Negative wind shear

[Ed Cesnalis]

My last flight, home to Mammoth From Los Angeles ended with a negative wind shear landing.  I have a few dozen NWS landings in the CTSW now mostly at Mammoth Yosemite and a couple at South Lake Tahoe. Here's my method:

• 15° flaps
• Approach speed 60-70kts
• Overfly first half of runway to get a feel for the conditions
• Adopt landing attitude 
• Large throttle adjustments to maintain speed and attitude
• Keep stick centered ( fore/aft ) with trim neutral or nose down
• When shear is negative use it for vertical speed to sink to runway
• Just before contact arrest vertical speed with a quick move of stick to aft stop
• If there isn't enough stab to arrest sink use throttle.

Leaving the stick centered saves a lot of kinetic energy to use for a soft contact.  A couple of times I had to add full power as well but most of the time I only need stick even though it looks like its going to be a hard contact.

 

Final step is to fly the plane on roll-out and be ready to take off again if I can't maintain the runway.

 

I had more trouble with my crosswind landing in Van Nuys it was gusty and I'm not used to being gusted by such dense sea level air.  Powerful gusts but far more smooth and predictable than high mountain winds.

 

I mostly land in these conditions when coming home from a cross country.  I am reluctant to land in them for a video.

 

This video demonstrates the feeling well, with the long lens I see the jets doing the same thing, maintaining attitude and speed resulting in rapid sink instead of a normal glide path.

 

[Duane Jefts]

Policy at the two airlines I flew for was, if windshear detected, go around!

 

I always thought that was a good idea.

[Ed Cesnalis]

The Alaska Air pilots that come in here flying Q400s complain about the shear a lot while United flying Jets seem ok.  We can have negative wind shear all day long for days at a time.

[WmInce]

Just what is "negative" wind shear?

What distinguishes it?

I am unfamiliar with that term.

 

I am familiar with increasing performance or decreasing performance wind shear phenomena.

[WmInce]

Policy at the two airlines I flew for was, if windshear detected, go around! I always thought that was a good idea.

Concur.

Mandatory go around followed by a PIREP.

[Ed Cesnalis]

Just what is "negative" wind shear?

What distinguishes it?

I am unfamiliar with that term.

 

I am familiar with increasing performance or decreasing performance wind shear phenomena.

 

Negative wind shear is decreasing performance.  It could be a simple decrease in headwind component or at our field it could be a change from headwind to tailwind.  When the crosswind is close to 90 degrees and the direction is variable you have a good setup for tailwind.

[WmInce]

The training I received emphasized that, generally, wind shear is characterized by an initial increase in performance (airspeed increase), followed by a pronounced downdraft and then a decrease in performance (loss of airspeed), commensurate with the airspeed increase at the beginning.

[Ed Cesnalis]

The training I received emphasized that, generally, wind shear is characterized by an initial increase in performance (airspeed increase), followed by a pronounced downdraft and then a decrease in performance (loss of airspeed), commensurate with the airspeed increase at the beginning.

 

I think that is a description of encountering positive wind shear with a downdraft thrown in.  You can encounter negative shear even very near the ground where downdrafts can't happen.

 

Negative would initially be a decrease in performance followed by and increase.

[FastEddieB]

I also had never heard the term.

 

I would assume that "positive" windshear occurs when the shear results in increased airspeed, and "negative" results in decreased airspeed. Both as a result of momentarily increased or decreased headwind or tailwind component.

 

Correct?

[FlyingMonkey]

Tower:  "Caution, negative windshear."

 

Pilot:  "No windshear, I'm landing!"  

 

[Ed Cesnalis]

I also had never heard the term.

 

I would assume that "positive" windshear occurs when the shear results in increased airspeed, and "negative" results in decreased airspeed. Both as a result of momentarily increased or decreased headwind or tailwind component.

 

Correct?

 

That's correct for a simple transition from 1 wind to another with the shear being at the transition.  After the transition your speed normalizes because wind does not effect airspeed but wind shear does.

 

When we get a lot of cross wind in the runway environment our local terrain creates many rotors and many distinct winds.  In these cases speed may never normalize instead you encounter more shear.  Have you ever landed with a big wind at pattern altitude and near calm at the ground?  In that case, the shear or gradient should have layers and every step down decreases performance.

[Runtoeat]

Your conditions sound really difficult.  Must be tense with one hand on the stick and one on the throttle and feet dancing on the pedals.  I might end up being in one of those pictures you see where someone crawling out from a CT that's laying on it's roof.  Interesting comments on higher density crosswinds at lower altitude.  Hadn't thought about less effect at altitude due to this.

[Ed Cesnalis]

Roofs don't usually come off when we have 100mph winds, above that they do.  The lower density is quite noticeable.

 

I have seen a few other CTs here over the years but never when it was big.  I did fly an instructor from FD west into here on a big day and he flew my CT back to Carson City.  I remember the landing had big sink at mid field from 100'agl that resulted in a soft contact.  He took it all in stride and did a fine job on the take-off.  Once you get 50 miles from Mammoth conditions smooth out.

 

You would do fine because you recognize the potential, they people that can't hold the runway are usually not even aware until its too late.

 

Spring is here, that's when the fun begins, windy spring conditions are not here yet.

[GravityKnight]

 

 

Spring is here, that's when the fun begins, windy spring conditions are not here yet.

 

I hear you. Spring where I am is insane as well. 60 knot gusting winds, can come from any direction. Windsock dancing in circles, violent up and down drafts. Hail, snow, rain. About two weeks ago, we had an entire week where I didn't see the wind drop below 30 knots.. mostly 45-55 knots all day, all night, days worth flying are few and far between this time of year.... Being next to the mountains definitely causes some interesting weather...