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ATC Clearance Delivery

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Category: Ground Operations Ground Operations
Content source: SKYbrary About SKYbrary


The issue of ATC Departure / En Route Clearance for a flight (as distinct from a take off clearance), in particular for an IFR flight.

Potential Risks to Safety

If there is any misunderstanding within the flight crew of the route to be flown after take off, or if any error is made by the flight crew when programming the route to be flown into their FMS, then the risk of Loss of Separation against other traffic or even of Controlled Flight Into Terrain (CFIT), has been increased.

In order for a flight crew to both brief a departure and initial routing and correctly input its details into the aircraft FMS, it is important that the departure clearance is available from ATC in good time prior to engine start / pushback. Both flight crew briefing and FMS input take time and require the full attention of all flight crew members.

It follows from the above that, if changes are made to the departure or initial routing clearance by ATC, the aircraft should be stationary and not under any immediate pressure to move when these are communicated to the crew. Under no circumstances should changes to departure or subsequent flight routing, however minor, be issued at the same time as a take off clearance. This includes all changes to airborne clearances including those arising from change of runway, whether originated by ATC or issued in response to a flight crew request.

Investigation of Accidents and Incidents has often found that the late issue of, or late change to, a departure clearance has been a causal factor in the unwanted outcome.

Mitigation of the Risk - ATC

The existence of appropriate procedures for:

  • the timing of the issue of initial departure clearances - this should preferably be sufficiently ahead of the likely "off blocks" time to allow the flight crew actions which must follow the issue of clearance to be completed before the aircraft first moves.
  • handling a change of departure runway after a departure clearance has been issued.
  • offering a change of departure runway to an aircraft which has already received an initial departure clearance where such a change would have a material effect on the initial airborne routing.

Controllers should be mindful that, even if the operator is a frequent visitor to the airport, the flight crew may not be familiar with the departure procedures, local navigation aids and reporting points - clearances should be passed clearly and and at a steady pace.

Mitigation of the Risk - Aircraft Operation

The existence of appropriate procedures for:

  • Recording of clearances and monitoring of read-back by the flight crew members not operating the radios.
  • Effective cross checking of FMS departure route data entry.
  • Actioning of Initial ATC departure clearances received too late for their input and briefing to be completed before the flight leaves the parking gate.
  • Acceptance and actioning of amendments to initial ATC departure clearances received prior to take off such that the necessary response to them is completed and cross checked prior to take off and the departure re-briefed.

Airport Activity Level

Busy airports, where delays in the departure of an aircraft resulting from necessary flight crew actions caused by a late or changed departure clearance are liable to have awkward consequences, should ensure that their normal procedures include the availability, on request, of a departure clearance at least 10 minutes before pushback from or taxi off stand. These normal procedures should also preclude the issue of pushback or taxi clearance unless a departure clearance has already been issued.

Quieter airports do not need such rigid normal procedures in respect of departure clearances but ATC should still appreciate, and make due allowance for, the time which it may take to set up and brief departure clearances which are issued or altered once an aircraft has begun push back and / or has begun taxiing for take off.

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