Interesting PIREPs

[MusicMan]

When I read these PIREPs I can't help to think what it must have been in the airplane. Based on the number of flights a day Severe Turbulence is not that common but it happens daily. I have never experienced Severe, thank God, even when I fly quite often. Only some good cases of Moderate where the airplane is fishtailing, dropping, rocking side to side, the whole nine yards.

PIREP 19:20Z 02/18/08

EWR UUA /OV EWR /TM 1920 /FL060 /TP B737 /TB MOD-OCNL SEV /RM UDDF COULDNT HOLD ALTITUDE

--> This is a 737 not being able to "hold altitude". So as a pilot what do you do in those cases?


PIREP 19:25Z 02/18/08

CHS UUA /OV CHS112117/TM 1925/FL330/TP B733/TB SEV/RM ZJX

--> I guess that means the airplane was out of control for at least a moment?


PIREP 18:17Z 03/06/08

ARA UUA /OV LFT180018 /TM 1817 /FL060 /TP C172 /SK SKC /TB SEV CAT /RM NEARLY FLIPPED OVER

--> This is a small airplane, but almost flipping over?


MM

[FlyingPhotog]

I wasn't aware that 737s can't hold altitude? Are you sure?

[flyboy2548m]

PIREP 19:20Z 02/18/08

EWR UUA /OV EWR /TM 1920 /FL060 /TP B737 /TB MOD-OCNL SEV /RM UDDF COULDNT HOLD ALTITUDE

--> This is a 737 not being able to "hold altitude". So as a pilot what do you do in those cases?


Slow her down to turbulence penetration speed or lower and do the best you can as far as altitude.




PIREP 19:25Z 02/18/08

CHS UUA /OV CHS112117/TM 1925/FL330/TP B733/TB SEV/RM ZJX

--> I guess that means the airplane was out of control for at least a moment?


Not necessarily, at least the PIREP doesn't say that.


PIREP 18:17Z 03/06/08

ARA UUA /OV LFT180018 /TM 1817 /FL060 /TP C172 /SK SKC /TB SEV CAT /RM NEARLY FLIPPED OVER

--> This is a small airplane, but almost flipping over?


MM






I had wake turbulence actually flip me over, not almost, so yes, I can see severe chop do that.

[flyboy2548m]

I wasn't aware that 737s can't hold altitude? Are you sure?

He means the turbulence was so severe the altitude was jumping.

[brianw999]

I remember turbulence between Singapore and Cairns once that had us dropping so fast that my coffee cup was floating in mid air in front of me for 2 or 3 seconds. When it all settled down there were a goodly few green faces around and a bit of a queue for the toilets with people carrying their cabin baggage...if you get my drift ? !!

[MusicMan]

He means the turbulence was so severe the altitude was jumping.

Flyboy, when was the last time you hit severe chop? what happened in terms of altitude and attitude?

[flyboy2548m]

Flyboy, when was the last time you hit severe chop? what happened in terms of altitude and attitude?

I don't think I've ever hit severe chop. Plenty of moderate, but not severe.

[screaming_emu]

Not necessarily, at least the PIREP doesn't say that.

AIM 7-1-24

Severe Turbulence-"Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence.

[flyboy2548m]

AIM 7-1-24

Severe Turbulence-"Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence.

Concur. Notice that the AIM doesn't define "large change". 50'? 100'? 15kias? 30kias? I've certainly never had the airplane out of control, so I don't think anything I've seen would qualify as severe, except for that one wake encounter which flipped me over, but that was in a Warrior.

[screaming_emu]

Concur. Notice that the AIM doesn't define "large change". 50'? 100'? 15kias? 30kias? I've certainly never had the airplane out of control, so I don't think anything I've seen would qualify as severe, except for that one wake encounter which flipped me over, but that was in a Warrior.

Yeah, I think I've on hit severe once. It was during my instrument training and I was trying to shoot an NDB approach under the hood. That was fun seeing as I couldn't even set my DG to the compass beforehand. Head hit the ceiling a couple times.

As for the speed variations. I guess "large change" is relative to the kind of aircraft you're in and how high you are above stall speed.

[3WE]

AIM 7-1-24

Severe Turbulence-"Turbulence that causes large, abrupt changes in altitude and/or attitude. It usually causes large variations in indicated airspeed. Aircraft may be momentarily out of control. Report as Severe Turbulence.How do you define "out of control?

I think I know what the intent of "out of control is", but if you want to be technical if you want to hold altitude, heading, attitude, or airspeed, but you can't, you are technically "out of control." and that can happen in moderate turbulence.

I'm not sure you could put the intent into words, but perhaps something like you are unable to overcome or overpower turbulence-induced attitude changes....for example the plane noses over and rolls left...you pull back and crank right, but the plane continues to nose over and roll left...

[screaming_emu]

How do you define "out of control?

I think I know what the intent of "out of control is", but if you want to be technical if you want to hold altitude, heading, attitude, or airspeed, but you can't, you are technically "out of control." and that can happen in moderate turbulence.

I'm not sure you could put the intent into words, but perhaps something like you are unable to overcome or overpower turbulence-induced attitude changes....for example the plane noses over and rolls left...you pull back and crank right, but the plane continues to nose over and roll left...

To me out of control is when you're unable to control the aircraft's attitude/altitude even if you're at full deflection. That being said I'd be very hesitant to go even close to full deflection unless it was a matter of keeping the airplane upright and I was well below maneuvering speed.

[MCM]

Severe turbulence is really one of those things that you know when you've hit it.

Moderate turbulence is rough enough, and the old eyeball shake makes life difficult to fly an aircraft.

Severe turbulence is when you're just hanging on for the ride. (In a simplified sense).

There is a lot of Moderate turbulence that does get over-reported as severe, but better to over-report I suppose!

As to what you do? Try and fly turbulence penetration speed (within reason), and accomplish any severe turbulence penetration procedure your aircraft might have. Trim for the turb penetration speed and try to maintain attitude. Accept large altitude variations, as they're going to happen (unless you're going to hit the ground of course!), and allow some speed variation (but not for significant periods below the penetration speed. Oh, and hold on!

[flyboy2548m]

allow some speed variation (but not for significant periods below the penetration speed.

Out of curiosity, why can't I be below turb penetration speed? I know about above, but why not below. For example, on my aircraft turb speed is 280kias/M.75 whichever is lower. Why can't I be at say 255kias?

[screaming_emu]

Out of curiosity, why can't I be below turb penetration speed? I know about above, but why not below. For example, on my aircraft turb speed is 280kias/M.75 whichever is lower. Why can't I be at say 255kias?

I believe I remember reading that it has something to do with how long it takes to get through each of the turbulent "eddies". Not only are you trying to reduce the actual force on the aircraft, but also the amount of time that it acts on the aircraft itself. I may be way off, but I'm pretty sure I remember reading that/hearing that somewhere along the way.

[flyboy2548m]

I believe I remember reading that it has something to do with how long it takes to get through each of the turbulent "eddies". Not only are you trying to reduce the actual force on the aircraft, but also the amount of time that it acts on the aircraft itself. I may be way off, but I'm pretty sure I remember reading that/hearing that somewhere along the way.

Hmmm...

[MCM]

Turb penetration speed basically puts you right in the middle between max speed and stall/buffet speed, and is a compromise position to ensure a high margin to buffet while not also putting you too close to an overspeed.

If you remain below penetration speed, it lowers your buffet margin, and so reduces your manoeuvre margin. If you then get a large upset and angle of bank, you want to have that margin to stall.

[screaming_emu]

Hmmm...

Yeah, MCM's explanation sounds more plausible.

[flyboy2548m]

Yeah, MCM's explanation sounds more plausible.

It's certainly better worded, I'll give it that.

[MCM]

It is my (slight) rewording of the concept as explained in a Boeing produced Flight Crew Training Manual, so take up any disputes with the concept (but not the wording) with Boeing :p

But the short summary... you don't want to remain below Turbulence Penetration Speed for extended periods as your manoeuvre margin (ie margin to stall) is reduced below what the aircraft manufacturer has considered the best compromise.

I note that the manual doesn't specifically mention remaining above the speed, only below it. I guess it goes with the theory most people would prefer a small temporary overspeed rather than a stall.

[3WE]

I note that the manual doesn't specifically mention remaining above the speed, only below it. I guess it goes with the theory most people would prefer a small temporary overspeed rather than a stall.I like the theory of a slightly greater stall risk at the expense of lessening the over-speed risk.

Stalls can often be fixed whereas overspeed might lead to departed control surfaces and airfoils.

EDIT FOR CLARITY: I am not meaning "simple" overspeed, but exceeding maneuvering speed, where extreme tubulence/wind gusts might damage the plane.

The movie "Hot Shots" proves that inflight repair of over-stressed aluminum panels is difficult at best. :-)

I suppose that one could argue that you should target to remain "reasonably" below (as opposed to "right-on") maneuvering speed to address possibly dangerous speed increases, but not "excessively" below where you will "significantly" comprimise control effectiveness.

Enough weasel words?

[MCM]

We're discussing the situation of not being sustained below a turbulence penetration speed (not manoeuvring speed) of evidently a significantly sized aircraft (its 280kts/.78), or of the 2 737's mentioned in the report. And it is for that reason that once again I have to completely disagree with you.

What you say has some credence for a light aircraft, where remaining around Va is the best you can do for turbulence penetration.

That isn't the case in larger aircraft where the turbulence penetration speed (or range of speeds) is very different.

Personally (and of course feel free to ask around for other opinions), I think that a minor overspeed of the aircraft is nothing compared to the horrible situation of a stall or spin in a big aircraft. And thats why the Boeing manual is worded (I believe) like it is.

I suppose you could always just ask Mr Boeing and see what they say!

Edited to add: AJ you've been very quiet... what does your training department suggest? ;)

[3WE]

.....a minor overspeed of the aircraft is nothing compared to the horrible situation of a stall or spin in a big aircraft....

"Acknowledged" on your other comments.

This comment intrigues me. Is a brief, turbulence-induced stall really that horrible?

I can remember a thread long ago where folks went near-ballistic when someone suggested that stalls were "bad".

In this other thread I had to write a paragraph to explain that it is fairly bad to stall airliners: 1) Flameouts tend to happen due to intake-flow disruptions, 2) the plane isn't really designed to be routinely stalled, 3) Some planes (T-tailed in particular) tend to enter "deep stalls" where the h-stab may be ineffective for recovery and 4) it would be a horrendous dereliction of airmanship to inadvertently stall an airliner in normal winds & operations. I'm sure there's some more reasons too!

I'm going to stick my neck out (sorry Flyboy) but I would guess that a stall in extreme turbulence would "generally" be recoverable. This is because (I would guess) that a decent relative airflow would be quick-to-return to the wings as you promptly exited the "killer" negative shear and/or "killer" sudden-AOA-exceeding updraft.

I would guess that there are not "killer," "gigantic," mile or more wide windshears where you loose speed and/or exceed the critical AOA....(see pedantic footnotes 1 & 2). If you stalled, I would envision it to be brief with a chance for recovery to happen very quickly before engines flamed out or a deep-stall occurred.

i.e. is there really turbulence out there that is big, and "homogenous"/long-lived enough to keep an airliner stalled long enough to have flameouts, deep stalls, or spins.

And all of this discussion aside, are there any known cases of a plane stalling when they were trying to fly near turbulence penetration or maneuvering speed. (This gets pedantic footnote #3)

I wonder if all this "stall talk" is of any practical significance? Certainly, there have been in-flight breakups, but they may be more associated with a loss of control, than a simple "killer" wind gust. But any cases of stalls directly occuring from serious turbulence/negative wind shear/sudden violent updrafts exceeding AOA???

Thanx.

*Pedantic footnotes:

1. Ok, updrafts and windshears & updrafts can be miles wide, but I am asking if you can really get mile-wide plane-stalling ones where the pilot cannot quickly recover from the stall.

2. We must never forget: loosing speed doesn't make a wing stall in and of itself- it's exceeding the critical AOA that makes the stall!

3. For further clarification- it is probably hard to stall when you are AT tubulence penetration speed- this situation is that the pilots were trying to maintain the speed, but encounter severe negative wind shear and/or updrafts and then entered an extended stall.

[MusicMan]

Stalls can often be fixed whereas overspeed might lead to departed control surfaces and airfoils.


Translation for the lay people out there:

You go too fast during turbulence and parts of the airplane may start flying off due to the stress. If you go too slow you may start dropping but it would be easier to regain control.


MCM: you a pilot?

MM

[flyboy2548m]

"Acknowledged" on your other comments.

This comment intrigues me. Is a brief, turbulence-induced stall really that horrible?

I can remember a thread long ago where folks went near-ballistic when someone suggested that stalls were "bad".

In this other thread I had to write a paragraph to explain that it is fairly bad to stall airliners: 1) Flameouts tend to happen due to intake-flow disruptions, 2) the plane isn't really designed to be routinely stalled, 3) Some planes (T-tailed in particular) tend to enter "deep stalls" where the h-stab may be ineffective for recovery and 4) it would be a horrendous dereliction of airmanship to inadvertently stall an airliner in normal winds & operations. I'm sure there's some more reasons too!

I'm going to stick my neck out (sorry Flyboy) but I would guess that a stall in extreme turbulence would "generally" be recoverable. This is because (I would guess) that a decent relative airflow would be quick-to-return to the wings as you promptly exited the "killer" negative shear and/or "killer" sudden-AOA-exceeding updraft.

I would guess that there are not "killer," "gigantic," mile or more wide windshears where you loose speed and/or exceed the critical AOA....(see pedantic footnotes 1 & 2). If you stalled, I would envision it to be brief with a chance for recovery to happen very quickly before engines flamed out or a deep-stall occurred.

i.e. is there really turbulence out there that is big, and "homogenous"/long-lived enough to keep an airliner stalled long enough to have flameouts, deep stalls, or spins.

And all of this discussion aside, are there any known cases of a plane stalling when they were trying to fly near turbulence penetration or maneuvering speed. (This gets pedantic footnote #3)

I wonder if all this "stall talk" is of any practical significance? Certainly, there have been in-flight breakups, but they may be more associated with a loss of control, than a simple "killer" wind gust. But any cases of stalls directly occuring from serious turbulence/negative wind shear/sudden violent updrafts exceeding AOA???

Thanx.

*Pedantic footnotes:

1. Ok, updrafts and windshears & updrafts can be miles wide, but I am asking if you can really get mile-wide plane-stalling ones where the pilot cannot quickly recover from the stall.

2. We must never forget: loosing speed doesn't make a wing stall in and of itself- it's exceeding the critical AOA that makes the stall!

3. For further clarification- it is probably hard to stall when you are AT tubulence penetration speed- this situation is that the pilots were trying to maintain the speed, but encounter severe negative wind shear and/or updrafts and then entered an extended stall.

No need to apologize. This isn't the first time I've been utterly unable to decipher what it is you're actually trying to say.

[3WE]

No need to apologize. This isn't the first time I've been utterly unable to decipher what it is you're actually trying to say.Oh come on Flyboy, the fully-bolded sentence isn't that Gabreillian!are there any known cases of a plane stalling when they were trying to fly near turbulence penetration or maneuvering speed.

[Uncle Jay]

Certification requirements make the wing stall before it breaks in each Category

[Gabriel]

Unless I'm wrong...

Manouver speed is the speed where the max lift produces the design load. Increase the speed, pull up hard and you'll exceed the design load before stalling. Reduce the speed, pull up hard and you'll stall before exceeding the design load. It has nothing to do with the turbulent air penetration speed.

The turbulent air penetration speed is the speed where, if you encounter a standarized vertical gust, the vertical load would reach the design load. When you encounter an updraft gust, the AOA increases, thus increasing the lift. The increase in AOA is proportional to the speed of vertical gust considered (which is defined in the FARs) and inversely proportional to the airspeed. That is, for a given gust, the lower the increase in AOA. However, the increase in lift is proportional to the increase in AOA (as said, inversely proportional to the airpseed) and to the square of the airspeed. That makes the increase in lift, and in the load, proportional to the airspeed. It is a definition. It is not in the middle between the stall and max. And overspeed is not the risk in tubulence anyway. Braking the airplane from overload (not from overspeed) is.

The turbulent air penetration speed is always greater than the manouver speed, because below the manouver speed if you were hit by a strong gust (even stronger than what the FAR requires) you would stall before reaching the design load. On the other hand, you would exceed the design load if flying at the turbulent air penetration speed and were hit by a gust more violent than the standarized one (which would be rare because the standarized one is VERY violent).

That's why the turbulent air speed is the MAX turbulent air penetration speed.

That said, the turbulent air penetration covers all what is considered necesary to be safe, and with a margin, on the structural side. Flying slower would reduce the margin over the stall. That could be a problem or not, depending on the range between the turb speed and the stall speed.

[screaming_emu]

We're discussing the situation of not being sustained below a turbulence penetration speed (not manoeuvring speed) of evidently a significantly sized aircraft (its 280kts/.78), or of the 2 737's mentioned in the report. And it is for that reason that once again I have to completely disagree with you.

What you say has some credence for a light aircraft, where remaining around Va is the best you can do for turbulence penetration.

That isn't the case in larger aircraft where the turbulence penetration speed (or range of speeds) is very different.

Personally (and of course feel free to ask around for other opinions), I think that a minor overspeed of the aircraft is nothing compared to the horrible situation of a stall or spin in a big aircraft. And thats why the Boeing manual is worded (I believe) like it is.

I suppose you could always just ask Mr Boeing and see what they say!

Edited to add: AJ you've been very quiet... what does your training department suggest? ;)

Yeah, definitly would rather overspeed a little than stall in a swept wing aircraft. Swept wing planes don't stall like a 172. If you stall it, you're probably not going to "fix it"

[MCM]

That's why the turbulent air speed is the MAX turbulent air penetration speed.



Just a point, whilst I agree with most you have said, the aircraft I fly does not have a "MAX" turbulence penetration speed, it has a range of speeds to fly in turbulence. So what you said isn't always true, but for the most part is.

The question I was answering before related specifically to why you shouldn't maintain a speed significantly below Turb Penetration speed for extended time, and I stick to the fact that it is due to reducing the margin to stall. Whether or not that is any worse than staying above Turb Pen for a significant time, well, I'll stick to whats in my FCTM.

For 3WE though, I'm sticking to my belief that I'd rather slightly overspeed a heavy jet rather than stall it. Thats all I'll say and leave it for others to make their own opinions :)

[3WE]

For 3WE though, I'm sticking to my belief that I'd rather slightly overspeed a heavy jet rather than stall it. Thats all I'll say and leave it for others to make their own opinions :)That's fine...really it is...and I note that Screamo Emo agrees and if I'm forced to encounter severe turbulence, I feel that my odds with you guys are as good as with anyone else ;-)

BUT IS ANYONE AWARE OF A PLANE BEING STALLED BY "KILLER" TURBULENCE?

I don't propose rewriting anyone's flight manual - manufacturer's or personal flight manual! But it's a valid question if a plane has ever outright stalled from extreme windshear or turbulence.

[flyboy2548m]

Oh come on Flyboy, the fully-bolded sentence isn't that Gabreillian![/b]

Ah but it is!