An investigation into the reasons behind the crash of the ill-fated US-Bangla flight BS-211, which has claimed least 51 lives so far, might take a year to complete, Civil Aviation Authority of Bangladesh (CAAB) said yesterday. Though CAAB is not the main investigating body here—rather the Civil Aviation Authority of Nepal (CAAN) is—CAAB Chairman Air Vice Marshal M Naim Hassan told reporters yesterday at his office that such investigation “usually” takes that much time.

According to rules set out under the Convention on International Civil Aviation, the primary role in the probe goes to the country where a crash occurs, but the states where the aircraft was registered, where the airline was based and where the plane was designed can all have a role.

“Completing the investigation of such air accidents may take a year or even more,” said the CAAB Chairman when asked when the real reason of the disaster could be known. A flurry of reasons has already been given as possible causes for the crash of the US-Bangla plane at Kathmandu airport on Monday ranging from pilot fatigue to confused communication with air-traffic controllers about which end of the runway the flight would land.

Speculation over reasons for the crash, which killed 51 of the 67 passengers and four crew members on board, has been rife after a tape of the radio conversation between the captain of the flight, Abid Sultan, and officials at Tribhuvan  International Airport in Nepal was uploaded to YouTube.

The Bangladeshi airline and airport authorities in Kathmandu have blamed each other for the tragedy, after it emerged that there was confusion over landing instructions. However, experts concerned said the real reason behind the flight disaster

would not be known unless a thorough investigation was done based on the data recorded in the flight data recorder (FDR), which was retrieved last Tuesday.

CAAN has already formed a six-member committee to probe the crash-landing, and a Bangladeshi delegation comprising CAAB officials has already gone there to provide assistance to the committee, if needed, CAAB Chairman Naim Hasan told The Independent.

The US-Bangla Flight-211 crash is the third biggest aviation disaster in Nepal’s history. Earlier, in 1992, within a span of a little over two months, Thai Airways Flight-311 and PIA Flight-268 crashed killing 113 and 167 people respectively, and entered into the record book as the second and third deadliest aviation disasters in Nepal’s history.

The Independent found from the records of the International Civil Aviation Organization (ICAO) that the investigation into the Flight-311 disaster had taken a little over one year and the investigation into Flight-268 had taken well over two years.

As the reasons behind the Thai Flight-311 crash, it is stated in the journal of International Flight Safety Foundation (IFSF) that the accident occurred because the pilot tried to approach the airport in a situation of lower than minimum visibility amidst heavy rain and could not maintain the course as set down in the approach chart. It also said the airport lighting system and approach chart did not facilitate the low visibility approach.

IFSF records of the Flight-268 crash suggests that the primary cause of the accident was that one or both pilots consistently failed to follow the approach procedure and inadvertently adopted a profile which was one altitude step ahead and below the correct procedure.

Why and how that happened could not be determined with certainty because there was no record of the crew’s conversation on the flight deck. Contributory causal factors were thought to be the inevitable complexity of the approach and the associated approach chart, said the IFSF about the largest aviation disaster that took place on Nepalese soil.

Canada-based Bangladeshi aerospace engineer Nakib Khan, who had worked in Bombardier—the maker of the Dash-8 Q400—told The Independent that investigating an aviation disaster is no small task. “Investigation will be conducted by several parties, including the aircraft-maker, civil aviation authorities of the country where the plane crashed, the insurance companies involved and, if needed, the International Civil Aviation Authority (ICAA),” he said.

About the possible method of investigation, Khan said the aircraft wreckage is normally re-assembled as much as possible. The pieces of physical evidence, even if initially hidden or distorted by the impact of hitting the ground or other factors, can start to suggest lines of inquiry, along with the “black box” and cockpit voice recorder, Khan added.

After the initial phase of gathering physical intelligence, it is normally possible to form a view of the physical process that brought the aircraft down—for example, an explosion, said the aviation engineer, who had graduated in aviation engineering from Toronto’s Ryerson University.

The results of autopsies performed on passengers and crew can also help narrow down what happened on board, he said, adding that the accident investigation process is very strictly a no-blame process. If investigators believe they have found a design or maintenance fault, they can issue recommendations immediately in order to try to prevent the problem affecting other aircraft, long before any final report is published, said Khan.