Micro burst/downdraft & Flaps

[AdamZ]

Today AOPA's e-training bulletin discussed Spring Thunderstorms and related issues such as micro bursts an down drafts. One thing it discussed was procedure in a burst when landing configuration. It says full power retract gear and flaps. :

Questions:

1) Would one pancake in to the ground in the out bound side of a burst because you loose lift due to loss of airspeed or are you literally pushed down from above like a hand holding you down and lift is lost that way.

2) Would say, one notch of flaps with full power assist with a bit more lift? I know drag would increase possibly keeping you in the burst longer but with only one notch the the added lift would be far greater than the drag created?

3) Wouldn't retracting all flaps in downdraft dump even more lift if you were close to the ground? I suppose that the time to retract the flaps would be on the up wind side of the burst.

4) If you find your self running into the upwind side of a burst is your best bet to fly out the other side or reverse course. Logic would tell you a course reversal or lateral exit would still subject you to the downward forces?

 

[Skip Miller]

Questions:

1) Would one pancake in to the ground in the out bound side of a burst because you loose lift due to loss of airspeed or are you literally pushed down from above like a hand holding you down and lift is lost that way.

You are literally pushed down. Large airplanes such as airliners have enough inertia that when the airspeed suddenly decreases in a microburst, the inertia of the plane prevents a rapid increase of airspeed. So the airliners sink for both being pushed down in the microburst and because of the loss of airspeed on the outbound side. This is of course compounded if the pilot reduced throttle during the period of increased airspeed, and now has to wait for the turbines to spool up again. A double whammy for them. But GA planes don't have that much inertia and will regain the airspeed rather quickly.

2) Would say, one notch of flaps with full power assist with a bit more lift? I know drag would increase possibly keeping you in the burst longer but with only one notch the the added lift would be far greater than the drag created?

Do you use one notch of flap to fly Vy? Why do something different than the POH listed configuration for maximum rate of climb?

3) Wouldn't retracting all flaps in downdraft dump even more lift if you were close to the ground? I suppose that the time to retract the flaps would be on the up wind side of the burst.

Retracting all flaps dumps lift wherever you are. But see the answer to #2. If the problem occurs so close to the ground that dumping the flaps will put you in contact with the ground, you are in deep doodoo already.

4) If you find your self running into the upwind side of a burst is your best bet to fly out the other side or reverse course. Logic would tell you a course reversal or lateral exit would still subject you to the downward forces?

That all depends on the size of the microburst, and the characteristics of the plane you are in. There can't be a one size fits all answer here.

All these are IMHO and others may disagree. What the bleep are you doing flying in microburst-likely weather anyhow?

-Skip

 

[Greg Bockelman]

Today AOPA's e-training bulletin discussed Spring Thunderstorms and related issues such as micro bursts an down drafts. One thing it discussed was procedure in a burst when landing configuration. It says full power retract gear and flaps. :

I'm not real sure about light aircraft, but the airlines teach to maintain current configuration with max thrust. Could be becaue they have a bunch of thrust available.

Questions:

1) Would one pancake in to the ground in the out bound side of a burst because you loose lift due to loss of airspeed or are you literally pushed down from above like a hand holding you down and lift is lost that way.

That is kind of a complicated question. You very seldom would get into the tailwind outflow of a microburst without having gone through the headwind outflow. As you approach a microburst, you would notice that you would have to decrease power and or pitch down to maintain glidepath and airspeed. Once you enter the downflow of the microburst, you will need full power and best climb airspeed to minimize altitude loss. As you enter the downflow, the airplane will want to pitch down to re establish airspeed. When you enter the outflow, the airplane is basically trying to regain the lost airspeed. So it will still want to pitch down. If you are low enough on the downwind outflow portion of the microburst, inertia plus the loss of lift will take you into the ground. If that looks iminant, it is best to do so at the slowest possible speed. It's easier to do with an airplane with a lot of inertia.

2) Would say, one notch of flaps with full power assist with a bit more lift? I know drag would increase possibly keeping you in the burst longer but with only one notch the the added lift would be far greater than the drag created?

I would think so.

3) Wouldn't retracting all flaps in downdraft dump even more lift if you were close to the ground? I suppose that the time to retract the flaps would be on the up wind side of the burst.

It's not something I would advocate doing. And you are right. The best time to do all that is on the upwind side.

4) If you find your self running into the upwind side of a burst is your best bet to fly out the other side or reverse course. Logic would tell you a course reversal or lateral exit would still subject you to the downward forces?

Reality is by the time you realize you are in a microburst, you are better off pushing on through.

Greg

 

[Greg Bockelman]

You are literally pushed down.

That is about right in simple terms. The physics of it are a little more complicated than that.

This is of course compounded if the pilot reduced throttle during the period of increased airspeed, and now has to wait for the turbines to spool up again.

I would hope that no major airline trained pilot would be at idle thrust on the downwind side of a microburst. We are trained in micro burst escape procedures and are aware of the signs of an imminent microburst entry. First thing we do is apply max thrust.

 

[poadeleted20]

1) Would one pancake in to the ground in the out bound side of a burst because you loose lift due to loss of airspeed or are you literally pushed down from above like a hand holding you down and lift is lost that way.

You will not see this "loss of airspeed" in the light planes most of us are flying. That phenomenon is a function of the sectional density of the aircraft, and ours is more like a leaf than a rock. Imagine dropping a rock and a leaf into a running stream -- which is carried along (i.e., keeps its relative speed to the fluid it is in -- zero lateral in both air and water) and which keeps going straight down (i.e., takes a while to be caught up in the new fluid stream)?

2) Would say, one notch of flaps with full power assist with a bit more lift? I know drag would increase possibly keeping you in the burst longer but with only one notch the the added lift would be far greater than the drag created?

Only if your plane has a better climb rate with one notch of flaps.

3) Wouldn't retracting all flaps in downdraft dump even more lift if you were close to the ground? I suppose that the time to retract the flaps would be on the up wind side of the burst.

It could, but not if you rotate to the proper AOA for Vy. Keep in mind that the sink experienced when retracting flaps is usually due to the pilot's failure to compensate for the changed effective incidence angle with flap retraction (watch the trailing edge move up and imagine the changing angle of the chord line reducing the AOA).

4) If you find your self running into the upwind side of a burst is your best bet to fly out the other side or reverse course. Logic would tell you a course reversal or lateral exit would still subject you to the downward forces?

If you don't fly under thunderstorm cells, you won't have this problem. However, the big issue for us light plane drivers is much more the problem of overcoming the downdraft in the middle (relatively low power-to-weight ratio)than dealing with sink due to loss of airspeed on the far side (relatively low weight to surface area ratio).

 

[Fast n' Furious]

Here's what FlightSafety is teaching for the King Air and Learjet families of airplanes regardless of your position in the microburst. Maximum allowable power (to include any transient power setting which in my case is 156% torque) and pitch to the stall warning/stick shaker. No configuration change until clear of the condition then cleanup the airplane via the missed approach/balked landing check. If anyone here takes regular sim training and the DFW L1011, or Charlotte DC9 scenarios are available to you, give them a try. Very scary but good training.

 

[Dave Siciliano]

Adam:

I hope the only time you're flying in conditions which could produce a strong micro burst is unforecast conditions where a new storm has quickly popped up. These are normally associated with pretty strong storm systems; most of the time smaller GA aircraft shouldn't be dealing with them.

If one didn't have on board weather or a storm scope, they could wander into conditions that could produce one of these. But, you'd normally get a CONVECTIVE SIGMET warning over the area, and if in those conditions, should be listening for updated weather. I could see a GA guy circumnavigating cells in summer afternoon conditions getting caught in something like this, but it usually takes a pretty substantial system to produce big enough downdrafts to be of concern. When I've arrived in an area where storms like this are occurring, approach is usually vectoring traffic around cells and things are pretty hectic.

The Delta flight that cratered here at D/FW followed another aircraft that reported strong downdrafts. If I was in a GA aircraft behind and airliner that reported strong downdrafts, I'd sure be trying finding another place to land if there was any other option. Another thing to do would be to increase your approach speed if possible (assuming you know about the possibility of such conditions when the approach begins).

I've gotten a strong downdraft on short final in Charlottesville on a clear day. Since then, I fly my approach a little faster and come in just a little steeper when there is a long runway and winds are high.

Best,

Dave

 

[Henning]

Today AOPA's e-training bulletin discussed Spring Thunderstorms and related issues such as micro bursts an down drafts. One thing it discussed was procedure in a burst when landing configuration. It says full power retract gear and flaps. :

Questions:

1) Would one pancake in to the ground in the out bound side of a burst because you loose lift due to loss of airspeed or are you literally pushed down from above like a hand holding you down and lift is lost that way.

2) Would say, one notch of flaps with full power assist with a bit more lift? I know drag would increase possibly keeping you in the burst longer but with only one notch the the added lift would be far greater than the drag created?

3) Wouldn't retracting all flaps in downdraft dump even more lift if you were close to the ground? I suppose that the time to retract the flaps would be on the up wind side of the burst.

4) If you find your self running into the upwind side of a burst is your best bet to fly out the other side or reverse course. Logic would tell you a course reversal or lateral exit would still subject you to the downward forces?

1) Both, it translates from down near the center of the burst to outward at the perifery.

2) Hard call to make, depends on the aircraft and conditions, you might want to play with the flaps as you're smooshing in to try and ease the hit.

3) Yes, and makes sense, only problem is, you might never see the upwind side of the burst. They can drop on you like a rock, it all depends on where you are relative to its core when it drops in.

4) Your best course of action will depend on your altitude, airspeed and capabilities. Don't forget, you best option may be to figure out the best place and attitude to crash. There is no guarantee that anything and everything you do will save you from impacting the deck. Sometime you just have to face that you're bite crap. Crash survival actions are not always the same as crash avoidance. Knowing when to switch from one mode to the other is crucial in these kinds of circumstances. Something many instructors don't cover is "Ok, Now that I'm f****d, how do I survive"