Own Separation
Own Separation
Description
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 29 January 2025, a Mitsubishi CRJ700, operating a scheduled airline flight on short final approach to land on runway 33 at Ronald Reagan Washington National in night VMC collided with a U.S. Army Sikorsky UH60 helicopter. The helicopter was on a training flight using a designated restricted-height route which intersected the runway 33 extended centreline. The UH60 had requested and received ‘own separation’ from the other traffic. This route had a maximum height of 200 feet agl but no lateral limits. Both aircraft were destroyed, and there were no survivors.
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.
Further Reading
- ICAO Doc 4444
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