Windshear precautions (Airline pilots please comment).

BeechBoy

BeechBoy

New Member
Does anyone have good advice on takeoff and landing strategies when windshear is suspected? Obviously we're going to avoid known severe windshear but there are days when LLWS advisories are in effect when we're going to continue operating.

Here's some words of wisdom I've gathered thus far. I'd welcome anyone's comments on them.

TAKEOFF:

1. Advisory Circular 00-54 recommends increasing V2 by using the following technique: Determine your maximum allowable weight for the selected runway using the lowest flap setting. "Pretend" your airplane weighs this much and use a V2 for this higher weight. Rotate and climb out normally. AC 00-54 specifically states not to lower the nose once airborne to gain additional airspeed.

2. "Fly The Wing" recommends the same thing but he adds an extra 25 knots to the increased Vr and then adds ANOTHER 25 knots by lowering the nose once airborne. (This last step is confusing to me because he states earlier in his book that he NEVER does this. Plus the fact that AC 00-54 also says not to do this). Of course your rotation speed is going to be WAY up there and tire limit speed may become an issue. (Why not just simplify this and rotate at tire limit speed or when 2000 feet of runway is left, whichever comes first? The goal seems to be to get airborne at the max speed possible so why not just go for broke?)


LANDING:

1. AC 00-54 says to add up to 20 knots on the approach and carry this extra airspeed into the flare. (My observation: if you carry an extra 20 knots into the flare in a jet you're going to be lucky to touch down on the runway - much less in the touchdown zone).

2. "Fly The Wing" says to determine your maximum landing weight (with minimum flap setting) for the runway to be used and, once again, pretend you're at this higher weight and use it to determine Vref. Now add an EXTRA 20 knots to this. (Once again this seems VERY fast. Yeah, your well protected against windshear but winning the windshear "battle" only to lose the "war" by rolling off the end of the runway doesn't sound like a winning strategy).

Anyone ever use these techniques in real life or in a sim?
 
This may go without saying, BUT, try to avoid take offs or landings during windshear, BUT if you must, what you stated was, as I far as I have seen, a fairly common practice.

Using the max weight speeds (V2, Vref, etc) for a paticular runway gives you the benefit of knowing you will have the runway required and the extra margin of airspeed if you should need it. The adding of 20/25 knots to those already increased speeds, not so sure about. +25 to a "heavy" V2, not too hard to do, but plus 20 knots to a "heavy" Vref, you could run out of runway real quick. The DC8's landing role was increased about 110 feet per knot over Vref.

Sumpin to consider.
 
Beechboy, you guys don't practice this in the sim? We practice it everytimg during pcs, newhire and upgrade training

Windshear is one of those things that I hope to NEVER be in.

AVOID IT

Basically, our procedure is to add power, up to firewalling the engines and climb out at 15-30 degrees nose up in the configuration you are in. A fully loaded Beech 1900 on a hot humid day with the same scenario that brought down the Delta L1011 in DFW will climb out at 150 with 4000 pounds of torque. Really don't have time to sit there and worry about your weight, figure out what EXACT speed to be at. Let the PT6 engines get you out of it. God forbid if I am in that situation, I don't care if I have to firewall the engine to get me out of it. I'll let the mechanics worry about overhalling them once I land.
 
We practice windshear RECOVERY in the sim but we were never given any procedure to stack the odds in our favor BEFORE flying into an area of suspected windshear.

The airspeeds I mentioned are not targets to use if severe windshear is encountered. Rather they are "higher than normal" airspeeds to be used as you approached the shear area. Once windshear is encountered airspeed is not a consideration. We apply max power and pitch up 15 degrees (respecting the shaker).

Obviously, the higher airspeed you have when you encounter the shear the better off you're going to be. The only concern are the tradeoffs (in particular, trying to land an airplane where you're carrying considerable airspeed over Vref).

What I really want to know is what is the best way to stack the odds in my favor before flying into an area of suspected windshear. I'd like to reiterate that this isn't something to be used to penetrate known severe windshear (that's when I stay on the ground). I'm talking about a procedure to use when windshear advisories are in effect.
 
The KC-135 had a procedure for windshear recovery that was similar to the one above, but we also had a procedure for takeoffs and landings into known windshear conditions.

The procedures were listed as "use only if necessary", of course, but they worked like this:

TAKEOFF- for T/O first you need to figure out if it's a performance INCREASING windshear, or a performance decreasing windshear. A performance increasing windshear is one where the headwind will increase, or the tailwind will decrease as you go through it on the way up. This is performance increasing, because your indicated airspeed will momentarily increase (as well as climb performance) and is generally not that dangerous. So for performance increasing, we didn't really worry about it.

PERFORMANCE DECREASING WINDSHEAR (Take-off)- Our T.O. didn't define it as "severe" windshear until it was greater than 15 knots of decrease (or in other words the headwind gets smaller suddenly by 15 knots, or the tailwind suddenly gets bigger by 15 knots.) Then, our procedure was simple. We increased our rotate and climb out speeds by the amount of the windshear, essentially assuming those extra 15 or more knots were going to go away on the climb and we'd be back "on speed" after we hit the shear. I think there was a limit of how much we could increase, though, but I don't remember it exactly off the top of my head. I want to say you could increase by 25 knots or up to tire placard speed, whichever came first.

PERFORMANCE INCREASING WINDSHEAR (Landing) - Again, since it was performance increasing, we didn't have any procedures to apply. All we had was a sketch warning us that as we went through it and our airspeed increased suddenly, not to pull the power to compensate because it could result in an overcorrection.

PERFORMANCE DECREASING WINDSHEAR (Landing) - In this scenario we computed something called Vmgs, which was Min Ground Speed (and actually, we computed it prior to EVERY approach, but we would only use it if we suspected wind shear). Here's how it was computed. You basically take your Vref, or Vapproach, or whatever they call the speed that you are going to be flying on short final and convert it to a ground speed based on the winds that they are calling over the tower freq. This is your Vmgs. THIS IS VERY IMPORTANT--DON'T USE THE COMPUTED WINDS THAT THE AIRPLANE IS SHOWING OFF THE GPS, BECAUSE THESE COME IN LATER. Ok, so now you know what groundspeed the airplane should be flying on final at Vref/Vapproach/Vwhatever. Now you look at your ACTUAL groundspeed on the approach when you are "on speed", (so obviously you need a groundspeed readout from an FMS or a GPS to use the technique). If the groundspeed you show is less than the Vmgs, the difference is the amount of airspeed you could loose going through a shear. So just increase your Vref or whatever by this amount, and that way, when you go through the shear you come out the other side of it "on speed". Again, there is a limit as to how much adjustment you could make before common sense kicks in and you just decide to initiate a go around. I think the limit for us on landing was 20 knots, or basically if we needed to fly 20 knots fast on final to make our actual groundspeed equal our Vmgs we were allowed to continue, but if we had to fly 21 knots fast we weren't allowed to continue the approach. Once again, I don't fly that airplane anymore so the actual numbers have gotten a little fuzzy, but that's how the concepts worked.
 
BeechBoy said:
I'm talking about a procedure to use when windshear advisories are in effect.
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you need to find out what other aircraft have been reporting. If someone tells tower +/- 5 kts on approach that may be all it takes for LLWS ADVZY's to start showing up in the ATIS. It really doesnt tell you if its +/-5 or you can be expecting a 20 kt gain @ 500 ft or a 15 kt loss @ 100 ft, etc.

If something like +/- 10 kts is being reported i'll fly my adjusted speeds (adjusted for weight and gust factor, etc) as best i can. We have trend vectors on the airspeed so that helps a bit. If i'm anticipating a big loss of airspeed i'll carry some extra speed and perhaps select a different setting for landing flaps, and be back down to ref before i land. If i'm anticipating a gain i'll fly my speeds and deal with it. Usually though the best 'report' you are going to get is +/- 10 reported by all aircraft, or something to that effect.

Now with that said this is for dealing with light shear. If the airspeed gets down to the low speed awareness area, even hints at the shaker, shoots through max flap speed or the box gives us the "WINDSHEAR" aural, i'm out of there.
 
Well no "flex" takeoffs for sure (reduced thrust takeoffs used most of the time on longer runways to be nice to the engines), Continuous ignition ON, I will leave the APU on to keep all the power coming out of the engines instead of taking some off the bleeds, and if crap hits the fan (ground contact eminent) I am flipping the Engine control switches off auto (now in manual mode)- LOTS more go power but you will exceed limitations- I DONT CARE! As long as I am alive! Thats my approach to it if the worst arrives. Like everyone else has said- AVOID IT! I have dealt with a 15knot shear so far about 100ft off the ground (in takeoff)- flew the FD and it all worked out, got my adrenaline going though seeing the Windshear message come up on the FD!
 
Some things we do at Southernjets.

Takeoff: Compute an increased VR based upon the MAX runway allowable takeoff weight. IE you might only be 290,000 lbs on takeoff, but if the RATOW is 405,000 lbs, look in the charts, use 405,000 and determine what an adjusted "reference only" VR would be. Also, if you encounter windshear, extend the takeoff roll until the last 2000 feet or so. That figure might not be correct, I can't remember.

There's no much we do on arrival beyond adjusting the final approach speed. (1/2 the stead state HW component plus ALL of the gust).
 
Doug Taylor said:
Some things we do at Southernjets.

Takeoff: Compute an increased VR based upon the MAX runway allowable takeoff weight. IE you might only be 290,000 lbs on takeoff, but if the RATOW is 405,000 lbs, look in the charts, use 405,000 and determine what an adjusted "reference only" VR would be. Also, if you encounter windshear, extend the takeoff roll until the last 2000 feet or so. That figure might not be correct, I can't remember.

There's no much we do on arrival beyond adjusting the final approach speed. (1/2 the stead state HW component plus ALL of the gust).
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Standard from the AC, rotate at the performance limited Vr or the last 2000', which ever occurs first.
 
One thing to add, on a wind shear encounter on landing requiring a go around we don't do any configuration changes until out of the shear.
 
Doug Taylor said:
Some things we do at Southernjets.

Takeoff: Compute an increased VR based upon the MAX runway allowable takeoff weight. IE you might only be 290,000 lbs on takeoff, but if the RATOW is 405,000 lbs, look in the charts, use 405,000 and determine what an adjusted "reference only" VR would be. Also, if you encounter windshear, extend the takeoff roll until the last 2000 feet or so. That figure might not be correct, I can't remember.

There's no much we do on arrival beyond adjusting the final approach speed. (1/2 the stead state HW component plus ALL of the gust).
Click to expand...

Good Answer, Good Answer.

On landing one also needs to consider spool time of the engines. In windshear conditions we try to keep the engines spooled up as much as possible. If they get to the idle ranges it can take the JT8D 5-7 seconds to begin producing power. Not a fun feeling when all you can do is wait after pushing the thrust levers foward?

BTW Doug, how fast do the 75/767 engines spool up?
 
Doug Taylor said:
There's no much we do on arrival beyond adjusting the final approach speed. (1/2 the stead state HW component plus ALL of the gust).
Click to expand...

Do you carry this all the way to the flare? In the Beech, carrying extra airspeed into the flare isn't a big deal. In a jet I imagine you'd have to just "drive it on" to the runway and then get busy with brakes and reverse. Is this correct?

By the way, thanks everyone for your comments. Much appreciated.
 
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