NUMBER AND TYPE OF AIRCRAFT AND WAKE TURBULENCE CATEGORY
Insert number of aircraft, if more than one (1 or 2 characters) followed by type of aircraft (2 to 4 characters).
The type of aircraft is indicated by the manufacturer’s designator. If no such designator has been assigned, or in the case of formation flights comprising more than one type, insert “ZZZZ” and specify the number(s) and type(s) of aircraft in Item 18 (see below) preceded by “TYP/” (up to 60 characters can be put, for example: TYP/3C182 2C172).
ICAO aircraft type designators are presented in ICAO Doc 8643. You will also find them in SKYbrary, here.
Then add ICAO Wake Turbulence Category (1 character). Options are:
/L – LIGHT, to indicate an aircraft type with a maximum certificated takeoff mass of 7000 kg (15 500 lbs) or less.
/M – MEDIUM, to indicate an aircraft type with a maximum certificated takeoff mass of less than 136 000 kg (300 000 lbs), but more than 7 000 kg (15 500 lbs).
/H – HEAVY, to indicate an aircraft type with a maximum certificated takeoff mass of 136000 kg (300 000 lbs) or more.