do influence the decision.

if you say so.

not if you're taking off at performance limited TOW. Whatcha gonna do then

there will be some variation in decision process depending on what part of the performance is limiting ... however if, say, WAT limited .. that's when the Commander exercises command perogative and defers the takeoff. Are you seriously suggesting that, in a case where there is a significant probability of serious windshear AND the aircraft is seriously limited .. you would run the takeoff ?

One has the option of keeping lower V1 and appying higher VR,V2 but again they're both increased

did I miss something ? I was sure that you were talking about min V2 schedules and not increasing speeds to take advantage of improved climb capabilities (regardless of OEM) at speeds modestly in excess of min V2.

whatcha gonna do if your ATOW is equal to RTOW?

.. don't go with a significant probability of windshear .. unless you are a very successful gambler

which leaves one with the option of full thrust and pitch play to remain airborne.

you appear to like running on near empty energy tanks.


Guess we will just have to agree to disagree ?

we'll have to agree or disagree at some stage but in order to do so we need a very concrete practical example. Surely one of those wide bodies taking off from NRT to cross the pond is at RTOW for 10+ flight time. And I haven't seen many of them deferring takeoffs with low level wind shear advisory in effect and officially -+20 knots speed variation being on ATIS. Are you suggesting they're all gamblers? There's theory and practice. That's why I said it all depends on too many factors and rightfully the commander will make a call.

I was talking bout optimized performance speeds and optimum V2/Vs + V1/VR ratios which inevitably leads to V2 being higher as VR. I'll clarify my previous post by saying that for a ATOW=RTOW one is bound to keep VR and V2 but can take a lower V1 or for ATOW<RTOW one can take V1 for ATOW and VR/V2 for RTOW but they always go together. I've never seen VR being higher than V2. That's the whole point of the discussion here.

VR + 20 makes sense if IAS provides reliable indication and isn't screwed up by WS. If the WS hits you at the range close to VR +20 then it's virtually impossible to identify VR+20 as the IAS is all over the place. That's also why I think airbus's concept of optimized speeds and energy management is more efficient. There are many ways to skin the cat that we all agree upon. :ok:

Then, shall we keep the discussion going until we collectively achieve agreement or the alternative ?

Are you suggesting they're all gamblers?

An advertised 20kt shear is a tad different to a snarling tiger of a downburst .. ? One really ought to keep one's goalposts stationary.

rightfully the commander will make a call.

Of course.

I was talking bout optimized performance speeds

We were aware of that ... however, such uses an overspeed takeoff ie you have already increased your VR and V2 which, as a sideline benefit, keeps you further away from Vs.

ATOW=RTOW one is bound to keep VR and V2

That doesn't follow, necessarily. While it would be a risk dilemma in the case of a critical ASDR situation, other limitations may give you a bit of Commander's discretion.

I've never seen VR being higher than V2.

Semantics. If you adopt a VR higher than that scheduled, then the V2 achieved necessarily will increase in line .. regardless of what you might choose to set on the ASI bug.

VR + 20 makes sense if IAS provides reliable indication

Those of us from a different era are concerned less about (a fluctuating) ASI and more about N1s and ball angles. IAS indication is nice to have but not a necessary condition for continued safe flight.

If the WS hits you at the range close to VR +20 then it's virtually impossible to identify VR+20 as the IAS is all over the place.

Some days things just aren't fair, I guess. However, apart from primitive presentations, we all have some sort of GS indication .. I, and most of my olde phart colleagues, routinely monitored that indication .. which then provides something akin to the get out of jail free card in your postulated scenario. Again, the wise Commander, for the great majority of occasions, will have made a sensible call according to the reasonable to infer likely outcome of the present weather .. prior to commencing the takeoff roll.

There are many ways to skin the cat that we all agree upon.

Absolutely the case, good sir.

I have used the Boeing procedures we had and have always felt very comfortable with increasing V speeds with wind shear possible using max TO wt speeds. With long runways and possible winds shear I always added speed. It helped us one day landing at Portland when tower reported turbulence on final in rain and 30 knot direct crosswind. I added 20 knots and at 100 ft lost that 20 knots in windshear. I got a great landing but when I cleared the runway a United 727 was landing and their touchdown was the worst I have ever seen. My captain said United I would check your wingtips. They may have gotten both of them with their multiple touch downs. Nose gear too.

Curious...do your SOPs state to not do reduced thrust departures when windshear and microbursts might be evident in the area?

VR>V2 that's what caused the whole perplexity, not speeds increments in line.

I take it the crew simply misinterpret the sentence of increasing all V speeds to the performance limited TOW. The way I read it is that if TOW is below the RTOW than one has the option to apply RTOW speeds but VR increment is limited to TOW +20 Max. However all speeds are increased in line. Airbus does the same by applying the optimized speeds which are rather in the upper range.

Interesting enough Boeing in the very next sentence recommends following:

That however contradicts the very idea of having higher speeds.

As for how to determine the point of rotation Boeing does make a sensible recommendation of Well, that settles it for me at least.:ok:

following applies to V2
JAR 25.107 Subpart B FAR 25.107 Subpart B
V2 is the minimum climb speed that must be reached at a height of 35 feet above the runway surface, in case of an engine failure.
“JAR/FAR 25.107
(b) V2min, in terms of calibrated airspeed, may not be less than:
• 1.13 VSR1 (JAR) or 1.2 VS (FAR) for turbo-jet powered aeroplanes [...]
• 1.10 times VMCA
(c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by JAR 25.121(b) but may not be less than:
• V2min; and
• VR plus the speed increment attained before reaching a height of 35 ft
above the take-off surface.”
This speed must be entered by the crew during flight preparation, and is represented by a magenta triangle on the speed scale (see Figure C3).

I'm curious how many chief pilot culled robots we have in here that would hold a calculated V2+wind-shear speed right into a building after rotation during a micro burst.

Tad silly you are no?Back in the cave.:E

No, it doesn't.

If you encounter windshear prior to rotation, the biggest threat is runway overrun, therefore the Boeing procedure is to rotate at the actual TOW Vr, or the last 2000ft of the runway, whichever comes first.

That is the main reason for calculating both speeds.

If you DON'T encounter windshear on the runway, you may delay rotation, thus taking extra IAS into the air, where it will be beneficial in out-performing windshear if encountered.

None who've read the book. Windshear escape involves TOGA thrust, an initial target attitude, then whatever attitude is needed to maintain a positive climb and avoid terrain, while respecting the PLIs (which denote onset of stick-shaker).

However it's achieved, being at a higher IAS when windshear is encountered will increase your chances of surviving it.

@ Wiz, Boeing speaks bout AT or AFTER the VR but never mind. I get the idea and it makes sense. What I can't visualize is having 2 VR on your speed scale. How doest it work? Do you insert 2 values or just one and keep the other one in mind? Kinda weird procedure. It's logical that approaching the end of the strip full steam the only viable option is to rotate and wait. Airbus is very simple in this regard, one set of speeds and that's it. GS indication is irrelevant for the lift equation but remaining runway is certainly a clue. :ok:

True, but that would also apply to encountering Windshear before Vr, and making a "Go" decision.

The Vr for ATOW is bugged. How to handle the different speeds in practice isn't specified, so is a matter to be briefed.

A common practice is to call "Vr" at ATOW Vr, them " Rotate" at the increased speed.

This thread kind of makes the argument against reduced thrust departures doesn't it?

Reduced thrust takeoffs should not be made when the runway is wet or contaminated with snow/ice, or when windshear is possible. Otherwise, it saves a whole lot of wear and tear on the power plants.

unfortunately, with reduced spacing on departures, windshear (wake turbulence) is a given..
right now its not about if, but the severity of the encounter...

FP OBN:

Horse pucky.