Getting Out of Severe Downdraft

[your_dreamguy]

The other day, a captain was talking about severe downdrafts. He stated that if you ever hit severe downdraft where max power and holding Vyse wasn't enough...pull up until you get the stall horn.
I disagreed with the captain. Since the downdraft is pushing the airplane toward the ground, you want the airplane at it's best climb speed relative to the ground, which would be Vx. Also, once you get below max L/D, the drag increases as you go slower. That would be the scenario if you pitched to stall speed.

Anyone else want to weigh in?

Look forward to your responses.

 

[Stifler's Mom]

Actually pitch up until the stall horn or stick shaker. Think about where the relative wind is coming from and do whatever it takes to avoid ground impact.

 

[2000flyer]

Don't know the procedure for a prop a/c but I would think it's the same.

We're trained to pull the nose up to the stick shaker and maintain that pitch until recovery or impact. Two thoughts here. One, you're making a maximum effort to fly out of the downburst. Two, if its unrecoverable, you're at nearly the slowest speed possible prior to impact. Also something to think about is aircraft configuration. We've been taught to NOT change the configuration until recovery. For example, changing flap position will cause a momentary sink that could cancel any positive climb you've attained. Same for the gear. Again, two thoughts on this. One, raising the gear, what happens? In most aircraft you get gear-well doors that open which increases drag. Granted, it's minimal but you need absolutely everything you've got so why make it worse? Second, should an impact be unavoidable, you're gear is already down.

Newer avionics platforms also give you some indication of max pitch on the PFD as a reference.

2000Flyer

 

[A Squared]

If it were a downdraft that you could expect to be in for a long time, you'd be right, VY would be a good strategey. If you were going to be in the downdraft for say another 5 minutes, and you couldn't maintain altitude at Vy, you're hosed, and pulling back to stall warning wouldn't gain you anything. That is not the scenario, though. The downdraft is not a steady state condition, and it is assumed to be very localized in nature. If you can't outclimb it at best rate, you're attempting to trade your remaining airspeed (between best rate and stall) for altitude in order to buy time to fly out of it.

 

[JediNein]

My instructors for mountain flying and citation courses recommend pitching to VA or max turbulence penetration speed. This is to minimize downdraft exposure time.

I've used VA in light aircraft twice. Once was in the Sierras at 5000' AGL descending ~5000 fpm with full power with no turbulence. Thirty more seconds and I'd be landing on the freeway. The other was in IMC in a valley, a violent shove about ~8000 fpm down that gave up at 300' AGL. It took a week to pull the seat cushion out of my a$$ after that one.

Fly SAFE!
Jedi Nein

 

[A Squared]

My instructors for mountain flying and citation courses recommend pitching to VA or max turbulence penetration speed. This is to minimize downdraft exposure time.

I've used VA in light aircraft twice. Once was in the Sierras at 5000' AGL descending ~5000 fpm with full power with no turbulence. Thirty more seconds and I'd be landing on the freeway. The other was in IMC in a valley, a violent shove about ~8000 fpm down that gave up at 300' AGL. It took a week to pull the seat cushion out of my a$$ after that one.

Fly SAFE!
Jedi Nein

Yeah, I guess that these suggestions should be qualified. Pitching for VA might be a good strategey if you were at cruise at altitude and encountered mountain wave action. The pitch for the stick shaker advice is for close to the ground, at low airspeed in takeoff or landing configuration.

Obviously if you pitched for VA when you were at 400 feet, VREF and configured for landing, you'd hit the ground even if there was no downdraft <g>

 

[milplt]

Vy or stick-shaker....First, Vx does not play a part in the recovery - Vx is the speed for the best climb gradient - to get higher over a shorter distance traveled over the ground. What you are looking for is the best climb rate (best climb over a time period), which is Vy. You are in a downdraft of some downward velocity (some ft per minute), and you need a climb rate of more feet per minute than the downdraft.

If Vy isn't cutting it, then every publication that I have read recommends flying out at stick-shaker, or just above stall speed. There is no reason to smack the ground with plenty of energy on the aircraft.

DC-10 procedures called for firewall power and flying out in-and-out of the stick shaker. The A-300/310 has a similar logic built into the flight director. It starts off by having you climb at your current airspeed if you can maintain a climb doing so. If you can't climb, it directs you to sacrifice speed in order to maintain level flight until you hit Vss (stick-shaker). Once you hit stick-shaker, it has you ride along at stick-shaker - climbing or staying level if you can, or descending if you can't.

Using Va or maneuvering speed assumes that you are prepared for the windshear and then you want as much energy on the aircraft if possible so you can zoom climb if required - trading excess knots for altitude, or absorb a sudden loss of airspeed. Taking off into suspected windshear in the A-300/310 involves calculating a higher Vr (rotate speed - sometimes as much as 25-35 knots more than usual) so that you have the excess energy in case you have a sudden loss of airspeed or a loss of vertical speed.

Landing into windshear, you add knots to your approach speed (up to 20 knots in the DC-10 and A-300/310) to maintain a reference groundspeed - the groundspeed that you would expect to cross the threshold with assuming the winds that tower is reporting on the ground. For example, your approach airspeed is 70 knots and tower is calling a wind of 10 knots down the runway. Your reference groundspeed is 60 knots. While on final at 700 feet and an airspeed of 70 knots, you look at your GPS and you see that your groundspeed is 40 knots. Somewhere between where you are and the runway, you can assume that you will lose 20 knots of headwind. It could happen gradually (and would be of no concern), or it could happen all at once and cause your airspeed to go from 70 to 50 knots indicated. To protect against that worst case, you would add speed to your indicated airspeed (up to some reasonable limit) to maintain your 60 knot groundspeed. If the wind changes gradually, you just lower your indicated airspeed (to no slower than your normal approach speed) to keep that reference groundspeed around 60. If it happens all at once, your airspeed would suddenly decrease from 90 knots (assuming you added 20 knots) to 70 knots - your normal approach airspeed. If you notice that your actual groundspeed is greater than your reference groundspeed even when at you normal approach airspeed, you can expect a loss of tailwind or an increase in headwind as you descend - not nearly as big a concern.

 

[FN FAL]

Yeah, I guess that these suggestions should be qualified. Pitching for VA might be a good strategey if you were at cruise at altitude and encountered mountain wave action. The pitch for the stick shaker advice is for close to the ground, at low airspeed in takeoff or landing configuration.

Obviously if you pitched for VA when you were at 400 feet, VREF and configured for landing, you'd hit the ground even if there was no downdraft <g>

In the plane I fly, pitching for VA would result in descending...even on non-turbulent day.

 

[Bryan D]

In the plane I fly, pitching for VA would result in descending...even on non-turbulent day.

Sheet! You don't know nothin' You take a Super Cub with a 250' drag inducing banner hooked to the back and fly behind 10-20 story buildings at 500' agl with a 25 kt wind coming over them. It's like riding a mechanical bull.

 

[Axel]

Depends on the downdraft. As the above discussion indicates, people are talking about both downdrafts at altitude and close to the ground; both downdrafts associated with mountain wave and with windshear. All downdrafts are temporary and/or localized and the goal, of course, is to prevent one from filling the pitot tubes with dirt.

When ground contact is less of a factor, Vy will minimize the altitude loss. Planning will prevent this from developing into a situation in which ground contact becomes either imminent or inevitable. if you are unable to maintain altitude, begin to consider escape routes. We know (hopefully) to approach ridge lines with sufficient altitude to compensate for air descending faster than you can climb. Also approaching a ridge at a 45 degree angle will allow you to bail out away from rising terrain with a 90 degree turn rather than a 180.

If all else fails, trading off kinetic energy for a decreased sink rate will minimize the impact forces. If you plan properly, this will not have to come into play.

With a windshear- specifically downburst or microburst- the conventional wisdom is to use all of the aircraft's energy to avoid hitting the ground until you have transited the shear. As mentioned above, the pitch up into the relative wind also helps with regard to angle of attack. This means reacting at the first indication of the shear and pulling it up to the shaker and hoping for the best.

This phenomenon is very localized and the strategy is to keep the plane airborne for the 1/2 mile or so it will take to fly out the other side.

The current windshear escape maneuver came from the investigation of the famous Delta 191 accident. They tried to hold Vapp and glideslope the whole time as they flew from a headwind to a downdraft to a tailwind (microburst). It wasn't until the last couple of seconds that the captain called for TOGA and by that time it was too late.

As they descended through 1000 AGL the airspeed began to rise and they went high on the glideslope (increasing headwind shear). The NTSB determined that had they firewalled thrust and pitched to the shaker as soon as that occurred, they would have missed the ground by 300 feet.

 

[JediNein]

I guess there are those that consider 300' as not close to the ground. Maybe I should clarify, too... That wasn't in a helicopter. But, generally, I was talking about cruise, not past the point of no return (Vref @ short final). There, remember the engine teardown is cheaper than the post-accident teardown.

Using Va or maneuvering speed assumes that you are prepared for the windshear and then you want as much energy on the aircraft if possible so you can zoom climb if required - trading excess knots for altitude, or absorb a sudden loss of airspeed.

This is not the assumption I'm using. Va means pointing the nose down and accelerating out of the downdraft area. Va minimizes total time in the downdraft. Vy gives a longer exposure and a lower altitude when clear than Va.

The escape route should have already been chosen, 8000 fpm down is not the time to be formulating plans.

From Sparky Imeson's "Mountain Flying Bible":
X
.
ESCAPING DOWNDRAFTS

1. Transition to VX.

2. Turn toward lower terrain.

3. If the rate-of-descent exceeds the expected rate-of-climb at that density altitude, transition to cruise airspeed (or maneuver speed, if turbulent) to escape the downdraft faster with less overall altitude loss.

Also pop over to http://www.mountainflying.com/pdf%20files/CAP.pdf
and look at page 50. The table shows the total altitude loss, distance away from the mountain, and a 1400 fpm downdraft. Yeah, Vy is less altitude loss in 30 seconds, but you're still in the downdraft.

I thought Delta taught an unsuccessful maneuver as SOP after that microburst accident. And it wasn't the NTSB that figured out the maneuver, it was an upgrading FO. Any Delta guys care to comment?

Fly SAFE!
Jedi Nein

 

[A Squared]

I guess there are those that consider 300' as not close to the ground.

Yeah, well I get nosebleeds easily. <g> Seriously though, when I said close to the ground, I meant starting the encounter close to the ground. In the 2 encounters you mention, one began at 5000' AGL, the other being IFR in mountainous terrain, presumably began at least 2000' AGL (unless it was on approach or departure)

I agree, if you have altitude to lose and the downdraft exceeds your climb rate, going as fast as you can will get you out of the downdraft soonest. However, if you don't get out soon enough and your wheels are starting to slap tree branches, are you still going to keep the nose down and maintain Va right up to the impact?? Me, I think I'd try pulling up at that point.

Your link may have some interesting information, I'll never know though. I so far have been unable to get past the first page where the CAP Bestows on itself the title:

Mountain Fury*

without collapsing in hysterical laughter BWWWAHAAHAHAHHAHAHAHAHAH!!!!

And the CAP wonders why people laugh at them. !!????!!!




* text coloration accurately reproduced

 

[ThomasR]

DownDraft

Army instruction is to enter a ridge line at a 45 degree angel and anticipate down draft turbulence on the leeward side, different intensities at varying altitudes. Nothing can prepare you in a small aircraft getting under a 747 with flaps on an approach.

 

[Jeff Helgeson]

Best description of proceedure.

Don't know the procedure for a prop a/c but I would think it's the same.

We're trained to pull the nose up to the stick shaker and maintain that pitch until recovery or impact. Two thoughts here. One, you're making a maximum effort to fly out of the downburst. Two, if its unrecoverable, you're at nearly the slowest speed possible prior to impact. Also something to think about is aircraft configuration. We've been taught to NOT change the configuration until recovery. For example, changing flap position will cause a momentary sink that could cancel any positive climb you've attained. Same for the gear. Again, two thoughts on this. One, raising the gear, what happens? In most aircraft you get gear-well doors that open which increases drag. Granted, it's minimal but you need absolutely everything you've got so why make it worse? Second, should an impact be unavoidable, you're gear is already down.

Newer avionics platforms also give you some indication of max pitch on the PFD as a reference.

2000Flyer

Pitch is more important than airspeed, do not change configuration until in the recover phase.

DC9/MD80: in the sim I found that flying just inside the edge of stick shaker and don't go below 115 to 120 knots works best. If you hang at 110 KIAS, you will hit the terrain tail first. Also, keep the radar altimeter in your scan. If you get below 100', release a little back pressure and let it fly out.

Jeff

 

[JediNein]

And the CAP wonders why people laugh at them. !!????!!!

While my opinion about the organization with the initials CAP is not favorable at this time, Sparky Imeson's knowledge is not due to that association, same with the other co-authors.

I don't see you writing a book on mountain flying A Squared. It's a really good way to get some recognition, income, and be able to give a little back to the world.

Fly SAFE!
Jedi Nein

 

[ThomasR]

T-Cell Downdraft

I have a question, it might be stupid though; since I don't, or ever did, fly the really big stuff my perspective toward storm related downdrafts is one of avoidance. However, for reference sake, penetrating a T-Storm of a big cumulonimbus type the core pillar of the system is of a downdraft construction at higher altitudes. While winds at the lower altitudes is flushed outward creating updrafts.

What might the thickness of this outer layer be before you hit the the core downdrafts [approximate]?

If the downdraft is reaching 100 knots (???) [rule of thumb]. What minimum ASL would you have to enter the system and maintain enough AGL to exit in one piece?

 

[CUEBOAT]

what is common to use for first indication of a downdraft? severe increase in sink rate? Also when recovering from a downdraft are you guys talking about aborting the landing or just trying to stay in the air enough to make it to the runway? What is the procedure?

 

[Uncle Sparky]

I have a question, it might be stupid though; since I don't, or ever did, fly the really big stuff my perspective toward storm related downdrafts is one of avoidance. However, for reference sake, penetrating a T-Storm of a big cumulonimbus type the core pillar of the system is of a downdraft construction at higher altitudes. While winds at the lower altitudes is flushed outward creating updrafts.

What might the thickness of this outer layer be before you hit the the core downdrafts [approximate]?

If the downdraft is reaching 100 knots (???) [rule of thumb]. What minimum ASL would you have to enter the system and maintain enough AGL to exit in one piece?

One individual, textbook cell, as you describe, can be ten's of miles across. I guess, as much as several miles, might answer your question.

Several Miles, would apply to the width of the outer layer AND the altitude you might want to consider.

All kidding aside.......Some of the worst beatings I have gotten were from "little" 250 size thunderstorms. Thunderstorms are dynamic. You never know what you're going to get. There's really no fixed set of rules regarding dimensions or what your going to experience.
If you're really bored, like I am right now, you could try this: Take your typical Summertime FL600 whopper and convert that to NM. Easy enough...10NM
Let's say the cell is one-third as wide as it is tall. ......3.33NM
If you're in your typical light a/c travelling at 120kts, that'll take 1:40 to cross the base of this thing. So if you get slammed with a 5,000fpm downdraft you'll need at least 8,400 feet to level off at 100'AGL.

I'd probably stick with the avoidance idea that you mentioned earlier.