V1

[Idunno]

'Decision Speed' or 'Action Speed'....discuss.

[john_tullamarine]

Probably neither. Recent thinking appears to be that the decision is made before V1 in that, if you have not already commenced stopping, then you are committed to going. Boeing and Airbus appear to push this attitude strongly.

[mutt]

Morning J_T,

Recent thinking appears to be that the decision is made before V1 in that, if you have not already commenced stopping, then you are committed to going.

Doesnt that make it an action speed? If you have started to do something by V1 then you are committed to going?

Idunno, older aircraft were certified with the engine failure at V1 and a specific response time during which time that aircrafts speeds was constant, this has now changed to having the engine failure 1 sec prior to V1 (Vef), so that the decision to stop is made by V1, the aircraft also accelerates during the time that it takes to transition to a stopping configuration.

Mutt.

[OzExpat]

I agree with John_T. It's more a "committed" speed than an "action" speed. That's why the following expression is so common to international departures from here...

Happiness is V1 at Port Morbid

:D

[LeadSled]

Folks,

For US built aircraft, if one were to look up the various editions of the FAA Flight Test Guides, going right back to SFAR 422B, through the latest amendment to FAR 25, one would find that the major change is how the actual takeoff charts have been constructed, with differing “pads” in different eras.

The one thing that has NOT changed, ( but has never been taught very well to airline pilots) is the actual definition of V1.

It has always been:

“ The speed at which the takeoff must be continued, if the abort has not already been commneced”.

It follows that the failure, whatever it is ( not engine failure speed – don’t confuse this with certification requirements for engine out cases) has to be recognized, and a decision made, and the abort commenced, all before V1.

After some nastiness, some years ago, Delta did a survey of pilots turning up for recurrent training, by far the large majority described V1 as the “engine failure speed”, or “takeoff decision speed “, just as well we have not had too many critical aborts over the years, when the same survey was done in Australia, the results were the same as Delta, more or less.

Result, more educational material, changes to all Boeing manuals, articles in Boeing magazine, and a subject for recurrent training.

Now for another subject of much "debate", again FAA and SFAR 422B through FAR 25, who thinks Vref is 1.3 Vs.

Tootle pip!!

[john_tullamarine]

.. at the end of the day it is only semantics ... on an accel-stop limited runway, the risks are "reasonably" controlled (ignoring surface friction degradation .. lap of the gods stuff that) provided the aircraft, if not ALREADY in stop mode, keeps going at V1. Clearly if the runway has additional margins, then the situation is not so critical .. however, the pilot generally doesn't have the numbers to make an adjustment and the benefits of SOP standardisation are of major importance.

History pretty clearly suggests that the risks in going usually are less than the risks in stopping from the region around V1 ... hence the standard 80/100 kt (according to your preferred flavour) division between routine and only very serious accel-stop manoeuvres.

Vref ... mmmm .... do we really want to get tangled up in that one, Mutt ?

[Idunno]

Thanks for all the comments.
Yes my own understanding of the current definition is that it (V1) is an 'Action Speed'. Certainly my Airbus performance manuals state that absolutely clearly. However when I ask colleagues to define V1 I still get that same old 'Decision Speed' term in the majority of cases. It was the term that was most commonly used by our training department in the past and I think it still remains stuck in peoples minds.

It may be semantics, but when you are training people I believe it's just sloppy to not give them the proper basics.

Before getting away from this and into Vref issues, are there any EVERGREEN pilots here? I read an article in the Boeing Airliner two years ago which described EVERGREENs policy of 'decrementing' the calculated V1 by a fixed value (8 knots?) and bugging that as V1 in order to cater for delay between Vef and pilot action by V1. I guess you could realistically refer to that new speed as a 'Decision Speed'? Are they still doing this? Does anybody else?

[john_tullamarine]

I suggest that it is very necessary to keep in mind that V1, like a great many other things in this game of aviation, is a certification animal. The strict definition, while of obvious interest to the line pilot, is perhaps not so important as the methodology of the parameter's use as prescribed in the manufacturer's flight and operations manuals and other training material for the specific aircraft.

Airline performance engineering and flight standards management people, on the other hand, must have a good handle on what goes into the certification recipe for a given aircraft so that a company's prescribed procedures do not unconservatively conflict with the flight manual.

As a certification thing, V1 has specific meanings and requirements within the flight test, aerodynamics, and, ultimately, certification disciplines. Certification matters and definitions can, and do, change .. it is then very important that the 'correct' definition be sourced... far too often, training pilots look up the current rules and then endeavour to apply the current rules to an earlier certification philosophy... which may, or may not, be a sensible thing to do. By following the manufacturer's recommended practices (given that the wider Industry never knows more than a fraction of what went on with any given certification) we can have a reasonable confidence that line practice is consistent with the certification.

The question of reducing V1 needs to be looked at in some detail especially in the case of low weight takeoffs where the value may get tangled up with Vmcg considerations. Again, the manufacturer has all the certification detail... any given operator seeing a need to vary the manufacturer's recommendations would need to enter into discussion with the manufacturer to confirm that hidden hazards were not going to be exposed ....

[Captain Stable]

I hear your concerns, John.

As I understand Idunno's post, what Evergreen may have been attempting to address is the problem, in an accelerating aircraft, of the length of time it takes to say (and recognise) the words "Vee wun". I know of several airlines which state that the PNF must say the words in such a way that the finish of the words coincides with V1 being reached. This tends to result in it sounding more like "Veeeeeeeee...... WUN". Others state that if the PF has heard anything sounding like "Ve..." when a failure occurs he must not abort. Perhaps it is long past time that an internal bug can be set on the ASI and an automatic gong (or other sound) is heard that alerts the crew to the requirement to continue the takeoff. We have the technology...

[john_tullamarine]

true, the electronics permit all sorts of easily generated bells and whistles .. .. but to do that sort of thing confers a level of supposed precision onto the real world application of the calculation which is not sustainable ....

I suspect all these little bits of detail serve mainly to confuse the pilot into thinking it is all a bit more precise than it is ...

The whole concept of V1 is a bit rubbery in the real world application ...

... and, as we see so often in the sim with a prearranged incapacitation of PNF ... is PF always monitoring his/her own clocks ? The more the reliance is permitted to be diverted to the support system the more, I suspect, that the decision making process can be compromised ....

[m&v]

Evergreen wasn't the first to 'consider'-Minus v1...Lufthansa,upon reading the 25-109,and the test card,after their incident b747 freighter,hong Kong 83,considered -v1 minus 3knots.This complied to the 'test card'Vef(about 1 sec prior to V1-established by the Manufacturer,as high as 3secs with the centre eng 727)for'recognition'of a failed eng'prior to V1...This all came out,along with the 'Vef'definition, with amendment 42 of the FAA 25-109,as it reads today.(Air Canada tried to use the V1-minus 5'in 1980,but dropped the idea)
JAA we're to understand uses the same criteria,but named diferently'Stop' etc.The A320 complies with the FAA25,and is very exact in the 'low weight'Takeoff case ,in that the V1 must avoid the VMCG area.:rolleyes:

To answer the question:V1 is a commit speed after the 'first' stopping action(whether it be brakes,or 'thrust levers'-Boe/Mdc), if a failure is ' 'recognized' 1 sec',or about 4knots before V1:eek:

['%MAC']

V1 does appear ‘rubbery’ upon examination, there is the FAR part 1 definition, then FAR part 25.107 has a definition, then I came across this from Big Bleu Airlines:

“V1 – The speed at which Maximum Braking is achieved. The speed must not be greater than Vr, is less then Vmbe (max brake energy) and greater than Vmcg (ground minimum control speed). Reverse thrust is not considered in determining runway limit weights or V1. V1 will be called by the PNF (pilot not flying) prior to attaining V1 on the takeoff roll so that the aborted takeoff will be initiated at V1 and not at a point beyond V1” [italics added]

A bit unwieldy, doesn’t really nail it down, it’s between this and that, not greater than so but less than this. Ah right, thankfully there is a quantitative answer in the speed charts.

[Flight Detent]

Hi all,
I was always taught, many years ago, that;

a/ V1 is the maximum speed one can go, and still be able to stop in the runway length remaining.
and,
b/ Vd (Decision speed), is the minimum speed one can go, have an engine failure, and still accelerate and take-off in the runway length remaining. (obviously intended for multi-engined acft!)

Cheers

[mutt]

Thats the first time that i have heard of the term Vd (in an aviation context :) ). I would consider that to be V1min.


Mutt.

[john_tullamarine]

(a) better to leave Vd to represent design diving speed as it always has done in the FARs. The particular aspect of another discipline in which the term is seen we aviators would do well to avoid ....

(b) while V1min is not similarly defined, V1min or minV1 usually relate to Vmcg-limited V1. Mutt's suggestion, though, has much to recommend it.