Guidance concerning Air Navigation in and above the NAT MNPSA
DEVIATIONS AROUND SEVERE WEATHER
If the aircraft is required to deviate from track to avoid weather (e.g. thunderstorms), the
pilot should request a revised clearance from ATC and obtain essential traffic information prior to deviating. This is the case even when a pilot expects to have to deviate by a relatively small distance (e.g. less than 10 NM). If, however, if such prior ATC clearance cannot be obtained, the procedures described below should be adopted and in the meantime efforts should be continued to obtain an appropriate ATC clearance.
If possible, deviate away from the organised track or route system;
Establish communications with and alert nearby aircraft broadcasting, at suitable intervals: aircraft identification, flight level, aircraft position (including ATS route designator or the track code) and intentions, on the frequency in use and on frequency 121.5 MHz (or, as a back-up, on the VHF inter-pilot air-to-air frequency 123.45 MHz);
Watch for conflicting traffic both visually and by reference to ACAS/TCAS (if equipped);
Turn on all aircraft exterior lights.
For deviations of less than 10 NM, aircraft should remain at the level assigned by ATC;
For deviations of greater than 10 NM, when the aircraft is approximately 10 NM from track, initiate a level change of 300 ft.
If flying generally Eastbound (i.e. a magnetic track of 000° to 179°) and deviating left (ie north) of track then descend 300 ft; if, however, deviating right (i.e. south) of track then climb 300 ft.
If flying generally Westbound (i.e. a magnetic track of 180° to 359°) and deviating left
e. south) of track then climb 300 ft; if, however, deviating right (i.e. north) of track then descend 300 ft.
Deviations>19 km (10 NM)
LEFT RIGHT LEFT RIGHT
DESCEND 90 m (300 ft) CLIMB 90 m (300 ft) CLIMB 90 m (300 ft) DESCEND 90 m (300 ft)
Route centre line track EAST (000° 179° magnetic)
WEST (180° 359° magnetic)
When returning to track, regain the last assigned flight level, when the aircraft is within approximately 10 NM of centre line.
The pilot should inform ATC when weather deviation is no longer required, or when a
weather deviation has been completed and the aircraft has returned to the centre line (or previously adopted SLOP Offset) of its cleared route.
ICAO established a worldwide programme in 2008 for collecting data on wave vortex
encounters. Most wake vortex encounters occur in terminal operations and indeed this is where the aircraft type wake categorization scheme is used to regulate separations. The ICAO programme was aimed at reviewing the categorization scheme in light of the recent introduction into service of a new type of very large aircraft.
NAT Doc 007