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Light Vs. Moderate Vs. Heavy Chop  
User currently offlineFlashmeister From United States of America, joined Apr 2000, 2917 posts, RR: 6
Posted (13 years 2 months 1 week 11 hours ago) and read 15530 times:
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Question to the pilots on the board...

When listening to Channel 9 on my latest flights PHL-ORD-PDX, I took some interest in hearing how pilots characterized the ride to ATC.

What's the determination between calling some turbulence light, moderate, or heavy? I never heard the heavy, but we were going through some pretty serious bumps it seemed, and all the pilots said was 'constant moderate chop', although one NW pilot said 'we're getting pretty beat up here' and requested higher.

So what's the line between light, moderate, and heavy?

10 replies: All unread, jump to last
User currently offlineRalgha From United States of America, joined Nov 1999, 1614 posts, RR: 5
Reply 1, posted (13 years 2 months 1 week 10 hours ago) and read 15509 times:

Light Turbulence: slight, erratic changes in altitude/attitude. Occupants may feel slight pressures against straps, unsecured objects may be slightly displaced.

Light Chop: slight, rapid, somewhat rhythmic bumps without appreciable changes in altitude/attitude.

Moderate Turbulence: similar to light, but greater intensity. Aircraft is always in positive control, usually causes variations in indicated airspeed. Occupants feel definate strains against straps, unsecured objects are dislodged, walking is difficult (assuming the aircraft is big enough to walk in).

Moderate Chop: similar to light chop, greater intensity, still no appreciable changes in altitude/attitude.

Sever Turbulence: large, abrupt changes in altitude/attitude, large variations in airspeed, aircraft may be momentarily out of control. Occupants are forced violently against straps, unsecured objects disappear, walking is impossible.

Extreme: Violently tossed about, practically impossible to control, may cause structural damage.

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User currently offlineJhooper From United States of America, joined Dec 2001, 6206 posts, RR: 11
Reply 2, posted (13 years 2 months 6 days 15 hours ago) and read 15435 times:

Ralgha's definitions are correct. As bad as I've seen it get, I don't think I've ever characterized turbulence any greater than moderate because it implies that the aircraft is out of control.

Last year 1,944 New Yorkers saw something and said something.
User currently offlineSaab2000 From Switzerland, joined Jun 2001, 1621 posts, RR: 11
Reply 3, posted (13 years 2 months 6 days 12 hours ago) and read 15403 times:

When I took my "voice course" here in Europe I was told NOT to use the word "chop" as it is considered American slang and that is a no-no here in Europe. I think that Ralgha is right though in his definitions.

Light is anything less than moderate, which is defined as (translated from German) "walking becomes difficult". Severe would be when the airplane is essentially on the edge of control. I have seen moderate to severe but never extreme turbulence. Hopefully I never will. I have some friends here who have experienced it and said that until you experience severe-extreme turbulence you think it is funny. After you have seen severe or extreme you will have a much higher respect for it - books flying around the cockpit, anyone who is not belted (including F/As) will be flying around the cabin, glasses and plates in the trolleys are broken, etc.

User currently offlineFlashmeister From United States of America, joined Apr 2000, 2917 posts, RR: 6
Reply 4, posted (13 years 2 months 6 days 9 hours ago) and read 15379 times:
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At the point where our pilot was reporting moderate chop, it would have definitely been difficult to walk, especially if you weren't tall enough to use the bins as a gripping point. The FA's were seated, and people went running out of the lavs back to their seats.

We hit some pretty serious jolts -- couple of the bins flew open with some light stuff falling out, sounded like there was some stuff coming off counters in the galleys, etc.

Good to know though that what was being reported was just moderate -- although from the passenger's perspective, it seemed rather severe.

User currently offlineInbound From Trinidad and Tobago, joined Sep 2001, 856 posts, RR: 2
Reply 5, posted (13 years 2 months 6 days 8 hours ago) and read 15368 times:

i remember during my PPL training and when I just started to go solo, especially on cross countries...
the lightest turbulence seemed severe !!

I mean, there's the text book definition of classes of turbulence as mentioned above, but in my opinion, there's also your personal tolerance of turbulence as well.

Maintain own separation with terrain!
User currently offlineSaab2000 From Switzerland, joined Jun 2001, 1621 posts, RR: 11
Reply 6, posted (13 years 2 months 6 days 1 hour ago) and read 15341 times:

Inbound is right too! When I got my PPL I too thought that anything was severe! I was not a born flyer but I had to learn that such things were normal.

User currently offlineB747skipper From , joined Dec 1969, posts, RR:
Reply 7, posted (13 years 2 months 6 days ago) and read 15347 times:

Pilots - think about your "seat belt sign" use... for turbulence...
Light, moderate or severe, I personally do not "overdo it" with the seat belt sign ON... for this simple reason...
If we are in constant or occasionally "ligh" turbulence, a seat belt sign ON could be a good idea... leave it ON, for an hour (as you forget about it) and people need to go to the toilets, they will start to disregard that sign...
If you later decide that not light, but moderate (or worse) is going to be on your flight path... well, your passenger's observance of the seat belt sign ON has been lost... they will say "that pilot forgets about it when it is ON" or worse, "that pilot puts it on for NOTHING"...
Our flight attendants have been issued a new directive, last year, when they come by to serve drink or food, is to "remind" the passengers about using a seat belt as they are seated, does not need to be tight...
Sure - this is a part of our passenger briefing when we turn the seat belt sign off after departure, but our passenger get that reminder some two or three times during the flight with drinks and meal service... We may be a "third world little airline" but we exceed even US-FAA standards as far as safety recommendations...
Legality of all this, an injured passenger who did not wear his seat belt when seated will never win in the courts against us... and if he goes to the toilet when the seat belt sign is ON, tough luck to win in courts...
Our flight attendants are heroes, up to a limit... when they are told "cabin staff please take your seats"... they know what it means... last year we got one who suffered a broken leg, trying to help a passenger who was not seated... they now have instructions to stay strapped on their crew seat...
(s) Skipper

User currently offlineCx340 From Mexico, joined Sep 2000, 609 posts, RR: 4
Reply 8, posted (13 years 2 months 5 days 8 hours ago) and read 15298 times:

Can somebody help me understand turbulence? I know the basics, but why does it vary in intensity? How possible is it to determine where it might hit you (I know when is practically impossible)? I used to be ok with it until I was involved in a clear air turbulence incident in May 2001. I'm sure it was not extreme and probably even not severe, but the pilot sure was scared when he came on the pas system and flight attendants (on of whom was injured) were even crying. . .not nice. Now every time I fly I'm a little nervous. I don't really have a problem with turbulence when crossing clouds because I expect it , but CAT. . .

User currently offlineJhooper From United States of America, joined Dec 2001, 6206 posts, RR: 11
Reply 9, posted (13 years 2 months 5 days 7 hours ago) and read 15271 times:

The way I think about it is to imagine a lake and the waves that rock boats. It's similar to that.

Last year 1,944 New Yorkers saw something and said something.
User currently offlineFlashmeister From United States of America, joined Apr 2000, 2917 posts, RR: 6
Reply 10, posted (13 years 2 months 4 days 15 hours ago) and read 15236 times:
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It was interesting on the flight I was talking about -- the pilots kept the Seat Belt sign off most of the time when we were in just the light stuff, but when they needed to, they'd pop the sign on and just come over the PA briefly and say "Seat Belts, please". That's all.

People generally followed instructions, which surprised me. I think the reminder from the flight deck is what did it -- most of the time, it's just totally disregarded...

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