Own Separation

Own Separation


The use of own separation means that for some flights, while in controlled airspace, separation is not provided by ATC. For the duration of the clearance, the responsibility for maintaining safe distance from the other aircraft lies with the pilots involved.

Conditions for Application

The use of own separation is described in ICAO Doc 4444 (PANS-ATM), Chapter 5, para 5.9, the key points being:

  • Own separation is applied:
    • upon crew request;
    • in airspace classes D and E only;
    • at or below 10,000 ft;
    • during climb or descent;
  • All flights must be in VMC (they may fly under IFR though);
  • All pilots must agree to the use of own separation;
  • Alternative instructions should be given to IFR flights if it is considered that VMC may not be maintained for the whole duration of the clearance.

Note: The conditions stated above are not exhaustive. Further restriction to the use of own separation may apply if so prescribed in regional air navigation agreements.

Controller Responsibilities

Before issuing a clearance for the use of own separation, the contoller should:

  • Ensure that all conditions are met;
  • Provide the pilots with essential traffic information (since the required separation is likely not to be maintained).

Pilot Responsibilities

If cleared to maintain own separation, the pilots concerned:

  • are responsible for flying at a safe distance from the other aircraft;
  • must inform the controller if they are about to enter IMC.

Safety Issues

There are two major safety issues with the use of own separation:

  • Sometimes the relevant ICAO SARPs are not correctly applied, e.g. because they have not been clearly understood or some circumstances have been misinterpreted.
  • Sometimes own separation is not compatible with ACAS logic.

Own separation is NOT to be used:

  • On controller's initiative;
  • In airspace classes A, B and C;
  • At night;
  • In IMC;
  • Above 10,000 ft;
  • If all aircraft are maintaining their level;
  • If the use of own separation is not agreed by all pilots concerned.

Relevant A&I Events

On 23 July 2011 a Boeing 757 in Class E airspace east of Glasgow in VMC encountered a glider ahead at the same altitude and deviated right to avoid a collision. The glider, climbing in a thermal, had not seen the 757 until it passed during avoiding action. The closest proximity was estimated as 100 metres at the same level as the glider passed to the left of the 757 in the opposite direction. Since the circumstances were considered to have demonstrated a safety critical risk by the UK CAA, an interim airspace reclassification Class D was implemented

On 20 June 2010, a Boeing 737-800 being operated by New Zealand company Pacific Blue AL on a scheduled passenger flight from Auckland to Queenstown lost IFR separation assurance against a Boeing 737-800 being operated by Qantas on a scheduled passenger flight from Sydney to Queenstown whilst both aircraft were flying a go around following successive but different instrument approaches at their shared intended destination. There were no abrupt manoeuvres and none of the respectively 88 and 162 occupants of the two aircraft were injured.

On 27 June 2016, an Airbus A319 narrowly avoided a mid-air collision with an AS532 Cougar helicopter whose single transponder had failed earlier whilst conducting a local pre-delivery test flight whilst both were positioning visually as cleared to land at Marseille and after the helicopter had also temporarily disappeared from primary radar. Neither aircraft crew had detected the other prior to their tracks crossing at a similar altitude. The Investigation attributed the conflict to an inappropriate ATC response to the temporary loss of radar contact with the helicopter aggravated by inaccurate position reports and non-compliance with the aerodrome circuit altitude by the helicopter crew.

On 2 June 2012, a Dornier 328 and a commercially-operated Robinson R44 helicopter came into close proximity within the airport perimeter whilst both were departing from Bern in VMC as cleared. The Investigation attributed the conflict to inappropriate issue of clearances by the controller in a context of an absence of both a defined final approach and take off area and fixed departure routes to the three designated departure points.

On 18 July 2013, an Airbus A319 level at 2000 feet QNH in Class G airspace and being radar vectored towards an ILS approach at Southend in day VMC had a sudden but brief base leg encounter with a paramotor which was not visible on radar and was seen too late for avoiding action to be practicable, before passing within an estimated 50 metres of the A319. The paramotor pilot could not subsequently be traced. The Investigation made a safety recommendation to the UK CAA to review the regulation and licensing of paramotor pilots.

On 5 December 2010 a Boeing 767-300 being operated by Qantas and departing Melbourne for Sydney in day VMC was following a Boeing 737-800 being operated by Virgin Australia which had also just departed Melbourne for Brisbane on the same SID and a loss of prescribed separation occurred. ATC became aware that the 767 was catching up with the 737 but were aware that it was in visual contact and therefore took no action to ensure separation was maintained. No TCAS activation occurred.

On 1 May 2008 an Airbus A320-200 being operated by JetStar on a scheduled passenger flight from Melbourne to Launceston, Tasmania was making a missed approach from runway 32L when it came into close proximity in night VMC with a Boeing 737-800 being operated by Virgin Blue and also inbound to Launceston from Melbourne which was manoeuvring about 5nm north west of the airport after carrying out a similar missed approach. Minimum separation was 3 nm at the same altitude and the situation was fully resolved by the A320 climbing to 4000 feet.

On 21 January 1999, a UK Royal Air Force Tornado GR1 and a private Cessna 152 collided in mid air, at low level in day VMC with the resultant loss of both aircraft and the death of all occupants.

On 5 October 2007, a loss of separation occurred between a Hughes 369 helicopter and a Jodel D150. The incident occurred outside controlled airspace, in VMC, and the estimated vertical separation as the Jodel took avoiding action by descending, was assessed by both pilots to be less than 50 feet.

Related Articles

Further Reading

  • ICAO Doc 4444

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