Windshear on T.O

[uwochris]

Hey guys,

Why is it recommended that if there is windshear on takeoff, you should use a high pitch attitude close to "stick shaker"? To me this seems unsafe- ie) you'd be close to stall, and if there is windshear, the risk of stalling is high.

Thanks in advance.

 

[flatspin7]

The risk of slamming back into the ground is greater.... A severe windshear encounter is an emergency situation that you must use every ounce of the aircrafts performance to stuggle out of it. If you get stuck in a 3000-4000+ Foot Per Minute down draft you really dont have any choice but to get that nose up and ride the shaker to get every thing possible out of the aircraft.

 

[Dangerkitty]

The risk of slamming back into the ground is greater.... A severe windshear encounter is an emergency situation that you must use every ounce of the aircrafts performance to stuggle out of it. If you get stuck in a 3000-4000+ Foot Per Minute down draft you really dont have any choice but to get that nose up and ride the shaker to get every thing possible out of the aircraft.

I was taught and agreed with your above statement until I got my type rating in the Falcon 50EX.

At both Continental Express and American Airlines we were taught the standard pull up and hold it till the shaker starts. I thought that was the gosphel in regards to Windshear until I went to Falcon school.

Dassault sees it a little differently. They suggest that you keep your nose level with the horizon and try to get out of the windshear as fast as possible. At first I thought that they were nuts but then I tried it in the sim and it works really well. If you are pitched up say 20 degrees and flying 130 knots across the ground it will take you alot longer to get out of the windshear than if you are pitched closer to the horizon but going 250 knots across the ground. You might be losing quite a bit more altitude but again you will fly out of the shear faster.

The theory is the same as what I do when I am flying my glider. When I am in very very nice lift I fly L/D, 1 knot above a stall to maximize my exposure to the lift in the thermal. HOWEVER, when I am in heavy sink I fly as fast as I can to get out of it.

Like I said I thought those folks at Dassault and Flightsafety were nuts but after doing it in the sim I am beginning to question if pulling up to the shaker is always the best way to escape.

Not saying one is better than the other just thought I would bring this into the discussion.

 

[Flying Illini]

I've heard the above, about flying fast to get out of the shear...but IMO, it is better to fly the shaker. You just don't know how fast the shear is sending you downhill nor do you know how big the area of the downdraft is, and if you are just after T/O, you are less than 1000' AGL and you need every foot you can get. Putting the nose down might work better if you have some altitude to work with, but close to the ground, pitch up and maximize your aircraft's performance.

 

[gfvalvo]

If you get stuck in a 3000-4000+ Foot Per Minute down draft

Wow, at 3000 or 4000 FPM in the PA32 or M20J that I fly I guess it doesn't matter. Dirt sandwich for me.

 

[Phony Marconi]

I understand why you are confused as to windshear escape maneuvers which dictate flying to the stickshaker. However, I can shed some light:

The obstacle-avoidance procedure we learn in primary training is to fly at best-gradient-of-climb (Vx) to climb at the steepest possible angle. So it would seem that to avoid hitting obstacles, Vx would be the best airspeed. It is not.

If a pilot maintains Vx, that will yield the best possible gradient when compared with maintaining any other speed. But a pilot who pitches up and decelerates through Vx and continues to decelerate will climb at an even steeper gradient. The concept of Vx only applies to a steady airspeed. A decelerating pitch angle will exchange airspeed for altitude while the airplane decelerates.

Thus a plane encountering windshear can exchange all available energy for altitude by pitching up to the 'shaker, thus exchanging all available airspeed for altitude.

 

[uwochris]

Thanks for all the replies!

Should pilots, however,not be conscerned about encountering a strong updraft at such a nose-high attitude, that a stall could result?

 

[avbug]

The primary area of concern is a microburst encounter, and this can be avoided by not taking off under or close to a thunderstorm, or approaching to land near the same.

In some locals, dry airmass thunderstorms or dry microbursts can occur without the traditional appearance of a thunderstorm.

Blindly pitching to the stall warning or stick shaker is the wrong choice, but pitching with power to avoid ground contact is the right choice.

Don't get any slower than you need to as you cross the region of greatest vertical gusts. How much you need to pitch and how long you need to hold it depends entirely on the nature of what you encounter. You may not have the capability of flying level to get out of it...but you may.

I've encountered a microburst both on landing, and on takeoff, that required continuously pitching to avoid ground contact, and then not by much. In other cases, particularly in rapidly changing conditions in mountainous areas, I've encountered microbursts or descending air which permitted a rapid transit without an uncomfortable loss of performance.

Deal with what you get at the time with what you must, sacrificing no more airspeed or altitude than you absolutely must. Don't forget, you're going to wind up on the downwind side of it, and arriving there low, slow, already far behind the power curve, and out of ideas, is not the best place to be.

 

[MauleSkinner]

Blindly pitching to the stall warning or stick shaker is the wrong choice, but pitching with power to avoid ground contact is the right choice.

I agree...I had this discussion with the my last couple of sim instructors. One said I should go right to the shaker as soon as I encountered the downburst, the other saw what I was doing and approved to start with.

My position was that I didn't want to trade all my airspeed for climb too early. If I used up all my energy at 500 feet, I'd just accelerate towards the ground on the shaker, and if I hit the ground I'd hit hard. On the other hand, if I maintain some speed until I'm closer to the ground, and find impact unavoidable, I can make my energy trade so as to minimize my descent rate when I hit.

If impact is inevitable, I want to hit as softly as possible

Fly safe!

David

 

[Say Again Over]

Dassault sees it a little differently

Unless you are an experienced test pilot I would recommend following the manufacturers procedures