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Loss of Separation - Pilot-induced Situations

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Category: Loss of Separation Loss of Separation
Content source: SKYbrary About SKYbrary


Loss of separation between aircraft sometimes occurs as a result of an aircraft deviating from the cleared track without clearance.

Loss of separation may be either in a vertical or a horizontal plane, or both.


  • Loss of separation from other aircraft may result in collision. This is especially likely when RVSM procedures are in force.
  • Injury, especially to cabin crew or passengers, may result from violent manoeuvres to avoid collision with other aircraft or the ground.

  • High levels of stress for the pilots and controllers involved, which may lead to reduced performance.


  • Onboard aircraft equipment designed to warn of potential collision with other aircraft (TCAS).
  • Ground-based equipment designed to warn of potential collision with other aircraft: (STCA).

Typical Scenarios

  • Flight deviates from cleared track or level without clearance:
    • Due to pilot inattention, equipment malfunction or the mis-setting of aircraft equipment;
    • To avoid a visually-perceived loss of separation from another aircraft;
    • To avoid severe weather if IFR or to remain in VMC if VFR.
  • Pilot fails to follow ATC clearance or delays their actioning of an accepted clearance.
  • Pilot receives a TCAS RA but fails to follow it correctly.

Contributory Factors

  • Weather (e.g. thunderstorm activity).


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