A while back, I viewed a tweet about an Air Traffic Control (ATC) conversation in New York, where JFK ATC got a little bit confused about an aircraft type. Â American Airlines (AA) Flight 32 was incorrectly called a â€œheavyâ€ aircraft, likely because for so long that flight was operated by a Boeing 767-200. Â Ever since AA debuted their new Airbus A321 on the LAX-JFK route, this flight no longer needs to use the “heavy” designation, but that didn’t stop the ATC staff from using old habits. Â It made me question, at what point does an aircraft become â€œheavyâ€?
When aircraft are approaching or departing an airport, they must use special designations to help avoid the wake turbulence from other aircraft. Â Larger aircraft, like a 767 or an A340, need more space behind them to prevent the wake vortices generated by the larger wing span from impacting other aircraft. Â The bigger the aircraft, the longer the distance.
The dangers are real, as all over the world a number of incidents have occurred that can be attributed to a wake vortex. Â From the crash of an XB-70 in the 60’s to some involving more modern aircraft in the last 10 years (including an A380 in Sydney).
Wake turbulence from an aircraft is caused by a number of factors; the two biggest are jet-wash and the wingtip vortices. Â As the wing tip passes through the sky, it can dramatically affect the air around it for a long duration, causing disrupted air for following aircraft. Â Jet-wash, caused by the engines of the aircraft, does not last as long; however, it can be more violent.
Want to know how bad jet-wash can affect an aircraft? Just look at the scene in Top Gun when Maverick loses control and has to eject, killing his Radar Intercept Officer, Goose. Â That crash was caused by the jet-wash from the proceeding aircraftâ€™s engines. Â Definitely not something you would want to go through on a regular basis, right?
Although the FAAÂ doesn’tÂ necessarily follow ICAO rules, the two do have very similar designations. Â The â€œheavyâ€ designation goes to any aircraft with a takeoff weight of 300,000lb or more, even if they are not operating at that level. Â So, for instance, any 777 departing or arriving an airport, even if below that 300,000lb weight, would still need to use the “heavy” designation. Â Any aircraft below 300,000lb would be categorized as â€œlargeâ€ (though ATC isn’t required to use that term ). Â
There is one aircraft that doesn’t quite make it to the “heavy” designation that needs extra space, and that is the Boeing 757. Â Since it has many characteristics of a heavy, but without the takeoff weight of itâ€™s much larger cousins, it is given the same separation but isn’t required to use the designator. Â But how much separation do they need to give? Â Hereâ€™s a handy little guide:
Minimum radar separation
So you may notice an extra category in the above table? Â The â€œsuperâ€ designation belongs to one aircraft only – the A380. Â With the advent of the â€œwhalejetâ€ came a requirement for a new code, as the A380 needs a much larger separation distance, especially from smaller aircraft. Â I know I wouldn’t want to get caught in that wake turbulence.
So next time you’re at an airport or listening in to ATC and hear the flights using the terms “heavy” or “super”, you can know that those terms have an underlying meaning to help keep you and other passengers safe in the air. Â Plus, it gives you and idea how long until that next aircraft is going to pass overhead, and you can impress your friends with your random AvGeek knowledge.