is whatever works for your aircraft, I don't proclaim that the techniques used to land the worlds largest jumbo jet should be modified as per my demands, and vice versa. Just as the flare will begin at different heights for different aircraft, maybe power to idle from uncorrected Vref at 50' works well for some, so go ahead. It wouldn't consistantly work well or provide any benefit on the aircraft I have flown.

In any case, I don't honestly believe that manufactures recommend adding no correction to Vref in no wind conditions, and I can't see any downside in carrying speed for unknown winds unless you are planning to land with max brakes and no reverse on an unfactored runway.