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Why Is A Heavy Called A Heavy?  
User currently offlinec5load From United States of America, joined Sep 2008, 917 posts, RR: 0
Posted (4 years 2 months 1 week 5 days 11 hours ago) and read 3479 times:

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?


"But this airplane has 4 engines, it's an entirely different kind of flying! Altogether"
15 replies: All unread, jump to last
 
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 1, posted (4 years 2 months 1 week 5 days 10 hours ago) and read 3438 times:

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.


User currently offlineAR385 From Mexico, joined Nov 2003, 6130 posts, RR: 30
Reply 2, posted (4 years 2 months 1 week 5 days 7 hours ago) and read 3331 times:
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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.


MGGS
User currently offlineCaryjack From United States of America, joined May 2007, 305 posts, RR: 0
Reply 3, posted (4 years 2 months 1 week 5 days 6 hours ago) and read 3321 times:

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


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (4 years 2 months 1 week 5 days 5 hours ago) and read 3297 times:

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.


User currently offline71Zulu From United States of America, joined Aug 2006, 3060 posts, RR: 0
Reply 5, posted (4 years 2 months 1 week 5 days 4 hours ago) and read 3255 times:

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



The good old days: Delta L-1011s at MSY
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4190 posts, RR: 37
Reply 6, posted (4 years 2 months 1 week 4 days 22 hours ago) and read 3150 times:

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.



Chicks dig winglets.
User currently offline71Zulu From United States of America, joined Aug 2006, 3060 posts, RR: 0
Reply 7, posted (4 years 2 months 1 week 4 days 20 hours ago) and read 3123 times:

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.



The good old days: Delta L-1011s at MSY
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4190 posts, RR: 37
Reply 8, posted (4 years 2 months 1 week 4 days 2 hours ago) and read 2932 times:

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

It was 255,000 pounds up until May 1.



Chicks dig winglets.
User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 9, posted (4 years 2 months 1 week 3 days 20 hours ago) and read 2867 times:

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.



Think of the brighter side!
User currently offlineandyinpit From United States of America, joined Sep 2007, 320 posts, RR: 0
Reply 10, posted (4 years 2 months 1 week 3 days 6 hours ago) and read 2751 times:

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.


User currently offlineHAWK21M From India, joined Jan 2001, 31667 posts, RR: 56
Reply 11, posted (4 years 2 months 1 week 2 days 16 hours ago) and read 2639 times:

Quoting andyinpit (Reply 10):

It's back down to 255,000

Any link to the circular.
regds
MEL.



Think of the brighter side!
User currently offlineandyinpit From United States of America, joined Sep 2007, 320 posts, RR: 0
Reply 12, posted (4 years 2 months 1 week 1 day 9 hours ago) and read 2456 times:

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

User currently offlineKELPkid From United States of America, joined Nov 2005, 6343 posts, RR: 3
Reply 13, posted (4 years 2 months 1 week 1 day 7 hours ago) and read 2429 times:

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?   



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineKELPkid From United States of America, joined Nov 2005, 6343 posts, RR: 3
Reply 14, posted (4 years 2 months 1 week 1 day 7 hours ago) and read 2427 times:

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?  



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlineXFSUgimpLB41X From United States of America, joined Aug 2000, 4190 posts, RR: 37
Reply 15, posted (4 years 2 months 1 week ago) and read 2270 times:

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.



Chicks dig winglets.
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