Between VFR and IFR in Nepal's airspace

With the onset of spring, surface visibility has improved in Kathmandu and Tarai cities, reducing the notorious delays in domestic flights on trunk routes in Nepal.

However, spring also brings its own complications. Wildfires in central Nepal have reduced visibility this week in Kathmandu, and rain and snow is forecast nationwide this weekend.

Whenever this happens and runway visibility drops below a certain minimum, Nepal’s aviation rules require pilots to fly planes according to instrument flying rules (IFR).

IFR involves strict adherence to approach and departure procedures in which pilots need familiarisation for each airport they fly in and out of. In India, many domestic flights in January were delayed by six hours, some more than nine hours, because the visibility was below minimum due to fog in north Indian airports.

Angry passengers recorded videos of brawls with airline staff which quickly went viral. While the inconvenience to passengers was real, there was nothing the airlines could do about poor visibility.

Fortunately, in Nepal domestic airlines have done a good job in explaining to the flying public about weather issues. And although there are groans and some complaints, most passengers tend to understand.

What has helped is better communication from cabin and ground staff to passengers informing about approximate delay times. Nepal’s biggest domestic airline, Buddha Air, has installed large tv monitors at departure terminals showing live webcam footage from major airports so passengers can see for themselves what conditions are like at the destination.

What compounds the problem at Kathmandu compared to international airports elsewhere is that when pilots are directed by air traffic control to fly IFR, they have to make a VOR-DME instrument approach from the south with a 7 minute separation between aircraft.

When the weather is good, domestic airlines are allowed to fly according to visual flight rules (VFR) and they land from either the north (20) or south (02) ends of the runway and there are minimal delays.  

But on days when the visibility is poor, like it was on Friday, planes have to make long holds, or are not given clearance to take off from the departing airports itself. Planes waiting to fly out of Kathmandu also have to wait at the apron or the taxiway for the long line of planes to land.

A pilot selects an ideal set of rules depending on the weather conditions of the day. The Visual Meteorological conditions (VMC) determine which set of rules is to be planned. This flying modality follows the ‘see and avoid’ principle. A VFR pilot relies on what they can see outside, maintain proper orientation and separation with other aircraft for takeoff, landing and en route flying.

VFR flying is ideal for busy airspaces, recreational flights, sightseeing, and short-distance travel in good weather conditions. Small aircraft are flown VFR because the aircraft covers a smaller area and there is better visibility from the cockpit.

Domestic airlines flying to remote area airports like Lukla, Jomsom, Dolpo, Phaplu, Jumla or Simikot are mandatorily required to fly only VFR because of high terrain. Buddha Air flies mostly trunk routes which have instrument landing procedures, but for airports like Tumlingtar, Surkhet and for Mt Everest Sightseeing the flights need to be VFR.  

The Civil Aviation Authority of Nepal has set criteria for VFR flying to be 8km horizontal separation and at a height of 3,050m above sea level. No cloud must be present 1,500m horizontally or 300m vertically from the aircraft. The aircraft must fly at an altitude of 300m over terrain. In the mountains, it must maintain a 600m distance from the ground.

IFR flying is conducted when weather conditions do not permit VFR flying, such as in low visibility, clouds, or adverse weather conditions.

“One of the main reasons for flight delays and redirection is due to the weather,” says Upendra Lal Shrestha, Senior Quality Assurance Engineer of Buddha Air. “Before flight, the Operation Control Center (OCC) team provides a brief overview of the in-route and the destination weather.”