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Transfer of Control

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

Definition

  • Transfer of responsibility for providing air traffic control service.
  • That action whereby the responsibility for the separation of an aircraft is transferred from one controller to another.

Source: FAA JO 7110.65 (Air Traffic Control)

Description

The transfer of control (TOC) is effected at the transfer of control point. This is usually the point where the flight trajectory crosses the boundary between two adjacent areas of responsibility. This may be a published or a non-published point. An example of the latter is the transfer of control between vertically split sectors where the TOC point position may depend on the vertical speed of the aircraft.

TOC is not to be confused with Transfer of Communication. An important ATM principle is that a controlled flight must be under the control of only one ATC unit at any given time. The objective is to establish a clear criterion for the responsibility for flight safety. It is possible, however, that a flight is in contact with one ATC unit whilst being in another units area of responsibility. This may happen for a number of reasons, e.g.:

  • The pilot was issued a frequency change instruction before crossing the boundary in order to obtain an entry clearance into the next airspace (otherwise an airspace infringement could occur). This is usually done 5-10 minutes before the boundary.
  • The flight was transferred to the next frequency shortly (1-2 minutes) before crossing the boundary. This is a normal procedure to ensure that the receiving controller will be in contact with the pilot at the moment the aircraft enters the airspace. Also, this allows the receiving controller to issue instructions to the aircraft in advance, i.e. to be complied with later.
  • The flight was transferred by mistake (e.g. due to callsign confusion).
  • The flight clipped the airspace of an ATC sector and was therefore transferred directly from the previous sector to the next.
Due to the sector clipping (the flight stays in the sector for a very short time), communication with the flight is transferred directly from Sector A to Sector C.

In all the situations above the flight is in contact with one ATC unit while being in the area of responsibility of another controller. This is a potentially dangerous situation because the controller that communicates with the aircraft may not be fully aware of the traffic situation but has the means to issue instructions to the pilot. Therefore, local procedures usually state that the receiving controller may only do this after an appropriate coordination has been effected (e.g. a Release Procedure).

The flight crew does not actively participate in the TOC. Consequently there is no controller-pilot message exchange, unlike the transfer of communication procedure.

The TOC and the associated procedures are described in Letters of Agreement.

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Further Reading

  • ICAO Doc 4444 PANS-ATM