This follows a directive, No 2690/CT-CHK, signed by Dinh Viet Thang, Deputy Head of the Civil Aviation Authority of Vietnam, on July 25.

The move aims to ensure the safety of flights after recent crashes of foreign airplanes that were later tied to weather issues.

Thang said airlines were also asked to follow special flight procedures during storms.

In case of complicated weather, including fog, airlines were required to choose a second reserve airport for landing, outside of the area affected by poor weather, he said.

Under the directive, airlines were banned from taking off and landing when weather conditions resulted in poor visibility, cloud ceilings and wind speeds that were above allowed standards.

Airlines were also not allowed to make landing approaches more than twice.

In case of bad weather, flight crews are to ask for advice from air-traffic controller agency to receive better assessments of weather developments before making the second landing approach.

If a flight crew cannot properly evaluate weather developments, they should remain on standby mode or shift to their reserve airports, Thang said.

The crews were ordered to immediately report to air-traffic controllers when their planes flew through bad weather.

Then, the agency could promptly send warnings to other planes, which were headed into the same area or scheduled to fly along the same path, he added.

Also, the aviation agency ordered domestic airports in Cat Bi, Vinh, Phu Cat, Pleiku, Lien Khuong and Buon Me Thuot, which were equipped with street lighting systems, to make observations of weather conditions and send a routine aviation weather report every 30 minutes.

Meanwhile, international airports at Noi Bai, Danang and Tan Son Nhat were required to send Terminal Area Forecast (TAF) – a concise statement of expected meteorological conditions at an airport during 24 hour periods, along with amended forecasts, as of August 1.