Microburst - Vy or pitch angle?

[rt4388]

At about the 9:30 mark in this video (link below) he says there should be no mention of airspeed if you encounter a microburst. He says you should just pitch for 15 degrees (or something applicable to your airplane). Anyone want to explain this to me? I don't quite understand why you wouldn't pitch for Vy and I feel like I'm missing something really simple. Would this be different for a GA aircraft compared to larger, commercial aircraft? Thanks!

 

[Cooter]

He explains it before the 9:30 point. He says kinetic energy is more important than potential energy. The idea is to have a positive VS while also gaining airspeed.

 

[Bill]

Several conflicting views when encountering sink. Some say Vy, some Vx, some say don't climb at all and use airspeed to fly out of the sink quicker.

 

[Fearless Tower]

In a microburst you are being driven into the ground. Airspeed means nothing to you at that point. Airspeed in that situation is like winning the lottery after you’ve been told you have terminal cancer.

You want full power and a pitch attitude that will get you out of it as quickly as possible.....before it fully drives you into the ground.

 

[unsafervguy]

That video is well worth 37minutes of your life.watch the whole thing.

 

[mscard88]

In a microburst you are being driven into the ground. Airspeed means nothing to you at that point. Airspeed in that situation is like winning the lottery after you’ve been told you have terminal cancer.

You want full power and a pitch attitude that will get you out of it as quickly as possible.....before it fully drives you into the ground.

This! Firewall it and pitch up to escape. Well, if all else fails you firewall it.

 

[Let'sgoflying!]

was taught 'pull to the stick shaker then relax it a bit'

 

[RyanB]

In a microburst you are being driven into the ground. Airspeed means nothing to you at that point. Airspeed in that situation is like winning the lottery after you’ve been told you have terminal cancer.

You want full power and a pitch attitude that will get you out of it as quickly as possible.....before it fully drives you into the ground.

This.

I’d also mention that microbursts are considered the black holes of aviation. Once you get caught up in one, it’s unlikely that any of our light aircraft will be able to power through them, but it all depends on the severity of it.

 

[Let'sgoflying!]

yep its basically a desperation maneuver.

 

[BillTIZ]

I’ve seen damage from microburst with outflow winds destroy light structures on the ground. Virga aloft on a hot day super cools the air, cold air is heavy and falls like a rock. Be careful flying under Virga.

 

[flyingcheesehead]

In a microburst you are being driven into the ground.

Yup... And if you want your vertical speed to be as low as possible when you hit the ground, you'll be at Vy.

However, you may be able to fly out of it by having a higher airspeed, and if you're still going into the ground, you'll have some extra energy available to arrest the descent at the very end.

Good luck - You're gonna need it.

 

[Kritchlow]

Follow the recommendations for your aircraft.
Honestly, if you’re caught in a *true* microburst in a small SE craft, not sure there’s much you can do after coming home to Jesus.

 

[35 AoA]

Most of ATP-CTP was not particularly new info for me, but the performance and upset recovery procedures for transport category aircraft were (at least as they apply to the esoteric realm of swept wing heavies, rather than the stubby wing fighters I am used to). What we were taught was basically just this. 20+ deg pitch is likely a departure for most. 15 is just shy of that. If you think about it in real terms, you are either going to hit the ground, or you are not during the microburst. If you depart the airplane, you are definitely going to hit the ground, provided you are already low enough to be immediately worried about a microburst event. If you don't depart the airplane, but buy yourself the most altitude above the ground in the process, you are at least living on borrowed time. Time with which, post microburst, you can apply other monkey skills to hopefully recover to a flyable sustainable airspeed and AoA to fly away. Just because you missed the ground during the microburst doesn't mean you won't have a handful of airplane to deal with afterwards, but you at least have a fighting chance of recovering. Vx climb is best sustained climb angle, which is certainly not the same thing as a zoom climb, but a zoom is the most altitude you can get in the shortest time with the energy you have left, which ultimately buys you options you otherwise wouldn't have had. Over to the 121 guys to correct and tear apart my elementary analysis, but that is what I walked away with. Like has been said, pitching down to gain some semblance of some V number to one day climb out with means nothing if you hit the ground trying to get there. Trade energy for altitude at the fastest rate possible without departing. For GA aircraft, you probably just don't have the KE or power to make it out, hence why there aren't really procedures that I am aware of (at least there weren't when I was doing 141 training 17 years ago).

 

[Stewartb]

In severe drafts I use Vx. I use the same target speed whether the draft is up or down.

 

[sourdough44]

So many variables on conditions, mainly intensity, flight regime, A/C type, energy state, and on. The outcome could also vary.

The standard answer is AVOIDANCE, I know, can be gray at times.

 

[flyingcheesehead]

Well, I decided to do some more research into this, as it's pretty interesting. I think it verifies my earlier thoughts, as well.

A Microburst is <= 2.5 statute miles in diameter and is normally more like a mile in diameter. Vertical speed can be up to -6,000 fpm. Typical shear is about 60 knots (ie +30 followed by -30) but can be up to 120 knots, and the outflow can be as low as 300 AGL or as high as 1000 AGL.

First of all, Vx is the wrong speed. As @35 AoA said, this is all pointless if we hit the ground before we're out of the burst. Vx is the best *angle* of climb and is slower in both airspeed and climb than Vy. That means that we'll be in the burst longer and thus have a higher chance of hitting the ground, AND we'll hit the ground harder if we run out of altitude, AND we'll be closer to the stall when the shear hits. Bad idea all around.

So, for a "typical" microburst - Let's call it 1nm in diameter, -3000 fpm, and 60-knot shear up to 500 AGL, let's look at a couple scenarios.

First, if I hit it at a low IFR cruise altitude, say 3000 AGL. Let's say I see it coming and can adjust my airspeed accordingly before I actually hit it. At cruise power and attitude I'm going to be going down at 3000 fpm, but I'll be through it in 20 seconds. I lose 1000 feet of altitude.

If I instead choose to use Vy, I'll only be going down at maybe 1800 fpm, but it'll take me a bit over 34 seconds to transition and I'll lose 1,029 feet. Not a huge difference, but keep in mind I also have less kinetic energy at that point.

Now, let's say this microburst is centered halfway down a typical ILS (3º glideslope, 5nm/1600 AGL FAF to runway). In my Mooney, I would be flying the approach pretty close to my Vy of 105 KIAS. I would be above the outflow to start with, so let's go with a GS of 105 as well. Everything's hunky-dory until I'm 3nm from the runway, when I encounter the downdraft portion at 960 AGL. With instantaneous reaction time and no engine spool-up, let's say I can maintain Vy, which would normally get me maybe 1200 fpm at gross and average temps. Now I'm going down at 1800 fpm, so in about 15 seconds I'll be low enough to get into the outflow too.

Then, it's going to get mighty interesting - I'll be descending into the outflow, but I'm only going to have about 1/16 of a mile where I'll get the headwind, which might give me a bit of a boost but will also lower my groundspeed. Let's call that a wash for the moment in terms of altitude, putting me at 2.5nm from the runway at 450 AGL. I'm going to get the shift into tailwind territory and probably get right onto the edge of a stall before the airspeed recovers. Since everything is in transition during this period, it's tough to say exactly where I'll end up, but it's pretty safe to say I'm going to lose probably an extra 250 feet or so relative to everything else that was already going on in the process of regaining the lost airspeed, so now I'm at 200 AGL with only about 7 seconds until ground contact. I'm not gonna make it out of the downdraft, and I hit the ground around about 2.2 miles short of the runway. Provided the terrain is relatively flat and obstacle-free, this can be survivable. 1800 fpm is pretty close to the vertical speed of a Cirrus under a chute, and a pull at the end can arrest both vertical and forward speed. Definitely gonna need some luck here.

Now, let's say I shoot the approach at cruise power. That should get me about 180 knots. Since I'm still on the glideslope, nothing changes in the first two miles. , Then, I hit the downdraft, still at 960 AGL, but with a lot more speed. Say I recognize the microburst for what it is, and I've already done this analysis (which is kind of why I'm doing it, actually), and I decide to ride it out, same attitude, same speed as I had on the glideslope. I'll be going down at 3960 fpm (the vertical speed of the ILS at that airspeed plus the microburst speed). In 7 seconds, I'll be entering the outflow at 500 AGL and 2.85 nm from the runway. I'll be slowed down and it'll take another 8.4 seconds to hit the center of the microburst, but I won't make it there - I already will have hit the ground.

So, I'm gonna hit the ground either way... Best thing I can do is to have enough energy to pull into a brief 3000 fpm "climb" relative to the air around me at just the moment I'm about to hit the ground. Yikes.

 

[ejensen]

Get out of it as fast as you can, Va 90 degrees to the wind

 

[Fearless Tower]

Get out of it as fast as you can, Va 90 degrees to the wind

That’s the key.

Think of a microburst like getting caught in rip current. In a rip current you don’t swim toward the shore. You swim 90 degrees to the current. You want to get out of the current as fast as you possibly can.

And if flying an airplane with auto-throttles, turn the damn things off. Auto throttles will kill you in a microburst.

 

[tspear]

How do you know 90 degrees will be out the quickest?

My weather knowledge is kinda shaky (ok not kinda, but is) around microburts. However I always thought they tended to occur near a front or a cell. Which means straight ahead, straight behind, or left or maybe right is the quickest way out.

Plus have you considered lost energy to turn?

Tim

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[Stewartb]

My experience with down drafts is they're bordered by updrafts of approximately equal intensity. The transition from one to the next is violent. Once you're in there's no comfortable way out. I want to be slow enough that the airplane survives the shear.

 

[Clip4]

What ever.

 

[Cooter]

I got caught in a severe downdraft once over the mountains. At full power, I was still coming down at 4000fpm. No amount of airmanship will Vx out of that. Flying through it is the best bet.

The AF taught 15° nose up with radar alt. call outs from the other seat. When at a certain altitude (I think 300’) we pulled to the AOA limiter.

 

[Skyrys62]

How do you know 90 degrees will be out the quickest?

I'm not sure the intent is to turn 90 deg, but to use as much speed as possible to get out of the area of the downdraft. It's just the same concept as swimming out of a rip tide, fastest possible method. Which happens to be 90 deg for a rip current.
Full power straight ahead is probably fastest way out of down draft.

 

[mscard88]

The AF taught 15° nose up with radar alt. call outs from the other seat. When at a certain altitude (I think 300’) we pulled to the AOA limiter.

Sounds similar to what we had at the airline. A yellow FD (caution I think) would appear and then a red one with a even higher pitch, maybe 15-20* I think. @jordane93 should know as he’s current in the jet.

 

[benyflyguy]

What ever.

I wonder what that looks like real time and not accelerated. Spooky nonetheless but can’t imagine a GA aircraft seeing that cloud formation and just go through it!! Jets go around these right?

 

[Tarheelpilot]

a true microburst in any GA aircraft creates an environment where escape maneuvers are academic.

 

[jordane93]

Sounds similar to what we had at the airline. A yellow FD (caution I think) would appear and then a red one with a even higher pitch, maybe 15-20* I think. @jordane93 should know as he’s current in the jet.

Windshear caution (yellow) is increasing performance and will not give you any escape guidance. The AMI will still populate though. Windshear warning (red) is decreasing performing and will automatically disconnect the AP and give you command bars on where to pitch for best performance.

 

[danhagan]

I got caught in a severe downdraft once over the mountains. At full power, I was still coming down at 4000fpm. No amount of airmanship will Vx out of that. Flying through it is the best bet.

The AF taught 15° nose up with radar alt. call outs from the other seat. When at a certain altitude (I think 300’) we pulled to the AOA limiter.

A lot of the stuff we get here in the mountains is mechanical and not microburst type, meaning it'll subside at 500 AGL if it's downwind from a ridge. Guadalupe Peak can throw mechanical TB down drafts nearly 50 miles on high wind days. You can check weather/winds on the peak in your METARs entering KGDP just like its an airport

 

[flyingcheesehead]

Get out of it as fast as you can, Va 90 degrees to the wind

The "wind" is going straight down above 500-1000 AGL, and closer to the ground it's going in many directions. Might as well make it a 180, you'd probably get out quicker. But if you get into the downdraft portion of the microburst, a turn is just as likely to keep you in it for longer, and you're giving up some all-important lift and energy. I wouldn't turn unless it was to head toward something softer and cheaper, because I'm gonna hit the ground (see analysis above).

 

[mtuomi]

And if flying an airplane with auto-throttles, turn the damn things off. Auto throttles will kill you in a microburst.

Wtf?
The first thing to do is you turn ON the autothrottles.
"windshear, TOGA".

And definitely no 90 degree turns. THOSE will kill you.

 

[Witmo]

Wtf?
The first thing to do is you turn ON the autothrottles.
"windshear, TOGA".

And definitely no 90 degree turns. THOSE will kill you.

Did you watch the video?

 

[Tarheelpilot]

Wtf?
The first thing to do is you turn ON the autothrottles.
"windshear, TOGA".

And definitely no 90 degree turns. THOSE will kill you.

I have only flown one aircraft with auto throttle. The guidance for wind shear ascape was all automation off, toga thrust and follow the pitch commands while respecting the shaker.

 

[ejensen]

The "wind" is going straight down above 500-1000 AGL, and closer to the ground it's going in many directions. Might as well make it a 180, you'd probably get out quicker. But if you get into the downdraft portion of the microburst, a turn is just as likely to keep you in it for longer, and you're giving up some all-important lift and energy. I wouldn't turn unless it was to head toward something softer and cheaper, because I'm gonna hit the ground (see analysis above).

Yep, lots more info needed. How close to the ground, can you see the extent of the event, and more. I used to fight a mountain wave and after awhile realized I was just spending more time in to. Probably doesn't apply as well to a burst.

 

[mtuomi]

I have only flown one aircraft with auto throttle. The guidance for wind shear ascape was all automation off, toga thrust and follow the pitch commands while respecting the shaker.

Toga thrust turns on the autothrottles.

The type rating I'm studying for right now, it's TOGA (which turns on the autothrottles and "firewalls them"), no configuration changes, and no turns. Pitch up all the way to shaker if required.

 

[Tarheelpilot]

Toga thrust turns on the autothrottles.

The type rating I'm studying for right now, it's TOGA (which turns on the autothrottles and "firewalls them"), no configuration changes, and no turns. Pitch up all the way to shaker if required.

Depends on the airplane. In some TOGA turns them off. That’s why jets require type ratings. So we know what to do in the specific type we are flying.

 

[Fearless Tower]

Wtf?
The first thing to do is you turn ON the autothrottles.
"windshear, TOGA".

And definitely no 90 degree turns. THOSE will kill you.

A/T works for the TOGA, BUT if you aren’t paying attention, where A/T will kill you is when the burst is causing you to speed up. If you aren’t aware of what the automation is doing, you can find yourself with the power pullled off when you need it already spooled up. Those couple of seconds can make a huge difference.

And the 90 degree comment wasn’t referring to turns. It was simply an analogy to rip current escape where you swim as fast as you can 90 degrees to the current.

 

[Fearless Tower]

Toga thrust turns on the autothrottles.

The type rating I'm studying for right now, it's TOGA (which turns on the autothrottles and "firewalls them"), no configuration changes, and no turns. Pitch up all the way to shaker if required.

That’s where the misunderstanding is. Im referring to flying near microburst activity. Turn the A/T off. Turn it on when you want to TOGA is fine, but don’t get yourself INTO a burst with the A/T already engaged.

 

[mtuomi]

That’s where the misunderstanding is. Im referring to flying near microburst activity. Turn the A/T off. Turn it on when you want to TOGA is fine, but don’t get yourself INTO a burst with the A/T already engaged.

Ah ok, I got you now.

 

[35 AoA]

Toga thrust turns on the autothrottles.

The type rating I'm studying for right now, it's TOGA (which turns on the autothrottles and "firewalls them"), no configuration changes, and no turns. Pitch up all the way to shaker if required.

Very similar to the training I just did in the 757 sim.....only difference being you hit the TOGA paddle on the throttles, and then click out of autothrottles as you manually firewall them. Hitting the TOGA paddle invokes the TOGA guidance mode of the flight director (or wind shear if there is a WS advisory), but then auto throttles are deselected after that happens. I'm probably botching the terminology and some of the systems specifics here, but that was the basic stick and throttles mechanics we were taught.

 

[tspear]

That’s where the misunderstanding is. Im referring to flying near microburst activity. Turn the A/T off. Turn it on when you want to TOGA is fine, but don’t get yourself INTO a burst with the A/T already engaged.

I did not follow why.

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