Loss of Separation - ATCO-induced Situations

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Article Information
Category:	Loss of Separation
Content source:	SKYbrary
Content control:	EUROCONTROL

Description

Loss of separation between aircraft sometimes occurs as a result of action taken (or not taken) by the ATCO.

Effects

• Loss of separation from other aircraft may result in collision or the need for flight crew to take visual avoiding action at close range to avoid one.

• Injury, especially to cabin crew or passengers, may result from any unusual manoeuvres to avoid a collision.

• Injury to the occupants of an aircraft, especially Cabin Crew, may also result from wake vortex turbulence encounter.

Defences

• Standard Operating Procedures, in the ATSU, which detail procedures to be followed to reduce the chance of loss of separation.
• Onboard aircraft equipment designed to warn of potential collision with other aircraft (ACAS/TCAS).
• Ground-based equipment designed to warn of potential collision with other aircraft: Short Term Conflict Alert (STCA).

For ABC123 - the controller spots both PQR265 and XYZ312 but overlooks DEF763

Typical Scenarios

• Flight clearance does not provide adequate separation from other traffic.

• ATCO does not detect developing potential conflict.

• Avoiding action issued is too late or inadequate to provide safe separation.

• Instruction not received or not understood by intended recipient due to breakdown in air-ground communications.

Contributory Factors

• Volume of traffic;
• Military traffic operating out of the segregated area in civil airspace
• Flight crews (military or civil) unfamiliar with the applicable rules and procedures in a particular volume of airspace;
• Failure to pass an IFR aircraft timely traffic information about VFR aircraft in its vicinity;
• Issue of a VFR clearance in airspace where the only prescribed traffic separation is IFR against IFR when the ability of the VFR aircraft to comply with its clearance and maintain an effective visual lookout may be compromised by weather conditions;
• ATCO Workload
• Interruption or Distraction
• Fatigue

Solutions

• Improve standard of ATCO training, especially in:
  • Air-ground communications safety;
  • Loss of situation awareness;

• Provide more and improved ATC safety nets, e.g. STCA.

Related Articles

• Accident and Serious Incident Reports: LOS contains a number of examples of ATCO induced loss of separation.
• Minimum Hours in Position

Further Reading

HindSight Articles:

• HindSight1 Analysis of an AIRPROX between a B737 and an A340;
• HindSight2 Loss of Separation - an Incident at Paris/Orly;
• HindSight3 Loss of separation: The Blind Spot;
• HindSight4 Loss of Separation - A Lesson for the Instructor;
• HindSight5 Loss of Separation - TCAS and STCA - Not Just Anagrams
• HindSight6 Loss of Separation - Mid-Air Collisions, Elephants, and Systems Approaches