This paper proposes IFATCA Policy regarding the Weather Deviation Procedure that has been developed for use in the Asia Pacific Region in conjunction with the implementation of 50 NM Lateral Separation Minima. The full ICAO title of this document is the Weather Deviation Procedure in the Regional Supplementary Procedures (Doc. 7030) for the Asia Pacific Region.

ICAO is preparing to give final approval to a Weather Deviation Procedure that will be implemented concurrently with a reduction in lateral track separation minima to 50nm. Although this procedure has been developed over a long period of discussion, there are still serious questions regarding the liability of ATCOs operating within this procedure.

The entire proposed procedure is included as Appendix A of this paper. The section that is generating concerns is 4.1, h, iii, a-c. That section defines the actions that are to be taken by the controller in a situation where the aircrew is able to establish two-way communications with ATC and in which the controller is unable to grant a clearance to deviate because of conflicting traffic.

Section 4.1, h, iii, a-c states:

While ICAO acknowledges that the intention for this procedure is that a pilot who follows the ATC provided suggestion is doing so as a function of the pilot’s emergency authority, it became evident at a recent meeting of the ISPACG (Informal South Pacific ATC Co-ordinating Group) that some States are still unclear as to this intention and view the operation of this procedure as the pilot complying with instructions from ATC.

The following procedures are intended to provide guidance. All possible circumstances cannot be covered. The pilot’s judgement shall ultimately determine the sequence of actions taken and ATC shall render all possible assistance.

If the aircraft is required to deviate from track to avoid weather and prior clearance cannot be obtained, an ATC clearance shall be obtained at the earliest possible time. In the meantime, the aircraft shall broadcast its position (including the ATS route designator or the track code, as appropriate) and intentions, on frequency 121.5 MHz at suitable intervals until ATC clearance is received.

The pilot shall advise ATC when weather deviation is no longer required, or when a weather deviation has been completed and the aircraft has returned to the centreline of its cleared route.

Obtaining Priority From ATC When Weather Deviation is Required

When the pilot initiates communications with ATC, rapid response may be obtained by stating “WEATHER DEVIATION REQUIRED” to indicate that priority is desired on the frequency and for ATC response.

The pilot still retains the option of initiating the communications using the urgency call “PAN-PAN ” 3 times to alert all listening parties of a special handling condition which will receive ATC priority for issuance of a clearance or assistance.

Actions to Be Taken

Pilot-controller Communications Are Established:

Pilot notifies ATC and requests clearance to deviate from track, advising when possible the extent of the deviation expected.

Pilot-controller Communication Not Established Or Revised ATC Clearance Not Available:

If contact cannot be established or revised ATC clearance or advisory is not available and deviation from track is required to avoid weather, the pilot shall take the following actions:

• If possible, deviate away from an organised track or route system;
• Broadcast aircraft position and intentions on frequency 121.5 MHz at suitable intervals stating: flight identification (operator call sign), flight level track code or ATS route designator, and extent of deviation expected;
• Watch for conflicting traffic both visually and by reference to TCAS (if equipped);
• Turn on aircraft exterior lights;
• Deviations of less than 10nm or operations within COMPOSITE AIRSPACE, aircraft should REMAIN at ASSIGNED Altitude.

Other Cases :

• When the aircraft is approximately 10nm from track, initiate an altitude change based on the following criteria:

Pilot Memory Slogan: “East right up, West right down”

• When returning to track, be at assigned FL or altitude, when the aircraft is within approximately 10nm of centerline;
• If contact was not established prior to deviating, continue to attempt to contact ATC to obtain a clearance. If contact was established, continue to keep ATC advised of intentions and obtain Essential Traffic Information;
• ATC takes one of the following actions:
  • If there is no conflicting traffic in the horizontal dimension, ATC will issue clearance to deviate 60m track;
  • If there is conflicting traffic in the horizontal dimension, ATC separates aircraft by establishing vertical separation (2,000 feet above FL290, 1,000 feet below FL290) and issues clearance to deviate from track;
  • If there is conflicting traffic in the horizontal dimension and ATC is unable to establish vertical separation, ATC shall:
    • Advise the pilot that standard separation cannot be applied; and
    • Provide essential traffic information for all affected aircraft; and
    • If possible, suggest a course of action. ATC may suggest that the pilot climb or descend to a contingency altitude (1,000 feet above or below that assigned if operating above FL 290; 500 feet above or below that assigned if operating at or below FL290).

Standard separation not available, deviate at Pilot’s discretion; suggest climb to flight level three six zero parallel traffic zero miles north at flight level three five zero; report deviation complete.