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What is a pilot taught to do, when a windshear is detected and the planes speed is above V1 and before Vr? I can't think of what is safer.

  • Rejecting, with the risk of overshooting the runway.
  • Taking off, with the risk of the windshear stalling the plane and dropping it on the ground. If the height of the aircraft was low it probably would just overshoot the runway. If the aircraft already gained some altitude, it could crash.

As well, are there any differences in procedures if the alert occured

  • After V1 but before Vr
  • After Vr
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    $\begingroup$ After Vr you would have already taken off. No chance of rejecting at that moment. $\endgroup$
    – vasin1987
    Oct 22 '17 at 10:37
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    $\begingroup$ What do you think V1 means? $\endgroup$
    – aaa90210
    Oct 23 '17 at 2:39
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V1 is the calculated decision point at which takeoff must continue. Unless the aircraft is suffering a catastrophic failure, the pilot should not abort takeoff after V1.

The danger when taking off during windshear is the sudden lost of airspeed may result in the airplane settling back on the ground after it has become airborne. The technique, therefore, is aimed at gaining ground clearance in the shortest amount of time possible. In general, this involves:

  • Apply max thrust
  • Delay rotation
  • Once rotation is initiated, quickly pitch up to gain altitude

Below is an extract from the Boeing 777 FCOM about taking off when windshear is suspected (my emphasis):

  • Takeoff with less than full rated thrust is not recommended (...)
  • Use the longest suitable runway (...)
  • Consider increasing Vr speed to the performance limited gross weight rotation speed. (...) 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.
  • (...) Minimize reductions from the initial climb pitch attitude until terrain and obstruction clearance is assured, unless stick shaker activates.
  • (...) Stick shaker must be respected at all times.
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What pilots are taught is that V1 is the go/no-go decision point. So after V1 they will continue with the take off, but the PIC is the final authority as to the operation of the flight and may take an action that he or she determines is best depending on the specific scenario.

Regarding Vr: pilots are trained to do thorough pre-flight planning and become familiar with the flight plan and weather conditions at the point of departure, route of flight, and destination at the calculated time of arrival. The pilots should know if there are windy weather conditions, an approaching front, or storm so that they can delay or cancel the flight or increase the Vr speed for takeoff from the standard Vr speed and have some extra buffer. That way if there is windshear they have a higher safety margin between their climb speed and stall speed.

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What I would do is to keep full throttle, and try to hold the plane in ground effect until reaching a fairly high speed. Then, start increasing altitude slowly and carefully...

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    $\begingroup$ But the question isn't what you would do; the question is what pilots are taught to do. $\endgroup$ Oct 22 '17 at 17:33
  • $\begingroup$ The question is (poorly) states both ways. Look at the title. $\endgroup$
    – Billy C.
    Oct 22 '17 at 19:58
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    $\begingroup$ If windshear occurs when the plane is slowly gaining altitude, the plane may drop back onto the runway hard, leading to structural damage and potentially loss of control. $\endgroup$
    – kevin
    Oct 22 '17 at 20:25
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    $\begingroup$ You're going to fly right into the hill/building at the end of the runway. $\endgroup$
    – user71659
    Oct 22 '17 at 20:53
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Windshear alert will not occur while on the ground on Airbuses; you will only get the alert once airborne, after Vr. I suspect most manufacturers have implemented a similar feature, perhaps, in order to prevent pilots from rejecting after V1.

What to do is usually a precise and exact procedure. While it does vary from type to type the main items are in common:

  • Use full available power
  • pitch up for a max rate of climb
  • maintain a/c configuration (no gear or flaps retract)
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In case of an engine failure, the total available thrust to the aircraft be reduced by 50% and it will lose at least 80% of the available climb thrust. Suffer wind shear in these conditions, the airplane may not be able to sustain a positive rate of climb on one engine, making it very dangerous at low levels. If low level wind shear conditions are anticipated at or in the vicinity of the airport, the pilot should consider this as part of the pre-takeoff briefing or postpone flight operations until conditions subside. Have a plan based upon the procedures listed in the AFM and stick with it. If an LLWAS alert is heard or if wind shear is encountered past V1, in general you’re past the point of no return and the airplane is going flying - unless you’re absolutely certain you can still stop it with the remaining runway available at your current takeoff weight, but that’s up to the captain to make that call. Most jets have a considerably higher OEI performance margin than do light or medium twins and would take a pretty strong wind shear in order to threaten climbout on OEI. Some things a pilot might do in those circumstances.

  • Advance both thrust levers to maximum.
  • Delay rotation or remain in ground effect until V2 has been attained. Accept additional touchdown on runway of airplane cannot sustain a climb until V2 is reached.
  • Select a Vr with an appropriate wind shear margin added on.
  • If sustained positive rate of climb is possible and attained, retract the gear to remove parasite drag.
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  • $\begingroup$ retracting the gear is exactelly the wrong move: think about it, if you are climbing steadly, then why get greedy and retract the gear? if you are not in a sustained climb, then why retract the gear at all? both cases it’s a wrong move, guaranteed to fail your checkride $\endgroup$
    – Radu094
    Oct 23 '17 at 8:16
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    $\begingroup$ Because you will get rid of the parasite drag faster and accelerate quicker to V2, allow for a greater rate of climb once you are maintaining V2 or flying at Vyse. And unless you have a manufacturer recommended OEI procedure saying otherwise, you will retract the landing gear once a positive rate is attained. Any examiner who would fail you for that is a moron who has no clue about flying multi engine aircraft. $\endgroup$ Oct 23 '17 at 8:57
  • $\begingroup$ seriously: retracting gear(or flaps) in windshear is a ‘fail-able offence’ :-) where I live in EASA-land .I understand it seems counterintuitive, I just always supposed that the action of ‘retracting’ the gear will create more drag initially with doors opening etc. I’ll look for the actual regs on this one tomorrow morning $\endgroup$
    – Radu094
    Oct 23 '17 at 17:41
  • $\begingroup$ No, the name of the game here is to get clear of the runway and obstacles as quickly as possible. Once you hit V1 1) you’re going flying at that point, so when Vr comes you will establish a pitch up appropriate to the aircraft type and depart. If wind shear is encountered at that point a pilot will ensure a positive and sustained rate of climb is indicated, then retract the gear. The last thing you need at that point is the gear hanging out of the airplane and impeding climb performance. You don’t need to divert extra climb thrust to fighting through the parasite drag of the gear. $\endgroup$ Oct 23 '17 at 19:28
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    $\begingroup$ @Radu094 Acceptable Means of Compliance and Guidance Material to Part-FCL, AMC1 FCL.930.MCCI, Part 3 point (b)(7), looks relevant, though not authoritative for what you're after. $\endgroup$
    – user
    Oct 23 '17 at 19:28

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