Windshear

[bobdazzle]

I want an opinion of the majority of experienced pilots on this forum:

Simulated windshear on takeoff- exercises in SIM always warrant a nose down after f/d transitions from pitch to speed mode just after takeoff in windshear.

I am of the opinion that in severe windshear an attitude of 15 degrees should be established even if windshear protection/ guidance is available.

The reason I think so is coz, Severe windshear mostly comes as a surprise or shock (unlike in simulator when one is expecting it) / lowering the nose while flying manually (while following f/d guidance) to recover airspeed cannot be achieved as precisely as maybe the autopilot does it (especially so in turbulent flight conditions and just like autolands cant be done manually by following f/d guidance) / Indicated decreasing airspeed may be false in a tailwind shear while groundspeed may be constant and the situation may not warrant a lower pitch attitude / Lowering the nose in a downdraft may be accentuated because of the draft itself and may not be recoverable.

Appreciate your thoughts.

[PEI_3721]

Apart from ‘Granny sucking eggs’ – why should you be taking off … …

The FD command might depend on the mode design. If there is a dedicated windshear mode, based on a detection and warning system, then the pitch demands might trade energy according to altitude; speed preference if higher, or sacrifice speed at lower altitude. However in most situations it could be expected that in a decreasing energy condition the nose would be lower than for a normal takeoff, but initially the nose might be higher when trading energy up to the stall warning ‘attitude’.

There might not be a definitive answer, thus fly the FD if windshear enabled otherwise use the recommended initial pitch target and adjust that (reducing) to respect stall warning.
Some (many) simulations only consider a conventional headwind / downdraught situation; in these the attitude change could be expected to be nose down. However real encounters could range from a side-slice through the core downburst to a tail encounter after lifting off in the down burst.

A real approach example might help:- http://www.scribd.com/doc/35984283/Windshear-Incident

[glendalegoon]

I see your points.

the 15 degree pitch target is a good one for most planes (though I think the f100 had a 12 degree target, not sure).

but a dedicated and properly operational windshear guidance system is something that might over ride the 15 degree pitch.

I would ask your simulator instructor. And yes, I know: avoid, avoid, avoid. But its a sim!


Does your airline allow you to use higher v speeds for takeoff (IE if you are 10,000 lbs below max takeoff for runway in use, can you use the max weight for runway v speeds to have more energy when breaking ground?)

[AirRabbit]

I really wish we could find a way to use a simulator the way it was intended to be used … as a training tool to sharpen the skill sets we all use to fly airplanes. When we approach tasks presented to us in the simulator as a simple “simulator exercise” that can, and some would say, should, be ignored once the simulator session is completed, we are negating the most useful tool available to us. We all should fly the simulator JUST as we fly the airplane … no more … no less. Yeah … I know about the “nay-sayers” that insist that a simulator is not and never will be the airplane – and therefore should be treated as a necessary inconvenience that we all have to endure. Well, the first part of that statement is true – yes, you read that correctly – a simulator is not, and VERY likely never will be, an airplane. But the balance of that statement is vehemently NOT true. We should treat and respond to the simulator just exactly as we would in the airplane – and those cases where there is more information that we might be able to discern in the airplane SHOULD be provided by the instructor. This is precisely why I have continually advocated a total overhaul of the way we train our instructors. Today, way too many instructors merely “program” the simulator and let the simulator do the “teaching.” WRONG! With the involvement of a good instructor, the use of the most ancient of simulators can be, and is, used to train and evaluate competent pilots all the time. If the instructors didn’t know their job as well as they do … the students going through would likely be able to open, enter, start, and fly the airplane – reasonably well – particularly if the airplane had been maintained in the pristine condition we all would like to find our airplanes … and this would last until some malfunction occurred or the pilot was asked to fly that airplane into conditions that were less than ideal.

Training should never be considered, or treated as, a necessary “evil” through which all must pay their dues to get the privilege of flying (playing with?) the airplane. AND simulators should never be relegated to a position of anything less than the very best tool available to allow pilots to learn, practice, and polish the skills they require to do the job (admittedly, a very rewarding job – but a job nonetheless) of flying that airplane. This particular tool is continually being re-thought, re-tooled, re-calibrated, and depended upon – and any of you with a history longer than a couple of decades can attest, first hand, to the advancements simulation has undergone … and that kind of advancement in technology and presentation continues today … and it is increasing at an accelerated rate … all to the good. Please … let’s not disparage such an important tool -- and let's not get ourselves wrapped around the "increase/decrease V-speeds whenever you're nervous" axle yet again.

[glendalegoon]

air rabbit

increasing v speeds as I mentioned is part of our airlines FOM. Approved by the FAA POI.

again folks, if your takeoff weight is max minus 20,000 lbs, you could use the max numbers and have more energy at liftoff and still the same protections as if you were at max takeoff weight for a given runway. Does your's have this?

[Pace]

:EBobDazzle

I was flying a month back in those extreme wind conditions Hurricane force winds reaching 80 KTS shop fronts blown in, power cables blown down and lorries blown over. even the poor marshaller got blown off his feet.

Going Into Doncaster at Night the winds were 49 gusting up to 80 its but only 10 to 20 degrees off the runway.

This was in a Citation and the worst I have experienced! IAS I kept at 170 its and experienced large wing drops as well as speed fluctuations from 170 KTS to 120 KTS.

What can I say. At one point I did not think it was laudable and yes I was scared to reduce speed until very late when the air smoothed somewhat and surprised myself at the smooth touchdown some 20 its above VREF

As bad was taxiing in when going crosswind it took me and the FO to hold the controls

Do not relish doing that again

[AirRabbit]

again folks, if your takeoff weight is max minus 20,000 lbs, you could use the max numbers and have more energy at liftoff and still the same protections as if you were at max takeoff weight for a given runway
...and what do you recommend doing if an engine failure occurs just prior to the newly established (now increased) V1 speed? Continue the takeoff although you haven't yet reached V1 ... OR ... do you reject the takeoff when you've long past the "real" V1??

[Brian Abraham]

increasing v speeds as I mentioned is part of our airlines FOM. Approved by the FAA POICould you scan and post the relevant page. My impression was that the aim was to maximise climb gradient. You're not going to do that by artificially increasing V speeds.

Recovery Technique for Windshear Encounter during Takeoff

Select the minimum flaps configuration compatible with takeoff requirements, to maximize climb-gradient capability

Set the thrust levers to the maximum takeoff thrust (TOGA)

If windshear is encountered during takeoff roll (excursions greater than 15 knots), apply the following recovery techniques without delay:

Before V1:

Reject the takeoff only if unacceptable airspeed variations occur and the pilot assesses there is sufficient runway remaining to stop the aircraft.

After V1:

Rotate normally at VR

Follow the Flight Director pitch orders, or set the required pitch attitude if FD is not available (as recommended in the applicable FCOM).

Note: If a windshear occurs during takeoff roll, V1 may be reached later (or sooner) than expected. In this case, the pilot may have to rely on his/her own judgment to assess if there is sufficient runway remaining to stop the aircraft, if necessary.

[Denti]

Increased V-speeds are the norm for us. On our boeing performance tool it is called improved climb speed schedule and can increase speeds by up to 30kts if conditions allow that.

It is supposed to give a better chance to get out of a windshear encounter, although that is only a side effect, mainly it is used to reduce thrust further in climb limited scenarios. Main aim of the improved climb speeds is to improve climb gradient. However in cases where windshear is expected no decreased thrust take off is allowed anyway, therefore we probably will have improved climb speeds up to the maximum which gives a larger margin or more speed to trade in case a windshear happens.

[PEI_3721]

Many aspects of windshear training and SOPs imply that with skill and procedure any encounter can be managed.
Whilst the previous example is a remarkable instance of success, for both skill and circumstance, anything less would have been fatal, e.g. entering the shear below 800ft or any less responsive flight path management.

Sim training is a valuable aid for skills training, but for windshear these skills more likely will only be required following inappropriate judgement of the conditions which enable an encounter.
Similarly SOPs imply that a takeoff using alternative configuration or speeds, and modified handling will be safe.
The skills and procedures are invaluable for any undetected encounter, but perhaps greater emphasis should be made in training and procedures for detecting and avoiding such situations. Windshear is akin to the ground in a CFIT accident. Just because you can ‘do it’ in the simulator or have done it for real, or follow SOPs, is meaningless in a real event, particularly if the encounter is 35 ft lower or the pitch-power is marginally off target.

[glendalegoon]

air rabbit

we use the new speeds and stick with them. that's about as easy as I can make it for you. the new speeds will provide for scheduled performance in going or stopping. and more energy in a windshear encounter right after takeoff.

BRIAN:

as my company's FOM is propriety in nature I will not scan it for you.

However, you can purchase at least one good book on the subject called, "FLY THE WING". It is described there too and is not propriety. The latest edition. Not the earlier editions.

You both sound like you don't believe it. Well, that's ok too. But its true and approved by the FAA as part of our Flight Operations Manual.

DENTI seems to understand quite well. Thanks for backing me up. Wondering why these two don't have it in there FOM. Unless?

[glendalegoon]

PS

climb gradient is lovely, but the idea is to keep flying until you pass the shear/microburst and recover to normal flight.

the longer you can fly, the better chance to exit the microburst

[Brian Abraham]

Thanks Denti. I found a very good thread at http://www.pprune.org/tech-log/492162-vr-v2.html to which you made contribution.

[AirRabbit]

we use the new speeds and stick with them. that's about as easy as I can make it for you. the new speeds will provide for scheduled performance in going or stopping. and more energy in a windshear encounter right after takeoff.
So … if I’m reading your posts correctly – your company manual allows you to arbitrarily reduce V1 by some individually desired amount (this is done to help ensure that the cockpit announcement of V1 can be started AND ended prior to actually passing V1 speed – because it takes so long for someone to actually say, out loud, the words “Vee One”) … and that same manual allows you to arbitrarily increase V1 (and this is accomplished by using an exceptionally higher gross weight than the airplane actually weighs). The bottom line is that your company authorizes each pilot – presumably each Captain – to select a V1 speed – either higher or lower than the derived V1 – by an amount deemed appropriate by that pilot (Captain), and this is authorized because the availability of these alternatives provides for “scheduled performance in going or stopping” and, at the same time, provides “more energy in a windshear encounter right after takeoff.”

I suspect that there are those, other than “yours truly,” who visit/post on this forum who find this kind of logic to be decidedly absent any logic and at the very minimum, self-contradictory. To me it would appear that the company could save at least some money by removing any references to “V-speeds” from that manual and simply allow each pilot (captain) to use whatever speed he/she desires – since there doesn’t seem to be an aerodynamic, a scientific, or a mathematical justification for the use of any particular number because of changing environmental conditions and personal preferences. It is, to say the least, an interesting approach to aviation.

[glendalegoon]

air rabbit

I don't know if it is worth my time to explain things to you. Really, try to understand the subject at hand.

let' say that the max takeoff weight for a plane is 200,000 lbs for a particular runway.

let's say that actual takeoff weight for the same plane is 180,000 lbs for the same runway.

since the plane could takeoff at 200,000 lbs, but is only at 180,000 lbs an increase in speed to the 200,000 lb weight speeds is allowed if windshear is possible. in this way the plane will have more energy at takeoff for an encounter with windshear. AND SINCE the runway /performance is OK for 200,000 lbs, you will have enough runway to either GO or REJECT.

AS to other posts regarding callouts of V1 to be started at V1 minus 5 so as to be complete by V1, we really spoke enough about it. Calling V1 at V1 means the call will be complete AFTER V1 and therefore compromising the go , no go decision.

NOW if you really don't understand, you might want to get that book I mentioned.

OR if you are being obstinate that's fine too.

Indeed there are others who increase speed in a takeoff into supsected windshear and it is covered in the thread that is mentioned in post 13.

Go faster at takeoff means better chance at getting out of a windshear encounter. zoom zoom great silver bird goes into sky. comprende?

[glendalegoon]

http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC00-54.pdf

OK, here it is from the FAA. you can read the whole thing or go to takeoff precautions around page 30 (document, not computer).

go faster means better , get it? and excuse me if I didn't say it exactly the way the FAA does.

[Brian Abraham]

Unless?Unless what?

[de facto]

again folks, if your takeoff weight is max minus 20,000 lbs, you could use the max numbers and have more energy at liftoff and still the same protections as if you were at max takeoff weight for a given runway. Does your's have this?

Of course.
VR can be increased up to 20 kts and rotation delayed to the last 2000 ft.
From no one else than Mr Boeing himself.

[glendalegoon]

thanks defacto


I am too tired to carry on arguing. some argue for the sake of arguing.

over and out

and ADVISE TO AVOID

[Denti]

@Air Rabbit, we do not call out V1 anymore, the aircraft does it. However, the aircraft calls V1 at V1 minus two knots. For exactly the reasons you state. I know other operators use V1 - 3kts for "manual" call outs.

On the other hand Boeing advises improved climb speed schedules as those do increase the climb gradient quite a bit, which indeed does help in cases like for example windshear. Of course it is even better not to encounter any windshear, which is why we do have some restrictions on weather conditions that have a higher windshear risk, as well as predictive and reactive windshear warning systems (those should are the norm in todays aircraft).

We don't have the approval that de facto mentions, however the EFB software uses improved climb speeds as normal selection and we have to actively deselect them if we do not wish to use them (it is not fun to rotate at 180kts in HRG, the runway is awful). Of course we can always do a calculation with and without improved speeds and compare the results if we want to.

[de facto]

I have used the improved climb option as well :)
Denti,your SUPP procedure under windshear section does not mention the use of increasing speed of rotation -VR-by a max of 20?
To be clear the VR set on the 'bugs' is the VR for the actual weight.

[PEI_3721]

Apart from the AC being a little dated and originating from Boeing, it reflects a ‘can do’ attitude. How can we do this vice should we be doing this.
A significant weakness is shown in Fig 25 ‘model of flight crew actions’, where the decision ‘is it safe’ is judgemental and might assume that all of the preceding indications are available, or that they are sufficiently accurate to enable the selection of a safe course of action. And even if the situation is ‘safe’, then taking ‘precautions’ only need to be considered – another judgement. Furthermore, how likely is it that crews will recall all of the detailed advice and change in procedures according to the situation – which may have already been misjudged?

Should the judgement consider several ‘medium’ risks as being ‘high’?
In the example incident the indications were at best medium (perhaps only one hint); did the crew suffer an error of judgement, or was the situational information insufficient to judge? Note that the windshear conditions in that incident equated to FAA training #4, which is based on the DFW DC10 accident.

My rule is if you have to consider precautions then you should not be thinking of doing ‘it’ – ‘it’ is not safe enough.

[glendalegoon]

PEI

I can't remember a DFW DC10 windshear accident. Perhaps you meant the DFW L1011 accident?

[AirRabbit]

Glendalegoon / Denti

I truly don't desire to rekindle a long-winded exchange of what you think I don't know and my unsuccessful attempts to convince that I do ... so, please, just for a brief moment re-read what had been posted and then go back and re-read what V1 means ... and it doesn't mean that a decision is to be initiated at that point ... Rather it means that the ACTIONS resulting from the Go-No Go decision must have been initiated no later than that airspeed. "That" airspeed is V1 ... in this context we're not discussing V2. In that V2 is the takeoff safety speed, there very well be some room to delay rotation ... but that is a very different issue from delaying ALL of the "takeoff reference" speeds (which include V1, VR, and V2) because wind shear has been reported in the area.

I would never recommend doing something contrary to the approved company procedures - for ANY company ... but that doesn't preclude anyone from questioning what procedures are established by some upper level "company man" who just may have insufficient understanding of the factors involved - I'm not making accusations ... just pointing out potential issues.

[Denti]

It is not about company procedures, it is about physics. And of course the procedures to cover it are OEM procedures which are approved by the relevant aviation authority, not company procedures. In case of the automatic "V1" call it is actually a fix by the OEM to get rid of individual differences between the call and the computed speed.

Simply put, in my 737 i can comfortably take off in a pretty short distance. Everything is fine, i do use the minimum V1 for the conditions. However V1 is not a fixed speed, it is flexible within the constraints given by the environment (weather, runway, aircraft weight, configuration is flexible as well). Same as all other V speeds. With the minimum V speeds i might have excessive runway, basically runway that is not used and won't be used if i continue to use those speeds (in a close to V1 stop case i would stop well before the runway end, in a go case i would be several hundred feet above the runway end). I can now increase my V speeds, which only means i use more of the given runway, but not more than is available. All it does is gives me a longer time to reject a take off, which might come in handy in a windshear case, and more energy which can be converted in a better climb gradient. Another nice thing in a windshear.

Comparing non-improved and improved take off calculations show that it is usually a choice between being obstacle limited or field length limited.

[AirRabbit]

Thanks for the note Denti -
…and as long as the process is as you describe, a defined, analyzed, sifted, sorted, and selected procedure to provide alternatives for a given set of circumstances … I have absolutely NO problem with doing precisely that. It’s when I hear that that its “OK” to select a V1 speed 15-18 knots below the actual V1 speed so that the proper considerations can be made for an abort if required, I get more than a little warped. I’ve said on more than one occasion that a knot or 2 is likely to be too small an increment to get excited over – but under the circumstances and procedures you describe, particularly in reference to V2, I’ll sit down and continue reading. It’s when someone says that a longer runway allows them to “adjust the V speeds” by the kinds of numbers that were floating around OR when someone says that it takes an inordinate amount of time to SAY the words “Vee One,” I admit, I do get exercised. The fact is that V1 is the speed that is defined by the first action taken to initiate an abort if one was to be attempted – and beyond which any such abort should not be attempted. The pilot flying should not be sitting there admiring his/her takeoff roll, and when the other pilot sings out “V1” the pilot flying then decides whether or not to continue the takeoff. And it seems as though at least some here were operating on that understanding! Unless it is adjusted due to the length of the runway, or some other meaningful, examined, and preferably charted value, the callout at V1 is the signal that no abort should be initiated from then on.