When the ceiling is less than 450 m (1 500 ft); or
When the ground visibility is less than 5 km.
Above FL 200;
At transonic and supersonic speeds;
More than 180 km seaward from the shore line within controlled airspace.
Over the congested areas of cities, towns or settlements or over an open- air assembly of persons at a height less than 300 m (1 000 ft) above the highest obstacles within a radius of 600 m (2000 ft) from aircraft;
Elsewhere than as specified in 5a) above, at a height less than 150 m (500 ft) above the ground or water.
TABLE ENR 1.2
Altitude spectrum |
Airspace class |
Flight visibility |
Distance from ACFT to cloud |
At and above 3 050 M (10 000 FT) AMSL | C D E G | 8 KM |
1 500 M horizontal and 300 M (1 000 FT) vertical distance from cloud |
Below 3 050 M (10 000 FT) AMSL and above 900 M (3 000 FT) AMSL, or above 300 M (1 000 FT) above terrain, whichever is higher | C D E G | 5 KM |
1 500 M horizontal and 300 M (1 000 FT) vertical distance from cloud |
At and below 900 M (3 000 FT) AMSL or 300 M (1 000 FT) above terrain, whichever is higher | C D E | 5 KM |
1 500 M horizontal and 300 M (1 000 FT) vertical distance from cloud |
At and below 900 M (3 000 FT) AMSL or 300 M (1 000 FT) above terrain, whichever is higher | G | 5 KM* |
Clear of cloud and ground (water) in sight |
When the height of the transition altitude is lower than 3 050 M AMSL, FL100 should be used in lieu of 3 050 M (10 000 FT).
(*) When so prescribed by Civil Aviation Authority of Viet Nam:
Lower flight visibilities to 1 500 M may be permitted for flights operating:
At speeds that, in the prevailing visibility, will give adequate opportunity to observe other traffic or any obstacles in time to avoid collision; or
In circumstances in which the probability of encounters with other traffic would normally be low, e.g in areas of low volume traffic and for aerial work at low levels.
Helicopters may be permitted to operate in less than 1 500 M flight visibility, if manoeuvred at a speed that will give adequate opportunity to observe other traffic or any obstacles in time to avoid collision.
When operated within Classes C and D airspace;
When forming part of aerodrome traffic at controlled aerodromes; or
When operated as special VFR flights.
If flight plan was submitted, communicate the necessary changes to be effected to its current flight plan; or
When so required by Annex 2, Chapter 3, section 3.3, submit a flight plan to the appropriate air traffic services unit and obtain a clearance prior to proceeding IFR when in controlled airspace.