Severe turbulence and RVSM
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Severe turbulence and RVSM
A month ago, a XLA B738 at FL370, suddenly appeared at FL345 (on RDD). It was only after a controller had intervened with request to verify level, that they said they're climbing again to FL370 and that they were unable to maintain level due severe turbulence (RVSM status not mentioned) It was all with the attitude like it was totally normal situation (descending and climbing without clearance), but that's different story.
Almost identical situation happened yesterday. ELG F100 lost also 2500 feet (FL330 to FL305) and informed the controller that they are climbing again to FL330. Again reason was severe turbulence, and again UNABLE RVSM DUE TURBULENCE was not reported.
So, may someone explain to me when aircraft is no longer capable of maintaining RVSM status in severe turbulence?
Almost identical situation happened yesterday. ELG F100 lost also 2500 feet (FL330 to FL305) and informed the controller that they are climbing again to FL330. Again reason was severe turbulence, and again UNABLE RVSM DUE TURBULENCE was not reported.
So, may someone explain to me when aircraft is no longer capable of maintaining RVSM status in severe turbulence?
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"..So, may someone explain to me when aircraft is no longer capable of maintaining RVSM status in severe turbulence?"
Rule is - RVSM is cancelled during Severe Turbulence - period!
About pilots not reporting it till "climbing back to assigned FL" - I totally understand...the old AVIATE - NAVIGATE - COMMUNICATE rings true.
JV
Rule is - RVSM is cancelled during Severe Turbulence - period!
About pilots not reporting it till "climbing back to assigned FL" - I totally understand...the old AVIATE - NAVIGATE - COMMUNICATE rings true.
JV
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Ok. To redefine my question. What has to happen, so that UNABLE RVSM DUE TURBULENCE is announced? ICAO Doc 4444 says it has to be reported when: ...affects the capability of an aircraft to maintain height-keeping requirements for RVSM. (12.3.1.12 REDUCED VERTICAL SEPARATION MINIMUM (RVSM) OPERATIONS). Height-keeping requirement is ±200ft from the FL, so if you lose 2500ft in few seconds you do not meet the requirement. Or you do?
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Jovica
While I am not in a position to comment specifically on this case, if they indeed lost 2500ft in 'a few seconds', that would equate to a rate of descent well over 10000fpm. As a pilot I would be much more concerned initially with that than with telling ATC what was happening. Once controlled flight had been resumed, ATC would be right up there at the top of my list.
Height-keeping requirement is ±200ft from the FL, so if you lose 2500ft in few seconds you do not meet the requirement. Or you do?
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Gents, the moderator has given the link to this thread in a current thread running on the main board ( http://www.pprune.org/forums/showthread.php?t=286071 ). It's a long thread, but to give you all a précis of what I’m suggesting: the accuracy of modern GPS is such that if some individual does make a mistake, (or do something totally *** stupid by not speaking up very loudly and immediately after being unable to maintain altitude, as might well be the case in the instance quoted by jovica), and there's conflicting traffic, they will be on exactly the same lateral path, and unless immediate – and just as importantly, correct - avoiding action is taken by both pilots, (remember the Russian/DHL tragedy over southern Germany), they WILL hit each other, as was the case recently in Brazil.
I’m suggesting that whenever the aircraft is above 20,000' and in the normal navigation mode, (on a Boeing, "LNAV" mode), a lateral offset of .5NM be inbuilt in the FMS. If it is considered by the mathematicians who design airways (as I believe it is) that a .5NM offset would cause too many problems with crossing traffic separation, an offset of as little as .1NM, (which I can’t see causing any problems at all), would be enough. THAT’S HOW ACCURATE THE NAV SYSTEMS ARE.
Whenever the aircraft is below 20,000', or if above that level, is given vectors by a controller (and therefore, the FMS is in "HDG SEL" mode), the offset would not be active. (I’d see the software built in such a way that the offset would not become active until ‘n’ minutes (say 4?) after LNAV was selected and then it would gradually take up the offset.)
Many ATCOs seem to see any suggestion along these lines as a personal affront to their professionalism. It’s anything but that, just an admission that even in the very best of systems, an unknown and totally impossible to plan for factor can intrude, (as in the case quoted by jovica). Surely, if that’s accepted, (and I’m damned if I can see how it can’t be accepted), putting another very easily implemented procedure in place that in the case of opposite direction traffic on the same airway, will offset both aircraft slightly from exactly the same lateral line over the earth’s surface has to be an improvement in the overall safety of the ATC system – and that’s what we’ve all here for, isn’t it, both pilots and controllers?
I know this suggestion doesn’t address the problem of crossing traffic, but you don’t need to be a rocket scientist to understand that if two aircraft hit while crossing the same piece of airspace, which they both occupied for only an instant, both have to be in that one spot at exactly the same time as well as one of them being at the wrong altitude. In the opposite direction traffic situation, it just takes one mistake and they can both be on the same exact line both laterally and vertically for many, many hours on end.
I’m suggesting that whenever the aircraft is above 20,000' and in the normal navigation mode, (on a Boeing, "LNAV" mode), a lateral offset of .5NM be inbuilt in the FMS. If it is considered by the mathematicians who design airways (as I believe it is) that a .5NM offset would cause too many problems with crossing traffic separation, an offset of as little as .1NM, (which I can’t see causing any problems at all), would be enough. THAT’S HOW ACCURATE THE NAV SYSTEMS ARE.
Whenever the aircraft is below 20,000', or if above that level, is given vectors by a controller (and therefore, the FMS is in "HDG SEL" mode), the offset would not be active. (I’d see the software built in such a way that the offset would not become active until ‘n’ minutes (say 4?) after LNAV was selected and then it would gradually take up the offset.)
Many ATCOs seem to see any suggestion along these lines as a personal affront to their professionalism. It’s anything but that, just an admission that even in the very best of systems, an unknown and totally impossible to plan for factor can intrude, (as in the case quoted by jovica). Surely, if that’s accepted, (and I’m damned if I can see how it can’t be accepted), putting another very easily implemented procedure in place that in the case of opposite direction traffic on the same airway, will offset both aircraft slightly from exactly the same lateral line over the earth’s surface has to be an improvement in the overall safety of the ATC system – and that’s what we’ve all here for, isn’t it, both pilots and controllers?
I know this suggestion doesn’t address the problem of crossing traffic, but you don’t need to be a rocket scientist to understand that if two aircraft hit while crossing the same piece of airspace, which they both occupied for only an instant, both have to be in that one spot at exactly the same time as well as one of them being at the wrong altitude. In the opposite direction traffic situation, it just takes one mistake and they can both be on the same exact line both laterally and vertically for many, many hours on end.
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Originally Posted by 410
Many ATCOs seem to see any suggestion along these lines as a personal affront to their professionalism.
For those long cruise segments on airways, it makes perfect sense.
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Pre-flight review of the route forecast and SIGWX for turbulence is a requirement for RVSM ops. Likewise reporting "unable" is a requirement if you cannot fly ±200FT in RVSM airspace.
If it was a severe turbulence encounter, then they could possibly have been busy dealing with it!
"Aircraft handling difficulties" is one of the textbook definitions of severe turb. At FL370 is it not easy to hand fly within ±200FT when it is smooth! Add severe turb and the autopilot wont be doing it either, if it hasn't disconnected.
Copied from some groundschool notes:
• Very low – below 0.05g – Light oscillations
• Low – 0.05 to 0.2g – Choppy; slight, rapid, rhythmic bumps or cobblestoning
• Moderate – 0.2 to 0.5g – Strong intermittent jolts
• Severe – 0.5 to 1.5g – Aircraft handling made difficult
• Very severe – above 1.5g – Increasing handling difficulty, structural damage possible.
Manufacturers often recommend pilots abandon hard targets or accuracy during flight in severe turbulence. From one Boeing FCOM under Severe Turbulence:
"Use autopilot in turbulence. Closely monitor autopilot
operation and be prepared to disconnect autopilot only if
airplane does not maintain an acceptable attitude. If autopilot
disconnects, pilot should smoothly take control and stabilize
pitch attitude. Fly attitude as the primary pitch reference.
Sacrifice altitude to maintain attitude. Disregard flight director
pitch bar. Do not trim manually. After recovery, autopilot
should be reengaged if available."
You can forget about ±200FT, better off calling for a block clearance in severe turbulence!
If it was a severe turbulence encounter, then they could possibly have been busy dealing with it!
So, may someone explain to me when aircraft is no longer capable of maintaining RVSM status in severe turbulence?
Copied from some groundschool notes:
• Very low – below 0.05g – Light oscillations
• Low – 0.05 to 0.2g – Choppy; slight, rapid, rhythmic bumps or cobblestoning
• Moderate – 0.2 to 0.5g – Strong intermittent jolts
• Severe – 0.5 to 1.5g – Aircraft handling made difficult
• Very severe – above 1.5g – Increasing handling difficulty, structural damage possible.
Manufacturers often recommend pilots abandon hard targets or accuracy during flight in severe turbulence. From one Boeing FCOM under Severe Turbulence:
"Use autopilot in turbulence. Closely monitor autopilot
operation and be prepared to disconnect autopilot only if
airplane does not maintain an acceptable attitude. If autopilot
disconnects, pilot should smoothly take control and stabilize
pitch attitude. Fly attitude as the primary pitch reference.
Sacrifice altitude to maintain attitude. Disregard flight director
pitch bar. Do not trim manually. After recovery, autopilot
should be reengaged if available."
You can forget about ±200FT, better off calling for a block clearance in severe turbulence!
Last edited by ITCZ; 10th Aug 2007 at 06:12.
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On the face of it, when an aircraft descends 2500' due turbulance then even old 2000' level spacing won't help. Twas probably associated with a massive loss of airspeed which is caused by a large change in direction or strength in the wind - Did his ground speed change after the incident? My prediction is that it would increase...
When these sort of wind changes occur, they TEND (ie not always) to be a once off change (well the large change anyhow). Thus the RVSM status could probably be maintained. Probably a good idea (sure you did anyhow) to advise following aircraft that theirs may not....
Watched the 737 autopilot do very well in turb. Its the change in wind that causes us to get our knickers in a twist. And I have seen quite a few in the last week.
ATB, Cough
When these sort of wind changes occur, they TEND (ie not always) to be a once off change (well the large change anyhow). Thus the RVSM status could probably be maintained. Probably a good idea (sure you did anyhow) to advise following aircraft that theirs may not....
Watched the 737 autopilot do very well in turb. Its the change in wind that causes us to get our knickers in a twist. And I have seen quite a few in the last week.
ATB, Cough
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Thank you guys for the replies. All the posts were very useful and gave some informations I didn't know. Yes, the ground speed increased immensely (over 100 kts) and information of reported severe turbulence was passed to all following ACFT along that route and FL.
However, my question is left unanswered and on a second thought, it cannot be answered at all, it seems. If the turbulence is such that the aircraft handling is difficult, pilot will request level change. Either climb or descent. Eventually, there'll be a FL for the "smooth" flight and it can be within the RVSM airspace. In that case, reporting UNABLE RVSM DUE TURBULENCE is improper and useless. In the other hand, a simple request for FL280 or 270 may solve the problem as well.
Still, it raises another question. What's the point in UNABLE RVSM DUE TURBULENCE in the first place? I doubt I'll hear that one in my career...
However, my question is left unanswered and on a second thought, it cannot be answered at all, it seems. If the turbulence is such that the aircraft handling is difficult, pilot will request level change. Either climb or descent. Eventually, there'll be a FL for the "smooth" flight and it can be within the RVSM airspace. In that case, reporting UNABLE RVSM DUE TURBULENCE is improper and useless. In the other hand, a simple request for FL280 or 270 may solve the problem as well.
Still, it raises another question. What's the point in UNABLE RVSM DUE TURBULENCE in the first place? I doubt I'll hear that one in my career...
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From my distant past in reading this stuff...if there is an area of known or forecast severe turbulence, then RVSM should be cancelled til it goes away.
A good example of this would be a tropical cyclone.
A good example of this would be a tropical cyclone.
