c5load
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Why Is A Heavy Called A Heavy?

Sat May 15, 2010 4:07 pm

I know what makes an airplane annotated as a "heavy" is the t/o weight is more than 255,000 lbs, correct? But what is the reason behind the "heavy" callsign? Is there a real big difference in wake vortices between a plane that weighs 257,00 lbs and one that weighs 254,000 lbs. One is going to be called a heavy and the other will not, right? Is this callsign simply for advisory reasons for airplanes that are following? Does that make the distance between the two greater? For example, the 757 was for a long time called a heavy, but now is not. I doubt the wake behind it has changed, so does that mean, by rule, you can follow a 757 closer now than when it was a heavy?
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tdscanuck
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RE: Why Is A Heavy Called A Heavy?

Sat May 15, 2010 5:34 pm

Quoting c5load (Thread starter):
I know what makes an airplane annotated as a "heavy" is the t/o weight is more than 255,000 lbs, correct? But what is the reason behind the "heavy" callsign?

Separation due to wake turbulence for the trailing aircraft.

Quoting c5load (Thread starter):
Is there a real big difference in wake vortices between a plane that weighs 257,00 lbs and one that weighs 254,000 lbs.

Not really big, unless there's a particularly bad high-lift implementation, but there is a difference. Much more importantly, you need to draw the line somewhere since the system has to be usable in the practical ATC environment.

Something at the very low end of the heavy class is not realistically any more threatening than something at the very high end of the non-heavy class.

Quoting c5load (Thread starter):
One is going to be called a heavy and the other will not, right?

Generally, yes. I believe, if wake turbulence testing dictated it, an aircraft could be labelled heavy even if it's below the weight threshold.

Quoting c5load (Thread starter):
Is this callsign simply for advisory reasons for airplanes that are following?

For airplanes in trail, and for ATC to setup the correct spacing.

Quoting c5load (Thread starter):
Does that make the distance between the two greater?

Generally, yes, but it depends what's following what.

Tom.
 
AR385
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RE: Why Is A Heavy Called A Heavy?

Sat May 15, 2010 8:43 pm

It has to do with the amount and intensity of the wake turbulence they generate. I´m not sure if it has to do with the weight per se. The 757 is not that big, but it is a big wake turbulence generator. Thus, the call sign "heavy" calls the attention of ATC to give the required separation as well as to anyone following behind on the approach sequence or take off.
 
Caryjack
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RE: Why Is A Heavy Called A Heavy?

Sat May 15, 2010 8:58 pm

Quoting c5load (Thread starter):
One is going to be called a heavy and the other will not, right?

Not necessarily.    The B-757 is an airliner that sits on the fence between the Large and Heavy weight classifications. It generally weighs into the Large class but is able to generate wake turbulence similar to a much larger Heavy. For that reason the 757 has been the subject of much wake turbulence discussion here on A.net. I've attached such a thread.

Why Is 757 A "Heavy"? (by web500sjc Feb 13 2010 in Tech Ops)


I also understand that B-737s are able to generate a disproportionately large wake turbulence and that winglets mitigate this turbulence. I haven't read similar posts concerning winglets on the B-757.
Thanks,  
Cary
 
tdscanuck
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RE: Why Is A Heavy Called A Heavy?

Sat May 15, 2010 9:52 pm

Quoting AR385 (Reply 2):
It has to do with the amount and intensity of the wake turbulence they generate. I´m not sure if it has to do with the weight per se.

To first order, the total vorticity shed is a function of weight, speed, and span only. What differs from aircraft to aircraft is how the vorticity is distributed in the wake.

Tom.
 
71Zulu
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RE: Why Is A Heavy Called A Heavy?

Sat May 15, 2010 11:31 pm

Quoting c5load (Thread starter):
I know what makes an airplane annotated as a "heavy" is the t/o weight is more than 255,000 lbs, correct?

300,000 lbs
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XFSUgimpLB41X
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RE: Why Is A Heavy Called A Heavy?

Sun May 16, 2010 5:20 am

255,000 pounds or greater MTOW capability is the dividing line in the US. Will 257,000 pounds make a huge difference over 255? No.... a line has to be drawn somewhere.

FWIW, no 757 of any type or certification carries the "heavy" designation as of 1 May in the US.
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71Zulu
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RE: Why Is A Heavy Called A Heavy?

Sun May 16, 2010 6:46 am

Quoting XFSUgimpLB41X (Reply 6):
255,000 pounds or greater MTOW capability is the dividing line in the US.

Did they change it again? This says it's now 300,000 lbs.

http://www.faa.gov/documentLibrary/media/Notice/N7110.525.pdf

Quote:
Policy Change. Appendix A is being revised to harmonize FAA weight category standards with those of the International Civil Aviation Organization (ICAO). All aircraft that weigh more than 41,000 pounds, maximum certificated takeoff weight, up to but not including 300,000 pounds, will now be classified as a “Large” aircraft according to FAA standards.

Aircraft capable of takeoff weights of 300,000 pounds or more, whether or not they are operating at this weight during a particular phase of flight, will now be classified as a “Heavy” aircraft according to FAA and ICAO weight classification standards.
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XFSUgimpLB41X
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RE: Why Is A Heavy Called A Heavy?

Mon May 17, 2010 1:29 am

They must have just changed it to 300,000 pounds.

It was 255,000 pounds up until May 1.
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HAWK21M
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RE: Why Is A Heavy Called A Heavy?

Mon May 17, 2010 7:29 am

So wef 8th April 2010
41000 - 300,000lbs = LARGE
300,000lbs + = HEAVY

Any reason stated was to harmonize the same with ICAO.

Is there any more information on its background.

regds
MEL.
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andyinpit
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RE: Why Is A Heavy Called A Heavy?

Mon May 17, 2010 9:08 pm

Quoting 71Zulu (Reply 5):
300,000 lbs

It's back down to 255,000
And no there isn't that much difference, but it's there for when there IS a large difference and there isn't any confusion on when to issue it. Just make it blanket for everything over 255 and you won't forget it.
 
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HAWK21M
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RE: Why Is A Heavy Called A Heavy?

Tue May 18, 2010 10:53 am

Quoting andyinpit (Reply 10):

It's back down to 255,000

Any link to the circular.
regds
MEL.
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andyinpit
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RE: Why Is A Heavy Called A Heavy?

Wed May 19, 2010 6:17 pm

Sorry I dont have a link. Just something I signed off on in our Read and Initial binder. If I can find the change in the 7110.65 I'll let you know
 
KELPkid
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RE: Why Is A Heavy Called A Heavy?

Wed May 19, 2010 8:02 pm

Quoting tdscanuck (Reply 1):
Not really big, unless there's a particularly bad high-lift implementation, but there is a difference.

So are you saying that the 757 has a bad high lift device implementation?   
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KELPkid
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RE: Why Is A Heavy Called A Heavy?

Wed May 19, 2010 8:05 pm

Quoting XFSUgimpLB41X (Reply 6):

255,000 pounds or greater MTOW capability is the dividing line in the US. Will 257,000 pounds make a huge difference over 255? No.... a line has to be drawn somewhere.

FWIW, no 757 of any type or certification carries the "heavy" designation as of 1 May in the US.

So here's one:

The 757-300 max takeoff weight is 272,500 lb. Is it conceivable that a 757-300 can take off as a "heavy" and land with no "heavy" on the callsign?  
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XFSUgimpLB41X
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RE: Why Is A Heavy Called A Heavy?

Fri May 21, 2010 3:30 am

Quoting KELPkid (Reply 14):
So here's one:

The 757-300 max takeoff weight is 272,500 lb. Is it conceivable that a 757-300 can take off as a "heavy" and land with no "heavy" on the callsign?

Please notice that I wrote "capability" i.e. certification, not actual weight. If the airplane is certified above the heavy dividing line, then it is always a heavy regardless of actual weight.

The 757 of all types is no longer a heavy as of the first part of April, as previously stated. Apparently the line moved to 300,000 pounds.
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