Wake turbulence categories and wake turbulence groups are defined by the International Civil Aviation Organization for the purpose of separating aircraft in flight, due to wake turbulence.[1]: 4-12
Since 2020, there are four categories, based on maximum certificated take-off mass:[1]: 4-12 [2]
As of 2023, the only aircraft in Category J is the Airbus A380,[3] with an MTOW of 575 t (1,268,000 lb)). Before its destruction, the single Antonov An-225 (MTOW of 640 t (1,410,000 lb)) was classified by the FAA as Super,[4][5] although it is classified by ICAO as Heavy. The Antonov An-225 and the Antonov An-124 Ruslan are classified by the UK Civil Aviation Authority as Super,[6] although they are classified by ICAO as Heavy.
Most wide-body aircraft are classified as Heavy. Not all aircraft variants of the same type have the same wake turbulence category. The narrow-bodied Boeing 707-100 is Medium but the 707-300 is Heavy.[3]
The word "super" or "heavy" should be included by super or heavy aircraft immediately after the aircraft call-sign in initial radio contact with air traffic service (ATS) units,[2] to warn ATS and other aircraft that they should leave additional separation to avoid this wake turbulence.
Distance-based separation minima for approach and departure are given by ICAO as follows:[1]: 8-13 [2]
| Preceding aircraft | Succeeding aircraft | Distance-based wake turbulence separation minima |
|---|---|---|
| Super | Heavy | 9.3 kilometres (5.0 nmi) |
| Medium | 13 kilometres (7.0 nmi) | |
| Light | 14.9 kilometres (8.0 nmi) | |
| Heavy | Heavy | 7.4 kilometres (4.0 nmi) |
| Medium | 9.3 kilometres (5.0 nmi) | |
| Light | 11.1 kilometres (6.0 nmi) | |
| Medium | Light | 9.3 kilometres (5.0 nmi) |
For landing aircraft, time-based separation minima are as follows:[1]: 5-44 [2]
For departing aircraft, time-based separation minima are more complicated and depend on the runways used, but range from 2 minutes to 4 minutes.[2]
In the United States, the FAA uses a slightly different categorization, adding a block between medium and heavy, labeling aircraft capable of maximum takeoff weights more than 41,000 pounds (19 t) and less than 300,000 pounds (140 t) as "Large".[7]
Of special note here is the narrow-bodied Boeing 757. With a MTOW of 116,000 kilograms (256,000 lb), the 757 is classified as Large.[7] However, after a number of accidents where smaller aircraft following closely behind a 757 crashed, tests were carried out showing the 757 generated stronger wake vortices than a Boeing 767.[8] The rules were changed so that controllers are required to apply special wake turbulence separation criteria specified in paragraph 5-5-4 in the FAA guidelines for aircraft separation, as if the 757 were heavy.[7][9]
In addition to wake turbulence categories, ICAO also specifies wake turbulence groups. These are based on wing span as well as maximum takeoff mass. There are seven groups, A to G.[2]
Wake turbulence groups were introduced to enable reduced separation requirements, although in some cases separation is increased. They are used when permitted by the appropriate air traffic service authority.[2]
Wake turbulence groups enable distance-based separation minima for approach and departure as low as 3 nautical miles. Time-based separation minima are used for separating departing aircraft only. Separation minima range from 80 seconds to 240 seconds.[2]
Wake turbulence categories have existed since at least 1996.[10]
The "Super" category was introduced in 2020 by ICAO, however it had already been introduced by the FAA in 2014.[11]
Wake turbulence groups originated in the United States. In 2012, the FAA authorized Memphis International Airport air traffic controllers to begin applying revised criteria for separation.[12] This initially used six groups of aircraft, primarily based on weight: Super (A380), Heavy, B757, Large, Small+, and Small.[12]
The FAA continued Wake Turbulence Recategorization, or RECAT. In 2013, RECAT was extended from Memphis to 6 other airports.[12] In RECAT Phase I, the groups were replaced with six groups, A to F, based on weight, certificated approach speeds, and wing characteristics, with special consideration given to aircraft with limited ability to counteract adverse rolls.[12][13] These groups were named "Super", "Upper Heavy", "Lower Heavy", "Upper Large", "Lower Large", and "Small".[13] In some cases, separation was increased but in other cases it was reduced.[12] The revised spacing between these groups was shown to increase airport capacity.[14] The FAA estimated an increase in capacity of 15% at Memphis, and average taxi time for FedEx (Memphis' largest carrier, with about 500 operations per day in 2012) aircraft was cut by three minutes.[15]
RECAT Phase II was a continuation of the RECAT program that focused on a larger variety of aircraft (123 ICAO type designators that make up more than 99% of US air traffic movements based on 32 US airports), as opposed to the 61 aircraft comprising 85% of operations from 5 US and 3 European airports that were used in RECAT Phase I.[citation needed] The wake separations in RECAT Phase II were not defined by wake turbulence groups, but individual pairs of make-model-series aircraft types (e.g. Boeing B747-400 leading Airbus A321). In the US, automation does not yet[when?] exist to allow air traffic controllers to utilize this pairwise separation matrix. Instead, RECAT Phase II takes advantage of the underlying matrix to redefine the RECAT Phase I-type categories (i.e. Categories A–F, with an additional Category G) for individual TRACONs (terminal radar approach control). This allows efficiency gains over RECAT I because it takes the fleet mix – which aircraft fly most often – into account for each site, rather than doing a global optimization for the US national airspace system as a whole.[13] RECAT Phase II went operational on August 3, 2016, at Southern California TRACON and associated towers.[16]
In RECAT Phase III, which was in development as of 2016, atmospheric conditions were taken into account.[13]
In Europe, the programme to increase runway throughput by introducing new wake turbulence groups was called RECAT-EU. With a database of over 100,000 wake measurements, EUROCONTROL also developed six wake turbulence groups. The change was partly prompted by the development of the Airbus A380.[17][18] The previous three wake turbulence categories were increased to six, by splitting Medium and Heavy into pairs, and adding a Super Heavy category for the Airbus A380.[19] Capacity gains of up to 8% were achieved.[17]
RECAT-EU was initially deployed at Paris Charles de Gaulle and Paris Le Bourget airports in 2016.[20][21]
RECAT-EU for arrivals and departures was successfully deployed by NATS at London Heathrow Airport in March 2018.[citation needed]
In RECAT-2, the six categories were augmented by individual pair-wise separation, based on the characteristics of the lead and following aircraft types. RECAT-3 further augments this by using real-time data including ground-based measurements of wake decay.[22] In strong headwinds, reduced time based separation can be used because vortices are dispersed more quickly.[23]
The seven wake turbulence groups were adopted by ICAO in 2020.[2]