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I'm surprised this hasn't been asked before but I couldn't find it by searching.

For separating arriving aircraft, ICAO PANS-ATM-Doc 4444 Air Traffic Management refers to aircraft as "LIGHT", "MEDIUM" or "HEAVY" but I cannot find any definition of what makes an aircraft fall into any particulate category.

I would of expected a limit on MTOW for each category, does such a definition exist or is it more of an informal definition?

5.8.2 · Arriving aircraft

5.8.2.1 Except as provided for in 5.8.l.l a) and b), the following separation minima shall be applied.

5.8.2.l.l The following minima shall be applied to aircraft landing behind a HEAVY or a MEDIUM aircraft:

a) MEDIUM aircraft behind HEAVY aircraft- 2 minutes;

b) LIGHT aircraft behind a HEAVY or MEDIUM aircraft- 3 minutes.

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Section 4.9.1.1 of ICAO PANS-ATM-Doc 4444 Air Traffic Management defines LIGHT, MEDIUM & HEAVY aircraft for the purpose of wake separation:

4.9.1 Wake turbulence categories of aircraft

4.9.1.1 Wake turbulence separation minima shall be based on a grouping of aircraft types into three categories according to the maximum certified take-off mass as follows:

a) HEAVY (H) — all aircraft types of 136,000kg or more;

b) MEDIUM (M) — all aircraft types less than 136,000kg but more than 7,000kg; and

c) LIGHT (L) — aircraft types of 7,000kg or less.

4.9.1.2 Helicopters should be kept well clear of light aircraft when hovering or while air taxiing.

Note 1.— Helicopters produce vortices when in flight and there is some evidence that, per kilogram of gross mass, their vortices are more intense than those of fixed-wing aircraft.

Note 2.— The provisions governing wake turbulence minima are set forth in Chapter 5, Section 5.8, and Chapter 8, Section 8.7.3.

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The FAA answers this question here: Weight Class

Weight Class Weight class is based are assigned by APO130 based on the TFMS observed aircraft codes. There are 6 categories -- (A) Heavy, (B) B757, (C) Large Jet, (D) Large Commuter, (E) Medium, (F) Small.

(A) Heavy: Any aircraft weighing more than 255,000 lb such as the Boeing 747 or the Airbus A340;

(B) B757: Boeing 757 all series;

(C) Large Jet: Large jet aircraft weighing more than 41,000 and up to 255,000 lbs such as the Boeing 737 or the Airbus A320;

(D) Large Commuter: Large non-jet aircraft (such as the Aerospatiale/Alenia ATR-42 and the Saab SF 340), and small regional jets (such as the Bombardier Canadair Regional Jet), weighing more than 41,000 and up to 255,000 lbs;

(E) Medium: Small commuter aircraft including business jets weighing more than 12,500 up to 41,000 lbs such as the Embraer 120 or the Learjet 35; and

(F) Small: Small, single, or twin engine aircraft weighing 12,500 lbs or less such as the Beech 90 or the Cessna Caravan.

Unknown; refers to unspecified equipment.

"Light" Aircraft follows the same definition as "Small" in the above text.

Wake turbulence is no joke - you can feel it if you come in behind a larger aircraft even several minutes after it lands, and often even if you stay above its glide path and land beyond its touchdown point, as you should.

There was a Grumman Tiger landing at my local airport that didn't pay attention, ignored the tower's "caution wake turbulence" warning, and got flipped inverted and subsequently crashed as a result of wake turbulence from a UH-60 military helicopter that had departed several minutes prior. The pilot, very fortunately, walked away but the aircraft was ruined.

Note that even though helicopters are not mentioned in your post - any helicopter leaves persistent rotor wash and you should be extremely cautious and wait several minutes before attempting to takeoff or land anywhere a helicopter has been.

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  • $\begingroup$ This question is about ICAO L/M/H categories, not about FAA classifications $\endgroup$ – J. Hougaard Feb 13 '17 at 19:57
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Let me add the proposed Super category. According to Wiki and this article:

ICAO mandates separation minima based upon wake turbulence categories (WTC) that are, in turn, based upon the Maximum Take Off Mass (MTOW|MTOM) of the aircraft.

These minima are typically categorised as follows:

  • Light (L)– MTOW of 7,000 kilograms (15,000 lb) or less;
  • Medium (M)– MTOW of greater than 7,000 kilograms, but less than 136,000 kilograms (300,000 lb);
  • Heavy (H)– MTOW of 136,000 kilograms (300,000 lb) or greater.

A fourth category is currently being taken into consideration by ICAO:¹

  • Super (J)– Refers only to the Airbus A380

Even though the resolution to add the "Super" category is still under consideration, both the FAA (see below) and EUROCONTROL have already implemented guidelines concerning the Airbus A380.

(emphasis mine)

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