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RECAT - Wake Turbulence Re-categorisation2

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Article Information
Category: Wake Vortex Turbulence Wake Vortex Turbulence
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Definition

Wake Turbulence Re-categorisation, or Wake RECAT, is the safe decrease in separation standards between certain aircraft.

Description

The ICAO wake vortex separation rules were based solely upon aircraft weight, categorised as Heavy, Medium or Light. While safe, in some respects, they gradually became outdated and lead to over-separation in many instances. This, in turn, diminished airport capacity and caused unnecessary traffic delays increasing costs, fuel burn and emissions. As an example, both the Boeing 747 and the Boeing 767 are categorised by ICAO as "Heavy" aircraft. Whilst the 4nm traditional separation distance, applied between two "heavies", is appropriate when the 767 is following the 747, in the reciprocal case, this separation is excessive. To safely reduce the separation minima between a given aircraft pair, whether on departure or on final approach, both the wake vortex generated by the leader and the following aircraft’s resistance to it have to be taken into consideration.

Background

The ICAO categorisation of aircraft into three weight dependent groups had, for some time, been considered inadequate by many National Aviation Authorities and this led to some regional variation in the categories and separation standards. The introduction of the Airbus A380 and the associated wake vortex turbulence concerns lead to an ICAO supervised joint study with experts from Airbus, the FAA, EUROCONTROL and JAA/EASA. The primary focus of the study was the A380 and the resulting Airbus A380 Wake Vortex Guidance was published in 2008. However, the supporting programme of over 180 hours of innovative flight testing including back to back comparative testing of different aircraft, cruise wake encounter tests, and ground and airborne LIDAR wake measurements, also led to the introduction of the RECAT programme.

After years of extensive, collaborative research between EUROCONTROL, the FAA, their research facilities and the aviation industry, the experts concluded that the required separation between certain aircraft could be safely decreased. Research proved that, in addition to weight, other aircraft characteristics – such as speed and wingspan – also affect the strength of the wake generated as well as the following aircraft’s reaction to that wake. Using that information, aircraft were re-assigned to one of six new groups (A through F). Generally, only the largest aircraft (such as the Airbus A380 and Antonov 225) were assigned to the A category. Other heavy aircraft, such as the Boeing 747, Airbus A330/A340 were placed in the B category and the "lower heavy", C category included e.g. the Boeing 767, Airbus A310 and DC-10/MD-11. The medium weight aircraft were divided into "upper", D category (e.g. the A320 Family and the NG variants of the B737 Series) and "lower", E category (e.g. the "classic" variants of the Boeing 737 series and most of the regional aircraft). The last, F category included all light aircraft as well as most (but not all) business jets and some regional airliners (e.g. Saab 340).

In 2020 ICAO adopted a slightly different recategorization which was based on the same principles (maximum take off mass and wingspan). It divided the aircraft types into 7 groups (A through G). The new group emerged from splitting the medium weight aircraft into three groups insted of just two. Again, some medium aircraft were placed together with the light aircraft group.

Re-categorisation

The ICAO categorization based on weight and wingspan is as follows:

  • GROUP A — aircraft types of 136 000 kg or more, and a wing span less than or equal to 80 m but greater than 74.68 m;
  • GROUP B — aircraft types of 136 000 kg or more, and a wing span less than or equal to 74.68 m but greater than 53.34 m;
  • GROUP C — aircraft types of 136 000 kg or more, and a wing span less than or equal to 53.34 m but greater than 38.1 m;
  • GROUP D — aircraft types less than 136 000 kg but more than 18 600 kg, and a wing span greater than 32 m;
  • GROUP E — aircraft types less than 136 000 kg but more than 18 600 kg, and a wing span less than or equal to 32 m but greater than 27.43 m;
  • GROUP F — aircraft types less than 136 000 kg but more than 18 600 kg, and a wing span less than or equal to 27.43 m;
  • GROUP G — aircraft types of 18 600 kg or less (without wing span criterion).

Note: The application of this categorization is subject to the approval of the appropriate ATS authority.

Examples of aircraft types belonging to each of these groups are provided in the table below. The lists is not exhaustive.

Group A Group B Group C Group D Group E Group F Group G
AIRBUS A-380-800 ANTONOV An-124 Ruslan AIRBUS A-300-600 AIRBUS A-318 BOEING 717-200 ATR ATR-72-201 ATR ATR-42-300/320
(...) AIRBUS A-330-200 AIRBUS A-300 AIRBUS A-319 BOEING 737-200 BOMBARDIER Challenger 600 ATR ATR-42-500
AIRBUS A-330-300 AIRBUS A-310 AIRBUS A-320 BOEING 737-300 BOMBARDIER Regional Jet CRJ-100 FAIRCHILD DORNIER 328
AIRBUS A-340-300 BOEING 707-300 AIRBUS A-321 BOEING 737-400 BOMBARDIER Regional Jet CRJ-700 EMBRAER Brasilia
AIRBUS A-340-500 BOEING 757-200 ANTONOV An-12 BOEING 737-500 EMBRAER ERJ 170-100 BEECH 400 Beechjet
AIRBUS A-340-600 BOEING 757-300 BOEING 737-600 BOMBARDIER Dash 8 Q400 EMBRAER ERJ-145 RAYTHEON BAe-125-700/800
AIRBUS A350-900 BOEING 767-200ER BOEING 737-700 EMBRAER ERJ 190-100 GULFSTREAM AEROSPACE Gulfstream 4 BRITISH AEROSPACE Jetstream 32
BOEING 747-400 (international, winglets) BOEING 767-300ER BOEING 737-800 (...) (...) BRITISH AEROSPACE Jetstream 41
BOEING 747-8 BOEING 767-400 BOEING 737-900 GATES LEARJET Learjet 35
BOEING 777-200 / 777-200ER BOEING C-135 Stratolifter LOCKHEED C-130 LEARJET Learjet 60
BOEING 777-300 MCDONNELL DOUGLAS DC-10 MCDONNELL DOUGLAS MD-81 SAAB 340
BOEING 777-200LR and 777-F MCDONNELL DOUGLAS MD-11 MCDONNELL DOUGLAS MD-90 PIAGGIO P-180 Avanti
BOEING 787-8 Dreamliner ILYUSHIN Il-76 TUPOLEV Tu-204 CESSNA 650 Citation 3/6/7
(...) TUPOLEV TU-95 (...) CESSNA 525 CitationJet
(...) C180
DASSAULT Falcon 10
(...)

Separation Criteria

Under standard ICAO criteria, wake turbulence separation, for arrival or departure, are as follows:

Preceding Aircraft Following Aircraft Minimum Separation
SUPER HEAVY 5.0 NM
SUPER MEDIUM 7.0 NM
SUPER LIGHT 8.0 M
HEAVY HEAVY 4.0 NM
HEAVY MEDIUM 5.0 NM
HEAVY LIGHT 6.0 NM
MEDIUM LIGHT 5.0 NM

In some regions, there are special standards for aircraft following a Boeing 757.

When applying the wake turbulence groups A-G, the required separation is as depicted in the following table.

An empty field indicates that the minimum surveillance based separation applies
Leader/Follower Group B Group C Group D Group E Group F Group G
Group A 4 NM 5 NM 5 NM 6 NM 6 NM 8 NM
Group B 3 NM 4 NM 4 NM 5 NM 5 NM 7 NM
Group C 3 NM 3.5 NM 4.5 NM 6 NM
Group D 4 NM
Group E 4 NM

For time based separation on departure, the following values, in seconds, apply.

Leader/Follower Group B Group C Group D Group E Group F Group G
Group A 100 s 120 s 140 s 160 s 160 s 180 s
CAT B 100 s 120 s 120 s 140 s
CAT C 80 s 100 s 100 s 120 s
CAT D 120s
CAT E 100s

Benefits

Immediate benefits of the recategorization, in terms of runway capacity and operational efficiencies include:

  • Peak period runway throughput can increase by 5% or more depending on airport traffic mix.
  • For an equivalent volume of traffic, recategorized spacing results in a reduction of the overall flight time for each affected aircraft reducing fuel burn, emissions and operating costs.
  • Due to more efficient departure and arrival spacing, recategorization allows a more rapid recovery from adverse conditions or a runway change.
  • In airspace trending towards saturation, such is the case in Europe, the projected fleet renewal is trending towards a greater percentage of larger aircraft. With the use of recategorization, this evolution will actually further enhance runway capacity.

Implementation

The first implementation of RECAT separation standards occurred in the United States at Memphis , Tennessee in November 2012. FedEx, the major carrier at Memphis, has reported substantial efficiencies and savings due to the RECAT programme. The bulk of the FedEx fleet serving Memphis is made up of CAT-C (old ICAO "heavy") aircraft. The new separation standards result in reducing the old 4 mile requirement to Minimum Radar Separation of 2.5 to 3 miles and save the Company both time and fuel. The FAA has reported an airfield capacity increase of as much as 15 percent at peak hours and FedEx has demonstrated an average sector time reduction of about 5 minutes and a fuel savings approaching $1.8 million per month. Since 2012, RECAT procedures have been also introduced at several other major US airports including Louisville International Airport, Cincinnati North Kentucky, Atlanta/Hartsfield-Jackson International, Houston Intercontinental and most of the New York City area airports. A diagram depicting implementation can be found here by scrolling to the bottom of the page and selecting "Wake Re-Categorization Phase 1" in the "Capabilities" box.

The first European implementation of the RECAT separation standards is scheduled for Paris/Charles de Gaulle Airport at the end of 2015.

Related Articles

Further Reading

ICAO

  • Doc 4444 PANS-ATM

EUROCONTROL

FAA

US Department of Transport

Airbus

  • Wake Votrices, C. Lelaie, Airbus Safety First Magazine No. 21, pp. 42-50, January 2016.