Expect winter flight delays

We are now in deep winter in Nepal, and although there is mostly clear weather in the mountains, airports in the Tarai cities have poor visibility due to fog mixed with cross-border pollution.

Several international airlines that had started flights to Bhairawa have suspended operations because of low visibility due to smog, and the Instrument Landing System (ILS) not being operational because the signal goes over Indian territory.

Kathmandu and Pokhara also suffer from low visibility due to inversion layer in the valleys that trap smog, but the visibility generally improves by mid-morning. In addition, Kathmandu airport has limited operations by 10 hours from 10pm to 8am every day till April, and this increases congestion. 

All these factors add up to flight delays and cancellations, which can be a source of frustration, especially when a quick search on Google shows clear skies at the destination. However, the reasons behind these disruptions often go beyond the weather conditions. 

At Kathmandu’s domestic departure hall Buddha Air has installed live webcams of the airports it serves, and on most winter mornings passengers can see for themselves that the runway visibility at Tarai airports is almost zero.

One important safety protocol that can lead to delays is the ‘three-airport rule’ which requires that the departure airport, the destination airport, and a third alternative airport all meet safety standards, including adequate visibility and weather conditions suitable for takeoff and landing.

If any of these three locations are affected by poor visibility, thick fog, or low clouds, a flight may be delayed or canceled even if weather apps on passenger smartphones show sunny weather. 

“We understand passengers are irritated by long delays, but these are factors beyond our control and the go, no-go decisions are taken with safety as the primary consideration,” says Dipendra Karna of Buddha Air.

Google's weather updates offer a generalised forecast and don’t provide the level of detail needed for aviation safety. For example, airlines use specialised reports like METARs (Meteorological Aerodrome Reports) and TAFs (Terminal Aerodrome Forecasts), which offer real-time, precise details about factors such as wind, humidity, visibility, and temperature at airports. 

Buddha Air and Nepal’s other domestic airlines rely on these advanced weather systems to assess conditions and maintain safety standards, Karna says. 

Winter months often bring dense fog, particularly in regions like Nepal, where fluctuating humidity can lead to poor visibility. Fog, even in small amounts, can be dangerous, particularly during the crucial phases of takeoff and landing. 

While advanced technology like ILS and RNAV assist pilots in low-visibility conditions, these systems have their limits, and a minimum visibility threshold must be met to ensure safe operations. In Nepal’s mountainous terrain, where many airports have shorter runways and complex approaches, even a slight reduction in visibility can result in cancellations.

Weather-related delays can also have a ripple effect throughout the day’s flight schedule. A flight delayed by Kathmandu’s smog in the morning, for example, can cause a chain reaction, affecting flights into the evening and night. 

Airlines must adjust schedules to accommodate refueling, maintenance, and other logistical needs, which means even if the weather improves later in the day, delays may still persist. Keeping passengers informed about the reason for delays is critical, and Buddha Air crew and ground staff are trained to communicate this promptly and accurately.

“Understanding the reasons behind these decisions can help alleviate some of the frustration associated with travel disruptions,” adds Karna. “When delays occur, it’s important to stay informed and flexible, especially during the winter months when weather-related challenges like fog are more common.”