heavy airlines?

Question

what does "heavy" mean when airlines refer to it?

Answer 1

SIZE of aircraft,
amount of engines
and the like.

Answer 2

Aircraft are categorised by ICAO according to the amount of wake turbulence they produce. Because wake turbulence is generally related to the weight of an aircraft, these categories are based on weight—aircraft with a maximum certificated take-off weight of 300,000 lb (136,000 kg) or more are classed as Heavy, those between 15,500 lb and 300,000 lb (7,000 kg and 136,000 kg) are classed as Medium, and those below 15,500 lb (7,000 kg) are classed as Light. Due to their weight, all current wide-body aircraft are categorised as Heavy.

The wake turbulence category is used to guide the separation of aircraft—a Heavy category aircraft will require greater separation behind it than a Medium category, which in turn requires more separation than a Light category. In some countries, such as the USA, it is a requirement to suffix the aircraft's call sign with the word "heavy" when communicating with ATC in the Terminal Radar Area. If the aircraft is on an ARTCC (Center Freq), they are not required to say "heavy" at the end of the callsign. For example, flight UAL342 operated by United Airlines using a wide bodied aircraft would use the call sign "United 342 Heavy" while in the USA.

Answer 3

It means they have an MTOW (max take off weight) of 300,000 lbs or more. Heavy aircraft have to leave an extra amount of space behind them because of their wake turbulence. That's why if you have ever listened to air traffic controllers they say for exapmple, "American 12 heavy." They are required to say that so other aircraft in the area are aware and can adjust accordingly.