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Check Airman
4th Aug 2012, 05:22
Gents,

I had an interesting discussion today, and would like your take.

Our manual provides guidance when departing when windshear conditions may be present. One thing we do is to increase Vr, and it tells us exactly how to determine the increment. What it does not say is what to do about V2.

We found a scenario where the Vr increment would cause Vr > V2. That just doesn't seem right. Doing some homework, FAR25 doesn't address this issue.

Is this correct? Can Vr exceed V2?

YGBSM
4th Aug 2012, 05:29
Why not? What does one have to do with the other?

We increase Vr as well during windshear ops.

Wizofoz
4th Aug 2012, 05:49
Increased Vr procedures are simply a matter of using the excess performance available when operating at less than Performance Limited TOW to mitigate against the possibility of Windshear.

The philosophy is that, if you can rotate at a certain speed and comply with the field length and climb gradient at a limiting weight, you will CERTAINLY also meet the requirements if you rotate at that speed at a REDUCED weight.

If you were to use all three v speeds and thrust setting for RTOW at a lower weight than they were calculated for, you would still achieve an excess of performance.

BUT your BEST performance for your current weight engine out will be achieved at v2-v2+15 for your ACTUAL weight.

SO- take the extra energy from the increased Vr into the air, as an extra buffer against windshear after lift-off.

HOWEVER if you encounter windshear on the runway OR have an engine-out, revert to the best performance for you ACTUAL weight- the V2 you have calculated

bubbers44
4th Aug 2012, 05:54
Our sim checks we know we will get a wind shear so increase VR and rotate slowly to make sure we don't get behind the power curve. In real life you may not know this is going to happen but in the sim you always will. It is a game so you have to play it.

Wizofoz
4th Aug 2012, 06:23
Windshear is almost always associated with specific, reported, predictable atmospheric conditions.

If it takes you completely by suprise, chances are you weren't paying attention.

Microburst2002
4th Aug 2012, 07:12
If it takes you, by surprise or not, you will hear: why did you take off in the first place?

mutt
4th Aug 2012, 10:47
Check Airman, what you are doing is very similar to "improved climb", usually Boeing manuals state that if you increase Vr, then increase V2 by the same amount, it defeats the purpose if you accelerate to a higher Vr and then lose that speed increase by slowing down to the original V2.

Mutt

Wizofoz
4th Aug 2012, 13:02
Sorry, mutt, not true.

Improved climb is a MTOW Enhanching procedure.

Normal take-off charts are calculted using a "Standard" V2 os 1.2Vs. Improved Climb is a seperate set of charts allowing a longer takeoff roll to achieve a higher v2, and thus a better climb gradient- but it is not specifically related to windshear.

With the advent on computer based OPTs, EVERY takeoff is "Improved climb".

Increased Vr is a suplementary procedure specifically related to windshear mitigation, and you do NOT increase the V2 as part of it.

And Micro- I agree with you! If I were suspicious enough of Windshear to use an increased Vr, I'd probably decide to wait the conditions out instead.

john_tullamarine
4th Aug 2012, 13:54
Increased Vr is a suplementary procedure specifically related to windshear mitigation, and you do NOT increase the V2 as part of it.

My comments are generic.

(a) nil windshear, as it turns out, if you increase VR then, OEI, you will end up with a higher than scheduled V2 .. the two being tied up with the rotation rate. AEO, you will end up with a modestly significant increment above V2 anyway. Mutt's comment probably could have been clarified ..

(b) if you actually end up in a significant windshear situation, then V2 becomes a bit irrelevant ..

(i) OEI ... shouldn't have got out of bed that day. Crash, burn, die in all likelihood.

(ii) AEO ... you'll be going for the feathers or whatever is equivalent on your particular machine. V2 is of no interest at the time and has no relevance to survival.

Wizofoz
4th Aug 2012, 14:06
John,

Specific to the 777 we have a supplementary procedure whereby you set all speeds normally, but then ALSO calculate the Vr for RTOW, to a maximum of normal Vr + 20 knots.

If you suspect windshear may be encountered, you may delay rotation until this higher speed, but V2 is calculated and set in the MCP normally.

john_tullamarine
5th Aug 2012, 01:05
If you suspect windshear may be encountered, you may delay rotation until this higher speed, but V2 is calculated and set in the MCP normally.

That sounds pretty sensible to me .. but, in the event of windshear, it follows that you disregard the bugged V2 and go for the indications on the ball ?

Similarly, if you don't have windshear, you are not going to reduce to the bugged V2 but, rather, keep whatever you end up with up to a sensible overspeed margin ? With the OEI caveat relating to very close in obstacles, to reduce speed would be a tad silly, I think.

stilton
5th Aug 2012, 05:53
Best avoided in the first place but, we have the same procedure and I never thought much of it.



If there's windshear around and you encounter it I would much prefer to be in the air with altitude beneath executing the recovery technique than still on the runway, with too high a groundspeed to stop and insufficient IAS to lift off.

:eek:

FullWings
5th Aug 2012, 10:02
Interesting. We don't have a procedure on our 777s for increased Vr for suspected windshear (we have the Improved Climb mentioned earlier) but we do go full length, full power and F15. Or not go at all, which is the preferred option!

IMHO, problems are caused by no differentiation between wind shear and wind gradient and the ambiguity present in most manuals about procedure.

I've come into LHR on a nice day with 15-20kts down the runway with "Windshear reported, loss of 5kts at 200 feet" on the ATIS. No sh*t Sherlock! What were we expecting here? All around, people with shiny new stripes are briefing for W/S G/A, lining up with full power on the brakes, etc.

You also get "Windshear advisories in effect" at US airports, which I take to mean the system is working, not that there are actual windshear conditions present. I haven't been able to find a reference - does anyone know whether this is a correct interpretation?

de facto
5th Aug 2012, 10:51
IMHO, problems are caused by no differentiation between wind shear and wind gradient and the ambiguity present in most manuals about procedure.

Agree,much confusion about the term of wind shear.
Windshear recovery techniques,increase of max VR are for thunderstorm produced windshear,not temperature or wind shears which may require extra handling work/go around but dont necessitate such drastic recovery techniques..

I think posters not taking off in windshear conditions here imply convective related WS.

lining up with full power on the brakes, etc.

That would be useless in terms of performance and contrary to the FCTM for take offs in windy conditions,,,,(engine surge...)

Wizofoz
5th Aug 2012, 13:36
If you suspect windshear may be encountered, you may delay rotation until this higher speed, but V2 is calculated and set in the MCP normally.

That sounds pretty sensible to me .. but, in the event of windshear, it follows that you disregard the bugged V2 and go for the indications on the ball ?

Similarly, if you don't have windshear, you are not going to reduce to the bugged V2 but, rather, keep whatever you end up with up to a sensible overspeed margin ? With the OEI caveat relating to very close in obstacles, to reduce speed would be a tad silly, I think.

If you encounter windshear you fly the windshear escape maneouvre, which is based on attitude and stick-shaker,not IAS.

Tarket IAS for a normal take-off is V2+15-V2+25, so the extra "OOMPH" will probably just leave you at the upper end on that.

FlightPathOBN
5th Aug 2012, 19:16
wake turbulence is windshear.....

MarkerInbound
6th Aug 2012, 01:45
Out of the FAA Controllers Handbook:

3-1-8. LOW LEVEL WIND SHEAR/MICROBURST ADVISORIES
a. When low level wind shear/microburst is reported by pilots, Integrated Terminal Weather System (ITWS), or detected on wind shear detection systems such as LLWAS NE++, LLWAS-RS, WSP, or TDWR, controllers must issue the alert to all arriving and departing aircraft. Continue the alert to aircraft until it is broadcast on the ATIS and pilots indicate they have received the appropriate ATIS code. A statement must be included on the ATIS for 20 minutes following the last report or indication of the wind shear/microburst.
PHRASEOLOGY-
LOW LEVEL WIND SHEAR (or MICROBURST, as appropriate) ADVISORIES IN EFFECT.

sevenstrokeroll
6th Aug 2012, 02:29
whizofoz

and bubbers 44

whiz...your own statement says: almost always...not always.

It is entirely possible that you may observe meteorological clues that might lead you to believe windshear/microburst is possible...but not assured...so, do you sit on the ground for a couple of hours or do you add speed to Vr to help out?

IF windshear/microburst was totally avoidable all the time by a simple metric of temps, wind and so forth, we would do it. And doppler radar isn't available everywhere.

I was in CLT when a DC9 crashed during approach/go around and it was blamed on microburst among other things. I watched the smoke come up...I knew I wasn't going to takeoff in that crap.

I observed the weather personally as I was doing my walkaround. the sky was green, the storm had EVIL in it 10 miutes before the crash...but there is no requirement for ATC to advise you that if you continue you will die.

windshear is still in the infancy of predicting and avoiding, so Bubbers 44 is right...you never know and 99.44percent is not good enough

Dan Winterland
6th Aug 2012, 04:10
I used to fly an aircraft where VR was always greater than V2. We never calculated V2 as it was assumed we would never fly below VR!

bubbers44
6th Aug 2012, 05:09
I was waiting for my pax one day in Oklahoma flying a Falcon 20 as captain. Reports were a storm was approaching the airport with hail and a tornado warning. I had the plane put in a hanger until it passed and told my pax we had to wait until it passed. I watched the last take off, a twin engine Cessna take off with a 10 knot headwind. As he passed the end of the runway the wind switched to a 40 knot tailwind with heavy rain. He was very lucky. If we had taken off behind him we would not have made it. As SSR said don't count on luck with wind shear. It might not be your lucky day.

Dan Winterland
6th Aug 2012, 05:55
Here's a tip. If there's a big black cloud over the airfield and you're worried about windshear or microbursts, keep an eye on the OAT guage. If it drops about 5 degrees all of a sudden, don't go. It's the cold air from a downdraught hitting the ground and spreading out. Not conduscive to safe aircraft operating!

stilton
6th Aug 2012, 06:11
Seriously good tip Dan.


'I used to fly an aircraft where VR was always greater than V2. We never calculated V2 as it was assumed we would never fly below VR! '



Come on, you have to let us in on the type now..

sevenstrokeroll
6th Aug 2012, 06:27
watching OAT is a vital part of assesing the microburst threat.

I personally have spoken with the FAA administrator and deputy administrator on the subject of wx and flying...they still have not executed the advice I gave them.

Check Airman
6th Aug 2012, 06:30
Thanks for all the helpful replies. I suppose once you're airborne, you fly your normal V2+15 (if no windshear), but it just felt wrong on so many different levels to see the speed bugs arranged that way. Live and learn.

You also get "Windshear advisories in effect" at US airports, which I take to mean the system is working, not that there are actual windshear conditions present. I haven't been able to find a reference - does anyone know whether this is a correct interpretation?

You're pretty much right. Any major US airport almost always has windshear advisories in effect- a lot like the warning like birds in the vicinity of the airport.:rolleyes:



Here's a tip. If there's a big black cloud over the airfield and you're worried about windshear or microbursts, keep an eye on the OAT guage. If it drops about 5 degrees all of a sudden, don't go. It's the cold air from a downdraught hitting the ground and spreading out. Not conduscive to safe aircraft operating!

Thanks for that tip Dan. While waiting out some wx the other day, the ATIS temp fell 3-4 degrees with an associated wind shift. I'll certainly keep that information handy.

bubbers44
6th Aug 2012, 06:40
After the ORD DC10 incident we didn't have to slow to V2 any more. If we were doing fine at V2 plus 15 we could maintain it. I would have done it anyway but the corporate guys had to come up with it. Now the stabilized approach is the big thing. ACARS transmits descent rate and airspeed so any deviation from standard is sent to dispatch. Lots of go arounds for no reason I am sure. Retirement is wonderful.

9.G
6th Aug 2012, 08:18
interesting to see once again completely different philosophies entertained by Boeing and Airbus. On the bus it's straight forward either delay the whole thing or TOGA but no such thing as changing the speeds etc. That kinda makes sense coz we have both predictive WS and active WS warnings. :ok:

Dan Winterland
6th Aug 2012, 13:32
"I used to fly an aircraft where VR was always greater than V2. We never calculated V2 as it was assumed we would never fly below VR! "


The Victor MK2. With inboard engines, there wasn't a huge assymetric effect, although VMCA was a factor in a double assymetric go around as the rudder was quite small. The four speeds we used to calculate before take off were V1, VR, VPAT which was the heavyweight circuit pattern speed and VEPS (V Emergergeny Parachute Stream) - the speed we had to get below after touchdown at takeoff weight before we could deploy the brake chute to prevent shredding it.

The MK1 Victor was operated to military performance which being calculated in the early 1950s was essentially "as is" and was gross performance. The MK2 was the first aircraft to be powered by the RR Conway and as part of the Conway's cetifiction process, the aircraft worked to BCARs net performance, hence the slightly complicated calculations.

john_tullamarine
6th Aug 2012, 14:05
That kinda makes sense coz we have both predictive WS and active WS warnings

.. and limited, finite energy.

If the available energy on the day the procedure is put to the test is not-quite-up-to-it then the alternative procedure with an extra 20kt or so ... might just make the difference between success and failure.

Of course, the particular met circumstances may defeat the Boeing procedural approach as well .. but the latter, for the intermediate circumstance .. offers the better overall risk plan, I suggest.

9.G
6th Aug 2012, 16:43
J.T. we all agree that energy is the key to survival. It well depends what kinda WS hits and at what moment. Too many uncertainties. IAS is meaningsless as speed fluctuations are too big. That's the reason why airbus created the magic tool SRS which keep a min level of energy in case of WS encounter. No need to increase VR Alpha Prot simply doesn't allow airbus to stall in case of full stcik back and that's what we do in case needed. That's pretty much one can do with full thrust. :ok: That makes the difference in level of sophistication between airbus and boeing.:ok:

john_tullamarine
6th Aug 2012, 22:40
That makes the difference in level of sophistication between airbus and boeing

That may be quite true - I have a background on Boeing only.

However, in the case where the energy balance isn't quite going your way then your statement

That's pretty much all one can do with full thrust (my correction of the presumed typo)

clearly is not correct. The use of an overspeed margin provides more energy to trade and greater energy overall ... with a better probability of survival.

No need to increase VR Alpha Prot simply doesn't allow airbus to stall in case of full stcik back and that's what we do in case needed

No doubt in my mind that that is a wonderful tool. However, the aim of the game is to miss the ground so not stalling is only part of the equation. Presuming that the critical obstacle were not very close in, the extra knots still provide the better option in my mind.

It comes down to a case of risk assessment and management. Nothing wrong with the basic philosophy but the use of a few more knots, especially if the runway is not critically close in obstacle limited .. just might make the difference between a few beers more than usual in the bar that night .. or not needing the beers at all.

aterpster
6th Aug 2012, 23:59
j.t.

It comes down to a case of risk assessment and management. Nothing wrong with the basic philosophy but the use of a few more knots, especially if the runway is not critically close in obstacle limited .. just might make the difference between a few beers more than usual in the bar that night .. or not needing the beers at all.

Such as a takeoff in an L1011 on KJFK's Runway 13R (14,500) going to the other coast. It was raining hard (not TRW, rather a March 'noreasterly) with surface winds gusting to 50 knots and 100 knots reported at 1,500.

A very slight climb until V2 +50 then up into the muck.

Denti
7th Aug 2012, 04:26
@9.G, on the Boeings I've flown it is a mandatory full thrust take off as well if windshear is suspected or reported (which usually means bigger thrust increase as normal take offs usually use thrust reductions greater than 30%), and of course they have the full suite of predictive and active windshear warnings as well. Some of those pws warnings are inhibited during take off though, new caution alerts between 80kts and 400ft AGL, new warning alerts between 100kts and 50ft AGL, existing alerts remain active. Nothing wrong with using that 30% extra thrust on the ground to gather some energy in the form of a few knots more speed before attempting rotation, it just provides a bigger energy margin during the event.

9.G
7th Aug 2012, 07:03
J.T & Denti, I have no problems with extra speed. Any extra energy will be helpful. In practise however, how will you determine that you're now 20 Kts plus if your speed indication all over the place. I presume we're talking bout a real WS here +- 20 kts, at least. I'm not talking bout LHR WS warning as per usual, those're beer shakers. I'm talking bout the once in the far east NRT, TPE, HKG or US east coast. Being within a 50 kts waring zone of a TD, let alone a typhoon you can already pretty much forget your IAS indication. How will you know you're At the point of VR+20 with speeds fluctuations of at least +- 20 kts unless you got so much runway that one can just sit it out and rotate as per arse feeling. J.T. SRS will provide a min climb rate of 300ft/m for WS conditions, if followed the FD. If the WS is so severe, we're talking downburst now, then Aplha Protection will at least keep the a/c alfoat so to speak. Not changing the config is supposed to soften the blow apart from not disturbing the air flow for better lift initialy. In thoery it sounds nice, in practise all depends.:ok:

john_tullamarine
7th Aug 2012, 08:23
A very slight climb until V2 +50 then up into the muck.

I'm with you, sir.

In thoery it sounds nice, in practise all depends.http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/thumbs.gif

I'm sorry to be a tad obtuse ... olde phart disease at play again, you see ..

If conditions are such that one can't conduct an overspeed takeoff with even a remote degree of safety, then what permits the safe conduct of an on min speed takeoff under the same conditions ?

Something doesn't quite gel. Perhaps you could re-read your post and contemplate the apparent illogic ?

Alternatively, one might perhaps be better served going back to the pub in such conditions and toasting the brave folk who took off ?

9.G
7th Aug 2012, 08:43
Alternatively, one might perhaps be better served going back to the pub in such conditions and toasting the brave folk who took off ? Well. that's always the best solution, no doubts. I'm not against that extra 20 Kts at all I'm just trying to comprehend how it's supposed to work in reality. I've never seen it or heard of it before.
If conditions are such that one can't conduct an overspeed takeoff with even a remote degree of safety, then what permits the safe conduct of an on min speed takeoff under the same conditions ? Well, the answer is simple- dynamic of the situation and knowledge of local particularites. NRT for instance can have severe LVL WS on a clear sunny day with anticyclone weather. It's on the ATIS with announced +- 20 Kts speed gain and drop most of the time associated with cross winds and yet the show goes on. So it all depends on when it hits you with what magnitude. Aviation had to be seized in the far east for at least 3 months following the beer is better than WS philosophy yet it goes on. :ok:

P.S. I should probably clarify the reasons of being perplexed. While airbus is basing it's entire philosophy on the concept of energy installing sophisticating tools to keep that min level of enegry recognizing the fact that IAS is meaningless in case of WS with the range of total 40 Kts. Boeing solved the problem of kinetic energy by adding 20 Kts to VR. When VR+20 is indicated and rotation is inititated and in the very next instant it's -40 Kts where does it leave one?

9.G
7th Aug 2012, 09:42
just checked 777 manuals:
Consider increasing Vr speed to the performance limited gross weight rotation speed, not to exceed actual gross weight Vr+20 knots. Set V speeds for the actual gross weight. Rotate at the adjusted (higher) rotation speed. This increased rotation speed results in an increased stall margin, and meets takeoff performance requirements. If windshear is encountered at or beyond the actual gross weight Vr, do not attempt to accelerate to the increased Vr, but rotate without hesitation. That's quite a different statement. :ok:

john_tullamarine
7th Aug 2012, 10:50
I'm just trying to comprehend how it's supposed to work in reality

It's all to do with energy (presuming that one has some spare runway in the first place). Think of a bucket of water progressively emptying .. when it's gone, it's gone. A bigger bucket lasts a tad longer .. perhaps just enough to get over that knoll off the end of the runway ?

Well, the answer is simple- dynamic of the situation and knowledge of local particularites

Actually, I think that doesn't mean much at all, does it ?

where does it leave one

Much the same place as with an Airbus, I suggest.

That's quite a different statement

... but quite reasonable and consistent with the general story.


.. methinks perhaps you have been seduced by the razzle dazzle ?

9.G
7th Aug 2012, 11:16
Actually, I think that doesn't mean much at all, does it ? It does to me coz dependable on what's the origin of the WS and how it's been determined, terrestrial or purely weather induced and how it's been determined based on Pireps or measured, do influence the decision.

but quite reasonable and consistent with the general story.

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

Much the same place as with an Airbus, I suggest. Perhaps, but on the bus, if at all, V2 is increased as well. One has the option of keeping lower V1 and appying higher VR,V2 but again they're both increased. Though I agree that in case of WS the goal is to stay airborne.

Wizofoz
7th Aug 2012, 11:20
Did you miss this part?

not to exceed actual gross weight Vr+20 knots.

So, if RTOW Vr is more than 20kts greater than ATOW Vr, you may use up to Vr+20- as John has been explaining.

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

If you're performance limited, you're performance limited. whether you're in an Airbus or a Boeing.

But if you HAVE extra performance at hand, why not use it?

9.G
7th Aug 2012, 11:25
Wizofoz, whatcha gonna do if your ATOW is equal to RTOW? :ok:

If you're performance limited, you're performance limited. whether you're in an Airbus or a Boeing. which leaves one with the option of full thrust and pitch play to remain airborne.

john_tullamarine
7th Aug 2012, 12:22
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 ?

9.G
7th Aug 2012, 15:18
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.

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. 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:

john_tullamarine
7th Aug 2012, 22:09
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.

bubbers44
7th Aug 2012, 23:12
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.

Sillypeoples
8th Aug 2012, 01:48
Curious...do your SOPs state to not do reduced thrust departures when windshear and microbursts might be evident in the area?

9.G
8th Aug 2012, 09:06
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:

If windshear is encountered at or beyond the actual gross weight Vr, do not attempt to accelerate to the increased Vr, but rotate without hesitation. 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 Windshear encountered during takeoff roll:
• If windshear is encountered prior to V1, there may not be sufficient runway remaining to stop if an RTO is initiated at V1. At VR, rotate at a normal rate toward a 15 degree pitch attitude. Once airborne, perform the Windshear Escape Maneuver.
• If windshear is encountered near the normal rotation speed and airspeed suddenly decreases, there may not be sufficient runway left to accelerate back to normal takeoff speed. If there is insufficient runway left to stop, initiate a normal rotation at least 2,000 feet before the end of the runway even if airspeed is low. Higher than normal attitudes may be required to lift off in the remaining runway. Ensure maximum thrust is set. 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).

Sillypeoples
8th Aug 2012, 19:42
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.

de facto
9th Aug 2012, 04:19
Sillypeoples
*
Join Date: May 2012
Location: Earth
Posts: 47
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

Wizofoz
9th Aug 2012, 05:20
That however contradicts the very idea of having higher speeds.

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.

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.

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.

9.G
9th Aug 2012, 10:26
@ Wiz, 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. 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:

Wizofoz
9th Aug 2012, 13:33
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.

Sillypeoples
9th Aug 2012, 23:56
This thread kind of makes the argument against reduced thrust departures doesn't it?

aterpster
10th Aug 2012, 00:43
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.

FlightPathOBN
10th Aug 2012, 00:58
unfortunately, with reduced spacing on departures, windshear (wake turbulence) is a given..
right now its not about if, but the severity of the encounter...

aterpster
10th Aug 2012, 02:14
FP OBN:

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

Horse pucky.