I once had an international operations instructor screaming at me at the top of her lungs when I asked "where are we?" in response to her question about weather deviation procedures. Lost on many is that if you are in radar contact and talking to an air traffic controller, you should state your intentions and start from there. If you are not in radar contact and your only means of communication is via an ARINC radio operator or CPDLC, well then things change.
Most of these procedures are given in ICAO Doc 4444 §15.2, and are repeated below.
The basic concepts for contingencies are described in Special Procedures for In-flight Contingencies in Oceanic Airspace.
Everything here is from the references shown below, with a few comments in an alternate color.
ICAO Doc 4444 §15.2.4
Note.— The following procedures are intended for deviations around adverse meteorological conditions.
220.127.116.11.1 When weather deviation is required, the pilot should initiate communications with ATC via voice or CPDLC; rapid response may be obtained by either:
a) stating "WEATHER DEVIATION REQUIRED" to indicate that priority is desired on the frequency and for ATC response; or
b) requesting a weather deviation using a CPDLC lateral downlink message.
18.104.22.168.2 When necessary, the pilot should initiate the communications using the urgency call “PAN PAN” (preferably spoken three times) or by using a CPDLC urgency downlink message.
22.214.171.124.2 The pilot shall inform ATC when weather deviation is no longer required, or when a weather deviation has been completed and the aircraft has returned to its cleared route.
126.96.36.199.1 The pilot should notify ATC and request clearance to deviate from track or ATS route, advising, when possible, the extent of the deviation requested. The flight crew will use whatever means are appropriate (i.e. voice and/or CPDLC) to communicate during a weather deviation.
Note.— Pilots are advised to contact ATC as soon as possible with requests for clearance in order to provide adequate time for the request to be assessed and acted upon.
188.8.131.52.2 ATC should take one of the following actions:
184.108.40.206.3 The pilot should take the following actions:
Note.— The provisions of this section apply to situations where a pilot needs to exercise the authority of a pilot-in-command under the provisions of Annex 2, 2.3.1.
If the aircraft is required to deviate from track or ATS route to avoid adverse meteorological conditions and prior clearance cannot be obtained, an ATC clearance shall be obtained at the earliest possible time. Until an ATC clearance is received, the pilot shall take the following actions:
Note.— If, as a result of actions taken under the provisions of 220.127.116.11.1, the pilot determines that there is another aircraft at or near the same flight level with which a conflict may occur, then the pilot is expected to adjust the path of the aircraft, as necessary, to avoid conflict.
|Originally cleared track or ATS route centre line||Deviations
≥9.3 km (5.0 NM)
|DESCEND 90 m (300 ft)
CLIMB 90 m (300 ft)
|CLIMB 90 m (300 ft)
DESCEND 90 m (300 ft)
ICAO Doc 4444 - Air Traffic Management, 16th Edition, Procedures for Air Navigation Services, International Civil Aviation Organization, October 2016
ICAO Doc 4444 - Air Traffic Management, 16th Edition, Amendment 9, Procedures for Air Navigation Services, International Civil Aviation Organization, November 5, 2020
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