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-   -   A query on chop (https://www.pprune.org/passengers-slf-self-loading-freight/383565-query-chop.html)

Sober Lark 2nd Aug 2009 14:43

A query on chop
Can anyone advise what measure is used to indicate severity of turbulence.

Trvelled DUB to MRS (21.44) last night 01 Aug and probably south of Lyon we went through a rough patch. Certainly not a nervous pax and fly 50 k plus a year but the roughest I experienced in say 10 years. Beaufort scale to describe wind speed but I am curious is there a similar scale of 1 to something to describe turbulence. Many thanks for any feedback.

Rainboe 2nd Aug 2009 18:56

Not quite correct.
Light- rings appear in Captains tea
Moderate- Captains tea slopping over. Cabin crew down back phoning pleading for seatbelts.
Severe- Captain cannot connect fork with mouth and keeps stabbing cheek. Unable to keep tray on lap. Food occasionally takes off. Instruments can become unreadable for long periods. Stewardess looks frightened.

Intermittent means sudden jolt that gets everybody screaming. We like those.
Continuous means Captain's food gets cold.

boardingpass 4th Aug 2009 00:13

YES, We DO like those. How often I've been tempted to make a PA to say it's more fun if you put your hands in the air.

Sober Lark 8th Aug 2009 06:18

Thanks all!

To create an even better PAX reaction I'd imagine you could play Tom Perry's 'Learning to fly' at full volume over the PA?

Romeo Delta 8th Aug 2009 21:38

How often I've been tempted to make a PA to say it's more fun if you put your hands in the air.
Reminds me of a recent flight from ATL to SLC. The Rockies are always a joy when it comes to shakers, and this was no exception. Like the ride at the carnival where you're lifted high in the air, and then dropped. No clue how far we dropped each time, but it was enough to bring your stomach up to your throat. Plenty of screaming and crying was heard. And that was just the MEN...

And all I wanted to do was throw my hands in the air like I was on a roller coaster... ;)

(Pax'ing 125k miles a year will do that to you...)

Otto Throttle 10th Aug 2009 12:30

Chop and turbulence are not the same.

The definitions above are for the 3 main categories of turbulence. There are only 2 categories of chop that I am aware of, light and moderate.

Light chop is like driving over cobblestones - a continuous 'bumping' or rumbling type of sensation. It tends to have a fairly regular and rapid rythm. Moderate chop, a more exaggerated version of light chop, with more obvious 'bumps'. Neither one leads to any noticeable change in aircraft attitude, altitude or speed. Anything more bumpy or unpleasant falls into the category of turbulence.

Sober Lark 11th Aug 2009 11:14

Thank you for pointing that out Otto.

I am surprised there are so few categories for example severe turbulence goes from Wingo's "The aircraft by be out of control for short periods accompanied by large variations in airspeed. Occupants are forced violently against seat belts. Loose objects are tossed around." to actual aircraft break up. The Boeing 777 wing load test YouTube - Boeing 777 Wing Load Test is interesting. One would imagine they would have failed much earlier with lesser forces outside such a controlled laboratory environment.

Otto Throttle 11th Aug 2009 14:36

There is also a category of extreme turbulence, although without actually trawling around for a definition, I couldn't say with certainty that it is an 'official' category.

Either way, it's a bit of a moot point in that any pilot with half a brain will avoid any area with reported or expected severe turbulence (most will also avoid moderate), or get out of just as soon as they possibly can. Nobody would wish to explore any higher categories of turbulence, and so a definition would be somewhat lacking in usefulness.

Rainboe 12th Aug 2009 11:34

There is also a category of extreme turbulence, although without actually trawling around for a definition, I couldn't say with certainty that it is an 'official' category.
This is the fabled 'Vindaloo' level. Some hairy chested experienced pilots (like 411A and me) have experienced it. There is one more level 'Phal'- you don't want that! Nobody has survived to tell the tale!

I guess I have 'half a brain', but the truth must be told.

A lot is being made of this 'pilots will avoid areas of severe turbulence'. I'm afraid not. When one looks at the weather charts, these are frequently marked. Whilst notice is taken, one will never reroute on that basis. Otherwise nobody would be able to get to SIN in thunderstorm season- often you have to just batten down the hatches and penetrate thunderstorm areas as best you can. It is remembered that these charts are produced within the bounds of modern meteorological knowledge. They are very unrelaible. One would warn the cabin crew when it was likely to be encountered (to assist with planning cabin service), but that is as far as it goes. I have never ever altered a planned flight for this reason. Once airborne, one can attempt to get other pireps (pilot reports of actual turbulence encountered) and study the weather radar, but no other means is available or reliable enough. One will usually not even bother leaving seat belt signs on if you are not certain it will be encountered (unless you are American with a plane load of potential litigants). Maybe that will change as this new era of humanity tends to sue if they go to sea in a cruise ship and get hit by a storm!

That is the true current policy. I see nothing wrong with it. There will always be the odd unexpected encounter that will leave head marks in cabin furnishings, but it has been found to be of acceptable safety in aviation today.

Sober Lark 12th Aug 2009 15:46

Is this the 'Vindaloo' level?
Is this the 'Vindaloo' level?

YouTube - Flying through Iraq thunderstorm

Rainboe 13th Aug 2009 21:45

That's it! Pretty spicey! That's as bad as I've ever known St.Elmos. I used to like getting the cabin crew up to see 'St Elmos Fire'. They'd come up and I'd direct them out of the window. Seeing nothing, they would park their face right at the window just as it flashed a burst- it comes across as an instantaneous incredibly ornate tree across the screen. They would usually retreat rapidly with a white face! It gives a very bizarre and strange atmosphere on the flight deck- the lightning bolts complete it. When it's really bad, you get continuous rippling of lightning discharges enough to read by. The worst storms for that I have ever seen have been Northern Pakistan near the Indian border.

The only music to play in it is Wagner's 'Ride of the Valkyries'. Nothing else will do, but you are usually too busy trying to stay alive!

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