Study Route Clearances and Associated Requirements

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Study Route Clearances and Associated Requirements

49TH ANNUAL CONFERENCE, Punta Cana, Dominican Republic, 12-16 April 2010

WP No. 85

Study Route Clearances and Associated Requirements

Presented by TOC


TOC first looked at flight planning since a safe and secure flight plan system is essential to route clearances. Within Europe the CFMU IFPS controls all aspects of flight planning. Elsewhere the ICAO flight plan system is in use. There are differences between Europe and the rest of the world as to how airways clearances are issued. This difference makes the implementation of any new policy a significant challenge The practice of oceanic clearances in the NAT region is examined and the inherent pitfalls of the NAT organised track system and the associated downstream clearance. CPDLC is seen as providing solutions to some of the problems highlighted in this paper.

Two new policy recommendations are made in this paper.


1.1 The move to increased automation and Datalink will require a comprehensive review of all route clearances and their associated requirements. The issues examined include:

1) Issue of a route clearance for the whole of the flight (common in many parts of the world) or clearance for only part of the flight as is common in Europe.

2) Issue of more than one clearance at a time (such as Oceanic Clearance in NAT in addition to current clearance) whereas only one clearance is used elsewhere.

3) The work study considers controllers, pilots and automations expectations of requirements and what is done when the clearance is changed. Both Voice and Datalink communications should be considered and the resulting procedures be consistent and globally harmonised


2.1 In examining the above item TOC has looked at the following areas. No IFATCA policy exists on route clearances. To globally harmonize route clearance procedures will be difficult due to the fact of different methods used in Europe and elsewhere as illustrated in item 1 of the introduction. To be able to issue an air traffic control clearance an air traffic control unit must have access to a flight plan on which the air traffic control clearance will be based. This paper will therefore first address Flight Planning and thereafter address route clearances and related issues.

2.2 Flight Plan

2.2.1 ICAO Annex 11

ICAO defines a flight plan under the following headings:

“Flight Plan: Specified information provided to air traffic service units, relative to an intended flight or portion of a flight of an aircraft.”

“Filed Flight Plan: The flight plan as filed with an ATS unit by the pilot or a designated representative, without any subsequent changes.”

“Current Flight Plan: The flight plan, including changes, if any brought about by subsequent clearances.”

“Repetitive Flight Plan: A flight plan related to a series of frequently recurring, regularly operated individual flights with identical basic features, submitted by an operator for retention and repetitive use by ATS units.”

2.2.2 The flight plan represents one of the single most important messages submitted to ATS and the manner in which it is handled will determine whether the flight it refers to will have a trouble free passage through the ATC network.

2.2.3 The filed flight plan can be subjected to many changes before the flight becomes active and it is extremely important that the flight plan is correctly processed. The flight plan must be submitted for distribution to adjacent ATS units in the correct flight plan format otherwise it may fail to be processed by automated ATM systems. Should such a situation arise the adjacent ATS unit may not have a copy of the flight plan when the flight becomes active and as result the flight could be delayed or may not receive the routeing or flight level requested.

2.2.4 Flights plans can be routinely delayed, changed or cancelled as circumstances dictate and it is important that flight planners adhere to correct procedures at all times in relation to flight plans.

2.2.5 The ICAO model flight plan form is available to submit a flight plan and an example of this form is available in Doc.4444 PANS-ATM. For regularly occurring flights a Repetitive Flight Plan can be submitted. This flight plan is processed in the same way as an individually filed flight plan and is subject to the same conditions if delayed, changed, amended or cancelled as necessary.

2.2.6 IFATCA policy on Flight Plans

Since Frankfurt 1989, IFATCA has had policy on Flight Plans:

ATS 3.1 Replacement Flight Plans

Where owing to ATFM restrictions upon the initial flight plan route, the initial plan is cancelled and a new plan filed there is a need to ensure that the replacement flight plan can be identified as such. Procedures to achieve this have been in use in the European Region for several years but have caused difficulties to states in other regions.

IFATCA Policy is:

ICAO should review, as soon as possible, world-wide procedures and systems for amending or replacing flight plans or flight plan information, to ensure that such system and procedures exist, and that amended or replacement flight plans, or portion thereof are easily identifiable to control personnel.


2.2.7 Within the European Region a flight plan processing system has been developed namely the Integrated Initial Flight Plan Processing System (IFPS).

The IFPS is a centralised flight plan processing and distribution service that has been established under the authority of the Eurocontrol Central Flow Management Unit (CFMU) and it covers that part of the EUR Region known as the IFPZ. An IFPS users manual is available and is a comprehensive document that provides all users of the IFPS an easy to access reference document.

The manual is intended to contain all the necessary procedures and information in order for users to be able to construct, transmit or when necessary to correct, flight plan and associated update messages. Procedures for the distribution of such messages after processing by the IFPS are also described.

As with the ICAO global flight plan system, correct and accurate application of the procedures contained within the IFPS users manual is essential to the achievement of consistent flight plan data among all relevant actors in the flight planning process. The IFPS is a very effective system and works very well within the European Region where it is employed.

In tandem with the IFPS system is the Flow Management system of the CFMU It is the Air Traffic Flow and Capacity Management (ATFCM).

ATCFM Users Manual, Section 3:

“3.1 Objectives

ATFCM is a service that is enhancing ATFM with the objective of managing the balance of demand and capacity by optimising the use of available resources and coordinating adequate responses, in order to enhance the quality of service and the performance of the ATM system.”

ATCFM has, according to the CFMU Handbook, 3 phases:

  • Strategic Flow Management
  • Pre-Tactical Flow Management
  • Tactical Flow Management

2.3 Air Traffic Control Clearances

2.3.1 ICAO Doc 4444 PANS-ATM

“Air traffic control clearance. Authorization for an aircraft to proceed under conditions specified by an air traffic control unit.

Note1.- For convenience, the term “air traffic control clearance” is frequently abbreviated to “clearance” when used in appropriate contexts.

Note2.- The abbreviated term “clearance” may be prefixed by the words “taxi”, “departure”, “en route”, “approach” or “landing” to indicate the particular portion of flight to which the air traffic control clearance relates.”

2.3.2 Every movement of an aircraft in controlled airspace is subject to a clearance and as can be seen every constituent unit of Air Traffic Control is required to issue a clearance. Each clearance has a “clearance limit”.

ICAO Annex 11 Air Traffic Services, Chapter 1 – Definitions:

“Clearance limit. The point to which an aircraft is granted an air traffic control clearance.”

2.3.3 ICAO Annex 11 Air Traffic Services, Chapter 3 – Air Traffic Control Service:

“3.7 Air traffic control clearances

Air traffic control clearances shall be based solely on the requirements for providing air traffic control service.

3.7.1 Contents of clearances An air traffic control clearance shall indicate:

a) aircraft identification as shown in the flight plan;

b) clearance limit;

c) route of flight;

d) level(s) of flight for the entire route or part thereof and changes of levels if required;

Note.— If the clearance for the levels covers only part of the route, it is important for the air traffic control unit to specify a point to which the part of the clearance regarding levels applies whenever necessary to ensure compliance with a) of Annex 2.

e) any necessary instructions or information on other matters such as approach or departure manoeuvres, communications and the time of expiry of the clearance.”


3.7.3 Read-back of clearances and safety-related information The flight crew shall read back to the air traffic controller safety-related parts of ATC clearances and instructions, which are transmitted by voice. The following items shall always be read back:

a) ATC route clearances;

b) clearances and instructions to enter, land on, take off on, hold short of, cross and backtrack on any runway; and

c) runway-in-use, altimeter settings, SSR codes, level instructions, heading and speed instructions and, whether issued by the controller or contained in ATIS broadcasts, transition levels.

2.3.4 ICAO Annex 11 Air Traffic Services, Chapter 3 – Air Traffic Control Service:

“3.7.4 Coordination of clearances

An air traffic control clearance shall be coordinated between air traffic control units to cover the entire route of an aircraft or a specified portion thereof as follows. An aircraft shall be cleared for the entire route to the aerodrome of first intended landing:

a) when it has been possible, prior to departure, to coordinate the clearance between all the units under whose control the aircraft will come; or

b) when there is reasonable assurance that prior coordination will be effected between those units under whose control the aircraft will subsequently come.“

2.3.5 ICAO Annex 11 Air Traffic Services, Chapter 1 – Definitions:

“Downstream clearance. A clearance issued to an aircraft by an air traffic control unit that is not the current controlling authority of that aircraft.”

2.3.6 ICAO Annex 11 Air Traffic Services, Chapter 3 – Air Traffic Control Service:

“ When coordination as in has not been achieved or is not anticipated, the aircraft shall be cleared only to that point where coordination is reasonably assured; prior to reaching such point, or at such point, the aircraft shall receive further clearance, holding instructions being issued as appropriate. When prescribed by the appropriate ATS authority, aircraft shall contact a downstream air traffic control unit, for the purpose of receiving a downstream clearance prior to the transfer of control point.”

2.4 Enroute

2.4.1 Flights that cross the North Atlantic oceanic airspace are required to obtain an oceanic clearance prior to reaching the oceanic entry point. This is a requirement even though the aircraft will probably have received a clearance to destination via FPL route prior to departure.

2.4.2 Flights that for example exit the Atlantic eastbound must receive an onward clearance through European airspace. It is now quite a regular occurrence for such a flight to still have 12 or 13 hours of the flight time remaining. In a busy ATC environment it can be impractical and too time consuming to issue a route clearance all the way to the destination of this flight. This is an area where CPDLC could be of benefit. When a trans Atlantic flight is cleared on an oceanic track other than the track filed in the flight plan such flights regularly arrive at the European or North American landfall and do not have a flight plan route beyond the landfall. This is being caused by a failure to issue the onward clearance to aircraft when their flight plan route is changed. This leads to an increased workload for the controller handling this traffic and increased complexity and uncertainty in the event of a communication failure.

2.4.3 There is also an issue when NERS (North Atlantic European Routing Scheme) are in place for the concerned NAT traffic that may request a route change but because of the NERS requirements must adhere to the assigned route.

2.4.4 Route and flight plan problems have been created when flow management units issue route changes for aircraft exiting the NAT. The aircraft concerned are only issued with the re-clearance on exiting the NAT airspace leading to increased controller and pilot workload.

2.4.5 The CFMU in issuing a directive to ATC not to clear an aircraft at a level other than the requested level in the flight plan fails to acknowledge that the first responsible of ATC is to provide separation and an orderly flow of traffic is subservient to this.

2.4.6 The use of a separate oceanic clearance results in the pilots being in receipt of two clearances from different ATC units at the same time, and the clearances may be inconsistent.

2.4.7 With regard to downstream clearances issued on VHF, for example oceanic clearances, cockpit procedures dictate that both pilots must listen to the clearance being issued. This creates a conflict with the requirement to listen to the ATC operational frequency at all times.


3.1 Flight planning and route clearances are inextricably linked. It is essential that correct procedures are strictly followed in relation to flight planning. Failure to cancel an old flight plan when submitting a new one could lead to a situation where ATC may have one flight plan and the flight crew have another.

3.2 In the documentation TOC has studied, data link and voice communication are treated in the same manner as regards adherence to ICAO Standards and Recommended Practices. TOC has no evidence to suggest that Datalink is creating any problems in relation to the issues that are being discussed.

3.3 If an ATC unit changes the route of a flight then it should ensure that the new route rejoins the current flight plan route. A more widespread use of CPDLC could help solve some of the route clearance problems highlighted in this paper.

3.4 IFATCA should continue to study and collect more information on the issue.


It is recommended that:

4.1 IFATCA policy is:

A route clearance issued to an aircraft should be to destination.

and is included on page 3 2 3 2 of the IFATCA Technical and Professional Manual.

4.2 IFATCA policy is:

If an ATC unit changes a route then that ATC unit should ensure that the new route rejoins the current flight plan route.

and is included on page 3 2 3 2 of the IFATCA Technical and Professional Manual.


ICAO Annexes.


Eurocontrol CFMU Users Manual.

IFATCA Technical and Professional Manual.

Last Update: September 29, 2020  

April 16, 2020   240   Jean-Francois Lepage    2010    

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