c5load From United States of America, joined Sep 2008, 917 posts, RR: 0 Posted (5 years 8 months 4 weeks 1 day 13 hours ago) and read 4328 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"
tdscanuck From Canada, joined Jan 2006, 12710 posts, RR: 80
Reply 1, posted (5 years 8 months 4 weeks 1 day 11 hours ago) and read 4287 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.
AR385 From Mexico, joined Nov 2003, 7478 posts, RR: 41
Reply 2, posted (5 years 8 months 4 weeks 1 day 8 hours ago) and read 4180 times:
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.
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.
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.
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.
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.