Wake vortex

Existing ICAO Wake Vortex separation rules were implemented over 40 years ago. In recent years these have, in some respect, become outdated leading to many States introducing their own changes to the ICAO scheme.

In Europe there are many variations which have implications both for safety and capacity. The reason the ICAO rules have not previously been updated is that the means to do this was not available. Any change would require the completion of a full safety case which demonstrates that change is safe to implement.

Due to the lack of measuring technology it would not have been possible to support the safety arguments with data and therefore the safety of the proposed change could not be proven. However, with the development of measuring technology and the increased understanding of the nature of wake vortices, it is now possible to update the ICAO wake vortex provisions and also develop new advanced wake turbulence related procedures. These will have a positive effect on safety and capacity and could significantly reduce airport delays.


Airbus A380

With the development of the Airbus A380 one of the main challenges for ATM was the development of wake turbulence separations before the aircraft entered service. The issue was that there was no proven methodology available at the start of the project. In July 2003 a European led A380 Steering Group was established with representatives from EUROCONTROL, JAA (EASA), AIRBUS, FAA, NASA and ICAO.

Its tasks were to:

  • Select methodologies for evaluation of A380 wake turbulence;
  • Assess A380 wake turbulence in comparison to other aircraft of the Heavy category;
  • Establish recommendation for A380 wake turbulence separation to ICAO.

Recommendations are based on a Safety Case and Safety Assessment Report produced by the Working Group, in accordance to EUROCONTROL Safety Regulatory Requirement 4 (ESARR 4). This work resulted in an initial ICAO State Letter detailing separation requirement of 10NM for all aircraft following the A380.

A second State Letter was issued by ICAO in Oct. 2006 with reduced interim separations pending more data collection and a third State Letter was issued July 2008 with further reduced separations.

Work is continuing with the analysis of Airbus flight test data to determine if further separation reductions are possible.


Re-categorisation of the ICAO Wake Turbulence Separation Minima (RECAT)

The aim of RECAT is to increase capacity at airports by redefining wake turbulence categories and their associated minimum separations.

Today’s ICAO separations based solely on Maximum Take Off Weight (MTOW) and aircraft are allocated into one of three categories - Heavy, Medium or Light. It is recognised that the current Medium category as defined by ICAO is too large, 136000kg – 7000kg and encompasses aircraft from the size of the B757 down to aircraft types such as the BEECH 1900. Because the separations are defined based on worst case in each category, this leads to over separation in many instances.

As a result of this ICAO asked EUROCONTROL and the FAA to investigate the possibility of re-categorising aircraft and developing new wake turbulence separation standards. The EUROCONTROL / FAA Phase 1 work has resulted in a new methodology based not only on MTOW but also wingspan, speed and rolling moment. The initial work is in an advanced stage and will be completed by 2013.


Wind dependent separations

The Time Based Separation (TBS) - Transitional Step

The scope of the TBS Transitional Step is to propose a change in the current ATM procedures that will enable ATC controllers to apply a fixed reduction of the ICAO wake turbulence distance-based radar separation minima between wake turbulence separated aircraft pairs in specified headwind conditions.

The level of operational applicability and benefits will depend on local wind conditions and runway orientation.

New system requirements will remain at minimum level. A 10kt headwind (still to be confirmed) plus a buffer (this will depend on the local accuracy of the Met forecast data) may allow for this reduction which will only apply to aircraft on final approach (4000 ft or below).

A Concept of Operations (CONOPS) has been produced and a Safety Assessment is currently in production. The CONOPS will require a final update, specifically defining the required headwind threshold, depending on the results of the Safety Assessment. The Safety Assessment will be supported by more than 5 years of scientific work, and data collection using LIDAR, showing that close to the ground, the turbulence will make the vortex decay faster, and on the glide path, the wake will move backwards and therefore below the glide path.


Crosswind Operations (CROPS)

Cross Wind Operations (CROPS) is a change to the procedure, very similar to the Time Based Separation for the purposes of a reduction of wake separation on final approach in specified crosswind conditions.

A 5kt crosswind (still to be confirmed) plus a buffer (this will depend on the local accuracy of the Met forecast data) may allow for this reduction which, as for Time Based Separation, will only apply to aircraft on final approach (4000 ft or below).

CROPS will initially concentrate on approaches but will later look to extend the application to departures. The CROPS project is at the same stage of development as the Time Based Separation. In the case of CROPS, however, the Safety Assessment will demonstrate that above the agreed wind threshold any wake vortices will be transported out of the flight path of a following aircraft.


Contact the Wake Vortex team by email

Phone: +32 2 729 5173

Wake Vortex
Airport Operations
Network Management
Rue de la fusée 96
B-1130 Brussels

Share this