Dozens of flights from and to airports in northern and central Vietnam have been affected by hazy climate in recent times, according to local air firms.

Many flights arriving at and departing from Noi Bai International Airport in Hanoi on Saturday morning were delayed or had their routes re-directed due to thick fog, local air firms said.

It was not until 9:00 am that weather conditions turned better, but negative influences from such conditions were undeniable, local carriers said.

Canceling and delaying flights not only affect passengers but also inflict severe damage on an air firm’s business, a spokesperson of an aviation company said.

Although the firm is required to pay no reimbursement to customers for delaying or canceling flights due to bad weather, it has to pay such compensation for any delayed flight that follows, the spokesperson added.

Vietjet, a Vietnamese budget airline, said that seven of its flights at the airport had their departure time delayed for one hour on average, rendering 26 connection flights to fall behind schedule.

National carrier Vietnam Airlines also admitted that it had altered flight routes and schedules for over 40 flights from and to the airport for safety purposes.

Three of the flights from London, Paris, and Frankfurt were diverted to touch down at Da Nang International Airport in the central city of Da Nang instead of Noi Bai as scheduled, the airline announced.

Pham Viet Dung, director of Vietnam Air Traffic Management Corporation, said that thick fog hazing the airport significantly reduced visibility to 200-300 meters, forcing all flights heading to the airdrome to divert as the instrument landing system (ILS) could not support pilots at such a distance.

According to Airservices Australia, a corporate Commonwealth entity providing aviation-involved services, ILS is a highly accurate radio signal navigation aid used by pilots landing at an airport when there is poor weather and/or low visibility.

All flights departing from Noi Bai also had to wait for better conditions to take off in safety, Dung said.

Yesterday, the foggy weather also affected flights to Phu Bai Airport in Hue, the capital city of Thua Thien-Hue, a coastal province in the central region, the two carriers said as two of their flights from Ho Chi Minh City to Hue had to land at Da Nang International Airport.

Passengers booking the affected flights are entitled to alternative flights when the weather turns better, the aviation firms said, adding that they can either demand refunds or change their tickets.

On Friday, thick fog also enveloped Cat Bi International Airport in the northern city of Hai Phong and Dong Hoi Airport in the north-central province of Quang Binh, causing several flights from and to the airports to be delayed, diverted, or even canceled.

According to Dung, visibility at the two airports improved as fog density declined on Saturday evening.

In Vietnam, come March and April, thick fog and poor weather conditions tend to occur in the northern and central regions.