Structural integrity in severe turbulence
"Severe turbulence techniques"
Technique #1: Avoid at all cost!
if you mess up Technique #1, move quickly to Technique #2 and #3.
Technique #2: Slow to appropriate turbulence penetration speed for your wt. Dropping the gear will slow you quickly. Who gives a rat's arse about the gear doors!
Technique #3: Keep the wings level and try to maintain S & L attitude with smooth movements of the controls. Don't concern yourself with altitude unless you are in danger of hitting something.
If #2 and #3 fail, move on to #4.
Technique #4: Stick your head between your legs and kiss your arse goodbye, while yelling "Faaaaaaaaaaaaaaaark" at the top of your voice.
Having tangled with a standing wave over Cunningham's Gap in Southern Qld, I can vouche for the effectiveness of #2 and #3.
I have yet to test #4.
Dr
Technique #1: Avoid at all cost!
if you mess up Technique #1, move quickly to Technique #2 and #3.
Technique #2: Slow to appropriate turbulence penetration speed for your wt. Dropping the gear will slow you quickly. Who gives a rat's arse about the gear doors!
Technique #3: Keep the wings level and try to maintain S & L attitude with smooth movements of the controls. Don't concern yourself with altitude unless you are in danger of hitting something.
If #2 and #3 fail, move on to #4.
Technique #4: Stick your head between your legs and kiss your arse goodbye, while yelling "Faaaaaaaaaaaaaaaark" at the top of your voice.
Having tangled with a standing wave over Cunningham's Gap in Southern Qld, I can vouche for the effectiveness of #2 and #3.
I have yet to test #4.
Dr
FTDKiller, summed it up pretty well,
If you suspect you may run into it, eg on descent below a cumulus cloud layer or near building/developed CBs etc slow down early to turb penetration speed if your acft has one or manoeuvring speed for your weight.
Remember Va applies in the longitudinal ie pitching plane only. It DOES NOT APPLY to partial or full deflection of the rudder or ailerons.
FAR 23 and FAR 25 certification standards explain this to designers and it came as a total shock to most pilots after the American Airlines A300 lost its fin and rudder in Nov 2001 climbing out of JFK in New York.
If I remember correctly the NTSB and Airbus engineers calculated that a sideload of 80-90,000 LBS was applied to the fin/rudder which is why it failed. It was not designed for anywhere near that. The left right left deflection of the rudder even below Va generated those staggering sideloads.
That is about 40t +, the weight of a fully loaded big rig???
My point is be aware that to use up to full rudder and/or aileron deflection will require a speed well below Va to be safe. The turbulence induced gust loads you are trying to counter will only add to the aerodynamic loads caused by control deflections.
Please forgive me if my numbers are off, it was from memory.
The FAA and NTSB has published some material on this matter after this terrible crash.
If you suspect you may run into it, eg on descent below a cumulus cloud layer or near building/developed CBs etc slow down early to turb penetration speed if your acft has one or manoeuvring speed for your weight.
Remember Va applies in the longitudinal ie pitching plane only. It DOES NOT APPLY to partial or full deflection of the rudder or ailerons.
FAR 23 and FAR 25 certification standards explain this to designers and it came as a total shock to most pilots after the American Airlines A300 lost its fin and rudder in Nov 2001 climbing out of JFK in New York.
If I remember correctly the NTSB and Airbus engineers calculated that a sideload of 80-90,000 LBS was applied to the fin/rudder which is why it failed. It was not designed for anywhere near that. The left right left deflection of the rudder even below Va generated those staggering sideloads.
That is about 40t +, the weight of a fully loaded big rig???
My point is be aware that to use up to full rudder and/or aileron deflection will require a speed well below Va to be safe. The turbulence induced gust loads you are trying to counter will only add to the aerodynamic loads caused by control deflections.
Please forgive me if my numbers are off, it was from memory.
The FAA and NTSB has published some material on this matter after this terrible crash.
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We fly an aging fleet of aircraft. See how much confidence you have left in a 20,000 hour PA31 after you've just taken it through weather from hell (Noted in the log book as 'The Night from Hell') - In the dark, trying to shoot and approach while considering you would not have been the first person to have flown it through such weather.
Remember this accident involving an in-flight break up of a Chieftain?
http://www.atsb.gov.au/publications/...200506266.aspx Could it just have been the straw that broke the camel's back?
After dealing with TS every evening during summer (no wx radar no storm scope) some good advice was given:
1. Most of the TS activity is in the middle section
2. Get down to your LSALT
3. Stay visual - fly around them. This is not always possible (embedded CB / weather on the deck).
I wonder: How rough does it need to be to consider a reduction in airspeed from the green arc (allowed in rough air) to Vb? My theory is always be a gentle as possible to the airframe. I have made an approach from 10,000 with the undercarriage down in a Navajo (Vb 156kt).
Luckily most twin Cessna (excl 337) now have the SIDS program to go through, still not sure on these 20,000 hour Chieftains.
I find it interesting though, that Aero commanders were found to have fatigue cracks only after a few thousand hours. I've flew one of these a few years back that had 24,000 hours on it.
An aircraft accident involving fatalities is always tragic to any pilot whether you knew the persons involved or not. I suppose if we (humans) were meant to fly we'd have our own set of wings.
I have a book that contains aviation related quotes:
"You should never fly through a thunderstorm in peace time"
One I’d like to add (heard around the traps):
"There will be days you wished you didn't have an instrument rating"
I think private pilots are onto something.
Remember this accident involving an in-flight break up of a Chieftain?
http://www.atsb.gov.au/publications/...200506266.aspx Could it just have been the straw that broke the camel's back?
After dealing with TS every evening during summer (no wx radar no storm scope) some good advice was given:
1. Most of the TS activity is in the middle section
2. Get down to your LSALT
3. Stay visual - fly around them. This is not always possible (embedded CB / weather on the deck).
I wonder: How rough does it need to be to consider a reduction in airspeed from the green arc (allowed in rough air) to Vb? My theory is always be a gentle as possible to the airframe. I have made an approach from 10,000 with the undercarriage down in a Navajo (Vb 156kt).
Luckily most twin Cessna (excl 337) now have the SIDS program to go through, still not sure on these 20,000 hour Chieftains.
I find it interesting though, that Aero commanders were found to have fatigue cracks only after a few thousand hours. I've flew one of these a few years back that had 24,000 hours on it.
An aircraft accident involving fatalities is always tragic to any pilot whether you knew the persons involved or not. I suppose if we (humans) were meant to fly we'd have our own set of wings.
I have a book that contains aviation related quotes:
"You should never fly through a thunderstorm in peace time"
One I’d like to add (heard around the traps):
"There will be days you wished you didn't have an instrument rating"
I think private pilots are onto something.
Last edited by Triple Captain; 4th Aug 2007 at 03:50.
One I’d like to add (heard around the traps):
"There will be days you wished you doing have an instrument rating"
I think private pilots are onto something.
"There will be days you wished you doing have an instrument rating"
I think private pilots are onto something.
Huh?
10 characters
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"You should never fly through a thunderstorm in peace time"
It may or may not originate with the USAF 555th Fighter Squadron.
Above the squadron operations desk at their home base in Arizona in 1965, a sign: "There is no reason to fly through a thunderstorm in peacetime."
Above their squadron operations desk in Udorn, Thailand, in 1966: "There is no reason to fly through a thunderstorm."
Silly Old Git
I wondered about descent in areas of mechanical/ thermal turb. like around Karratha?
If you were in cloud getting banged around that much you would probably consider slowing down a tad
Dont fly old airplanes from the West
If you were in cloud getting banged around that much you would probably consider slowing down a tad
Dont fly old airplanes from the West
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The following are extracts from the Beech 36 manual which backs up the Doctors post.
1. Flight in severe turbulence must be avoided. (To remind – severe is defined as – The airplane may be momentarily out of control and occupants are thrown violently against the belts and back into the seat. Unsecured objects are tossed about)
2. You should watch particularly your angle of bank, making turns as wide and shallow as possible. Be equally cautious in applying forward or back pressure to keep the airplane level. Maintain straight and level attitude in either up or down drafts. Use trim sparingly to avoid being grossly out of trim as the vertical air columns change velocity and direction. If necessary to avoid excessive airspeeds, lower the landing gear.
3. For years, Beech POH’s and FAA approved AFM’s have contained instructions that the landing gear should be extended in any circumstance in which the pilot encounters IFR conditions which approach the limits of his capability or ratings. Lowering the gear in IFR conditions or flight into heavy or severe turbulence, tends to stabilise the airplane, assists in maintaining proper airspeed, and will substantially reduce the possibility of reaching excessive airspeeds with catastrophic consequences, even where loss of control is experienced.
4. Know your airplane’s limitations, and your own. Never exceed either.
However you should be cognisant of item 4, as one piston I flew, in the turbulence penetration procedures contained the caution “Do not lower the landing gear during flight in turbulence”. Why so? The aircraft had a gear speed of 140k (note a Beech 36 is 154 except in emergency) and the recommended turbulence penetration speed was 125 to 185k (manoeuvring speed B36 141k). You could in fact take it out to 210k and still be inside the dynamic stall limit. The Vne (no yellow arc on this aircraft) was 325k (B36 top of the green 167k) so you can appreciate from the numbers why the procedures were different. We were fortunate to have “g” meters as well, and the rolling “g” limit was two thirds of the regular limit, and I would assume this is why Beech comments about making wide and shallow turns at 2 above.
Remember too, that severe to a light aircraft will probably get a “light chop” remark from a 747 crew.
1. Flight in severe turbulence must be avoided. (To remind – severe is defined as – The airplane may be momentarily out of control and occupants are thrown violently against the belts and back into the seat. Unsecured objects are tossed about)
2. You should watch particularly your angle of bank, making turns as wide and shallow as possible. Be equally cautious in applying forward or back pressure to keep the airplane level. Maintain straight and level attitude in either up or down drafts. Use trim sparingly to avoid being grossly out of trim as the vertical air columns change velocity and direction. If necessary to avoid excessive airspeeds, lower the landing gear.
3. For years, Beech POH’s and FAA approved AFM’s have contained instructions that the landing gear should be extended in any circumstance in which the pilot encounters IFR conditions which approach the limits of his capability or ratings. Lowering the gear in IFR conditions or flight into heavy or severe turbulence, tends to stabilise the airplane, assists in maintaining proper airspeed, and will substantially reduce the possibility of reaching excessive airspeeds with catastrophic consequences, even where loss of control is experienced.
4. Know your airplane’s limitations, and your own. Never exceed either.
However you should be cognisant of item 4, as one piston I flew, in the turbulence penetration procedures contained the caution “Do not lower the landing gear during flight in turbulence”. Why so? The aircraft had a gear speed of 140k (note a Beech 36 is 154 except in emergency) and the recommended turbulence penetration speed was 125 to 185k (manoeuvring speed B36 141k). You could in fact take it out to 210k and still be inside the dynamic stall limit. The Vne (no yellow arc on this aircraft) was 325k (B36 top of the green 167k) so you can appreciate from the numbers why the procedures were different. We were fortunate to have “g” meters as well, and the rolling “g” limit was two thirds of the regular limit, and I would assume this is why Beech comments about making wide and shallow turns at 2 above.
Remember too, that severe to a light aircraft will probably get a “light chop” remark from a 747 crew.
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Technique #3 as shown in FDTKiller post.
Relating to the discussion on severe turbulence techniques be aware that on occasions the instruments & panel will shake so much that they can be difficult to interpret.
Use smooth control inputs and fly "trends"
Relating to the discussion on severe turbulence techniques be aware that on occasions the instruments & panel will shake so much that they can be difficult to interpret.
Use smooth control inputs and fly "trends"
Remember Va applies in the longitudinal ie pitching plane only. It DOES NOT APPLY to partial or full deflection of the rudder or ailerons.
FAR 23 and FAR 25 certification standards
FAR 23 and FAR 25 certification standards
Va does indeed apply to all controls but there are some additional factors for the designers:
- many aircraft types are certified to early versions of the regs, or even the old US CAR's so just don't read the current regs, go back to the applicable issue status as many things have changed over the years
- the designer must provide for full control deflection unless limited by "pilot effort". There are specified values of pilot forces for each of the controls which can mean, for many aircraft types, that only partial control deflection is designed for at Va.
I recall working with one test pilot who would easily apply more than the standard rudder pedal load. He couldn't believe it when we put a load cell on the pedal and told him how hard he was pushing.
DJPIL
As you say in many aircraft types that means partial control deflection only at Va.
The standard V/N Diagram is for load factor in the pitching plane only and of course shows the edges of any planes envelope based on its structural design limits and Va at the intersection of the stall limit at max load factor.
The Airbus accident highlighted the complexities of the FARs Part 23 and 25 which designers know well but many pilots do not.
Here in the States after the accident and the investigation there were many good articles in the pilot magazines explaining in detail the basic point I was trying to make which was that full control deflection of the aileron and or rudder at or even below Va down to some given speed will very possibly lead to a structural failure. This came as a big shock to many pilots including extremely experienced airline veterans who were unaware of this fact.
Sorry I have not recently read those FAR paras applicable.
- the designer must provide for full control deflection unless limited by "pilot effort". There are specified values of pilot forces for each of the controls which can mean, for many aircraft types, that only partial control deflection is designed for at Va.
The standard V/N Diagram is for load factor in the pitching plane only and of course shows the edges of any planes envelope based on its structural design limits and Va at the intersection of the stall limit at max load factor.
The Airbus accident highlighted the complexities of the FARs Part 23 and 25 which designers know well but many pilots do not.
Here in the States after the accident and the investigation there were many good articles in the pilot magazines explaining in detail the basic point I was trying to make which was that full control deflection of the aileron and or rudder at or even below Va down to some given speed will very possibly lead to a structural failure. This came as a big shock to many pilots including extremely experienced airline veterans who were unaware of this fact.
Sorry I have not recently read those FAR paras applicable.
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Va does indeed apply to all controls
Maneuvering speed is usually defined—without regard to asymmetrical loads—as the maximum speed at which full or abrupt combined control movements can be made without damaging the aircraft. The FAA’s AC 61-23C, “Pilot’s Handbook of Aeronautical Knowledge,” says that “any combination of flight control usage, including full deflection of the controls, or gust loads created by turbulence should not create an excessive air load if the airplane is operated below maneuvering speed.” According to the US Navy, “Any combination of maneuver and gust cannot create damage due to excess airload when the airplane is below the maneuver speed.”
The NTSB has pointed out that this broader definition, although widespread among pilots, is incorrect. Engineers consider each axis separately in designing for the air loads accompanying an abrupt, full control input at maneuvering speed. “Full inputs in more than one axis at the same time and multiple inputs in one axis are not considered in designing for these [VA] flight conditions.”
The particular “multiple inputs” that prompted NTSB comment were the rudder reversals leading to a yaw over swing followed by a final reversal that destroyed the vertical tail of American Airlines Flight 587 on November 12, 2001.
Va (maneuvering speed) is the maximum speed at which a full, abrupt elevator movement, a gust, or a combination of the two will cause the wing to stall rather than bend. (The concept of maneuvering speed properly refers to symmetrical flight conditions, meaning no aileron or rudder involved. Somehow, the definition incorrectly got extended to include those surfaces.) Va is a fixed theoretical calculation relative to Vs1. For a utility category light aircraft (whose certificated vertical load limit factor is +4.4g) Va =square root4.4*Vs1, or just over twice Vs1.
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The same as the previous.
Velocity squared divided by Vs1 = G's
For a Shrike, Vs1 approx. 67 kts, therefore 172 squared divided by 67 squared = 6.6 Gs ultimate load factor and 141 kts = 4.4 Gs design load max.
I've always been under the text book impression of all controls full deflection, but gut instinct would have you believe the combined torsional twisting moment of full aileron at a max design load won't help the cause.
Used to be that FAR 23 gust loads were based on a vertical component of 15 m/s believe it latter changed to 30m/s. But could be wrong on this.
M
Velocity squared divided by Vs1 = G's
For a Shrike, Vs1 approx. 67 kts, therefore 172 squared divided by 67 squared = 6.6 Gs ultimate load factor and 141 kts = 4.4 Gs design load max.
I've always been under the text book impression of all controls full deflection, but gut instinct would have you believe the combined torsional twisting moment of full aileron at a max design load won't help the cause.
Used to be that FAR 23 gust loads were based on a vertical component of 15 m/s believe it latter changed to 30m/s. But could be wrong on this.
M
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Va does indeed apply to all controls
As they say in "Little Britian", "Yes, but....." and the kicker is in the "but" - no pun intended. Va is certainly used as a benchmark for the design of all controls (aileron, rudder and elevator) but the prevailing pilot view that you can sit there pushing and pulling from one stop to the other while at Va is where you can come to grief big time. For those inclined look up FAR 23 at www.faa.gov - there is a lot of information on the requirements to get your head around, but a very good and simple pilot speak paper discussing this issue can be found at
http://www.flightlab.net/pdf/8_Maneuvering.pdf
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youngmic
may be may be not, whatever the case may be, if the aircraft was certified at the "old or previous" vertical component any later change is simply academic.
Think grandfathering and why it is unlikely that the type would not now be certified as is were it to be presented as a newbie, same as the B747 100.
It has always been a mystery to me (not really) why I hear so many youngsters speak in awe of a type that has such a long history. There is an inevitability and confluence of history, events and personalities here that I dare not yet discuss. When the times right perhaps.
Go to the reference to which Brian refers and have a close look at the number of amendments for each section. There is a hard earned reason for every one of them the beneifts of which aircraft certified before each amendment did not necessarily share.
Used to be that FAR 23 gust loads were based on a vertical component of 15 m/s believe it latter changed to 30m/s. But could be wrong on this.
Think grandfathering and why it is unlikely that the type would not now be certified as is were it to be presented as a newbie, same as the B747 100.
It has always been a mystery to me (not really) why I hear so many youngsters speak in awe of a type that has such a long history. There is an inevitability and confluence of history, events and personalities here that I dare not yet discuss. When the times right perhaps.
Go to the reference to which Brian refers and have a close look at the number of amendments for each section. There is a hard earned reason for every one of them the beneifts of which aircraft certified before each amendment did not necessarily share.
Thanks Brian, Well put . That looks like a great link. I will have a read when time permits. 
Good way to define it 
and as you said here
The old definition we were probably all taught at some point is just plain wrong. 
Va (maneuvering speed) is the maximum speed at which a full, abrupt elevator movement, a gust, or a combination of the two will cause the wing to stall rather than bend. (The concept of maneuvering speed properly refers to symmetrical flight conditions, meaning no aileron or rudder involved. Somehow, the definition incorrectly got extended to include those surfaces.)
and as you said here
Maneuvering speed is usually defined—without regard to asymmetrical loads—as the maximum speed at which full or abrupt combined control movements can be made without damaging the aircraft. The FAA’s AC 61-23C, “Pilot’s Handbook of Aeronautical Knowledge,” says that “any combination of flight control usage, including full deflection of the controls, or gust loads created by turbulence should not create an excessive air load if the airplane is operated below maneuvering speed.” According to the US Navy, “Any combination of maneuver and gust cannot create damage due to excess airload when the airplane is below the maneuver speed.”
The NTSB has pointed out that this broader definition, although widespread among pilots, is incorrect. Engineers consider each axis separately in designing for the air loads accompanying an abrupt, full control input at maneuvering speed. “Full inputs in more than one axis at the same time and multiple inputs in one axis are not considered in designing for these [VA] flight conditions.”
The particular “multiple inputs” that prompted NTSB comment were the rudder reversals leading to a yaw over swing followed by a final reversal that destroyed the vertical tail of American Airlines Flight 587 on November 12, 2001.
The NTSB has pointed out that this broader definition, although widespread among pilots, is incorrect. Engineers consider each axis separately in designing for the air loads accompanying an abrupt, full control input at maneuvering speed. “Full inputs in more than one axis at the same time and multiple inputs in one axis are not considered in designing for these [VA] flight conditions.”
The particular “multiple inputs” that prompted NTSB comment were the rudder reversals leading to a yaw over swing followed by a final reversal that destroyed the vertical tail of American Airlines Flight 587 on November 12, 2001.
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If I was a newbie, I could be quite confused by now.
Here's the correct answer as I understand it. Usual caveat about please correct me if I'm wrong, etc.
Va does apply to all the primary controls. It always has. The "BUT" is that it only applies to one control surface at a time, and then only for one single full deflection from neutral, as opposed to multiple L-R-L-R inputs.
Wasn't that the lesson from the oft-quoted Airbus rudder accident? Pretty much everyone knew about the first two phrases in bold, but the third was the surprising one. Guess no-one had sat there hammering away at the footrests in turbulence before.
Thanks ForkTailed one - your post very helpful.
Here's the correct answer as I understand it. Usual caveat about please correct me if I'm wrong, etc.
Va does apply to all the primary controls. It always has. The "BUT" is that it only applies to one control surface at a time, and then only for one single full deflection from neutral, as opposed to multiple L-R-L-R inputs.
Wasn't that the lesson from the oft-quoted Airbus rudder accident? Pretty much everyone knew about the first two phrases in bold, but the third was the surprising one. Guess no-one had sat there hammering away at the footrests in turbulence before.
Thanks ForkTailed one - your post very helpful.
Relating to the discussion on severe turbulence techniques be aware that on occasions the instruments & panel will shake so much that they can be difficult to interpret
One of the factors in successful handling of severe turbulence - especially at night or in IMC - is confidence and currency at unusual attitude recovery. While PPL and CPL pilots are supposedly instructed on UA recovery in a C150 and even during instrument rating renewals an ATO may require you to demonstrate competence in these manoeuvres, the fact is there is an obvious flight safety limit to demonstrating competence in a real aircraft.
Rather than disregard the problem altogether and rely on past experience at UA's in a light single engine trainer to get you out of future trouble IMC, it is worthwhile practicing UA recovery training in a synthetic trainer or full flight simulator. This way, extreme nose high/low/rolling and inverted attitude recovery can be safely recognised on instruments and no one gets hurt. Better that than nothing at all and simply relying on luck. The control forces experienced in severe turbulence cannot be replicated in simulators but the extreme attitudes displayed on flight instruments certainly can. Again - better than nothing.