Wake turbulence category

Weight classification for aircraft for purposes of take-off and landing

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

## Wake turbulence categories

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Since 2020, there are four categories, based on maximum certificated take-off mass:[1]: 4-12 [2]

* Light (L) — aircraft types of 7,000 kg or less.
* Medium (M) — aircraft types more than 7,000 kg but less than 136,000 kg; and
* Heavy (H) — all aircraft types of 136,000 kg or more, with the exception of aircraft types in Super (J) category; and
* Super (J) — aircraft types specified as such in ICAO Doc 8643, Aircraft Type Designators.

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]

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]

### Radio communication

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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

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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)

### Time-based separation minima

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For landing aircraft, time-based separation minima are as follows:[1]: 5-44 [2]

* HEAVY aircraft landing behind SUPER aircraft — 2 minutes
* MEDIUM aircraft landing behind SUPER aircraft — 3 minutes
* MEDIUM aircraft landing behind HEAVY aircraft — 2 minutes
* LIGHT aircraft landing behind SUPER aircraft — 4 minutes
* LIGHT aircraft landing behind HEAVY or MEDIUM aircraft — 3 minutes

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]

### United States of America

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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]

## Wake turbulence groups

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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]

## History

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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.[22]

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.[23] In strong headwinds, reduced time based separation can be used because vortices are dispersed more quickly.[24]

The seven wake turbulence groups were adopted by ICAO in 2020.[2]

## See also

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* Single European Sky ATM Research (SESAR)
* Aircraft approach category

## References

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1. ^ a b c d PANS-ATM Doc 4444, Procedures for Air Navigation Services — Air Traffic Management (PDF) (Sixteenth ed.). ICAO. 2016. ISBN 978-92-9258-081-0. Retrieved 10 February 2023.
2. ^ a b c d e f g h i Amendment No. 9 to the Procedures for Air Navigation Services: Air Traffic Management (Doc 4444). ICAO, 5 November 2020. Better URL needed.
3. ^ a b "Aircraft Type Designators". www.icao.int. Retrieved 10 February 2023.
4. ^ "JO 7360.1H - Aircraft Type Designators – Document Information". www.faa.gov. Retrieved 1 March 2024.
5. ^ "FAA Pilot Controller glossary". www.faa.gov. Retrieved 12 February 2023.
6. ^ "UK Wake Turbulence Categorisation, October 2022". Retrieved 20 July 2023.
7. ^ a b c FAA Order N JO 7110.525, 8 April 2010, archived from the original on 30 October 2019, retrieved 30 October 2019
8. ^ "Concept to Reality – Wake-Vortex Hazard". National Aeronautics and Space Administration. Archived from the original on July 31, 2009. Retrieved July 29, 2011.
9. ^ "FAA Order JO 7110.65Z - Air Traffic Control. Section 5. Radar Separation". www.faa.gov.
10. ^ "Doc 4444-RAC/501: Procedures for Air Navigation Services: Rules of the air and air traffic services, Thirteenth edition" (PDF). ICAO. 1996. Retrieved 12 February 2023.
11. ^ "FAA Advisory Circular: Aircraft Wake Turbulence. Date: 2/10/14 Initiated by: AFS-400 AC No: 90-23G" (PDF). Retrieved 11 February 2023.
12. ^ a b c d e "FAA Letter "Subject: Recategorization (RECAT) of Federal Aviation Administration (FAA) Wake Turbulence Separation Categories at Memphis International Airport (MEM)"" (PDF). faa.gov. Archived (PDF) from the original on 22 January 2018. Retrieved 22 April 2018.
13. ^ a b c d Cheng, Jillian (2016). "The Development of Wake Turbulence Recategorization in the United States" (PDF). AIAA Aviation. 2016–3434: 1–12\. Archived from the original (PDF) on 2017-02-24. Retrieved 2017-03-29.
14. ^ "Revised Wake Turbulence Categories Increase Airport Capacity". flyingmag.com. 31 January 2013. Archived from the original on 27 May 2020. Retrieved 22 April 2018.
15. ^ "Memphis RECAT Increases Capacity Significantly". faa.gov. Archived from the original on 2017-03-30. Retrieved 2017-03-29.
16. ^ "Order JO 7110.123". FAA. August 2, 2016. Archived from the original on October 30, 2019. Retrieved October 30, 2019.
17. ^ a b "RECAT-EU - European Wake Turbulence Categorisation and Separation Minima on Approach and Departure, Edition: 1.1, Edition date: 15/07/2015, Appendix A - Rationale of RECAT-EU design methodology, Par 4" (PDF). EUROCONTROL. Archived (PDF) from the original on 2018-08-05. Retrieved 2018-02-26.
18. ^ "Wake Vortex". eurocontrol.int. EUROCONTROL. Archived from the original on 2014-12-13. Retrieved 2015-01-26.
19. ^ "RECAT-EU". EUROCONTROL. Archived from the original on 2015-04-02. Retrieved 2015-03-26.
20. ^ "RECAT-EU now in use at Paris Charles de Gaulle". www.atc-network.com. 6 September 2016. Retrieved 12 February 2023.
21. ^ "Wake vortex recategorisation (RECAT EU) at Paris-CDG, a first in Europe!". Bernieshoot (in French).
22. ^ "Intelligent Approach | Proven Solution". Intelligent Approach. Archived from the original on 13 April 2024. Retrieved 9 October 2024.
23. ^ "RECAT-EU Pair Wise Separation (Recat 2) and Dynamic Pair Wise Separation (Recat 3)". EUROCONTROL. Archived from the original on 2015-06-05. Retrieved 2015-10-07.
24. ^ "Time based separation". EUROCONTROL. Archived from the original on 2015-04-02. Retrieved 2015-03-20.

## External links

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* FAA Order 7110.65Z Air Traffic Control
* FAA Order 7360.1E Aircraft Type Designators