Nepal Airlines Corporation (NAC) on Tuesday successfully conducted a test flight of its Chinese-made Y12e aircraft to Lukla Airport, five years after it was inducted into its fleet.

The carrier has also planned to conduct test flights to Simikot, Rara, Jumla and Dolpa airports on Wednesday.

“After the test flight, we will check the performance of the aircraft in line with the aircraft’s flight performance manual issued by the manufacturer,” said Captain D R Niraula, an expert at the Civil Aviation Authority of Nepal (Caan).

The NAC will provide details ranging from how many passengers the aircraft can carry at various temperature, wind, and altitude conditions and more on all the airports that it intends to fly to using the Y12e.

“The details provided by the NAC will be minutely assessed and calculated before allowing it to begin commercial operation,” he said, adding that it would take a few days to produce the detailed reports on the aircraft’s performance.

The 17-seater Y12e arrived in Kathmandu in 2014 and was intended to serve remote mountain airfields like Lukla, Jomsom, Manang, Simikot, Rara, Jumla and Dolpa.

But the plane had a regulatory limit, meaning that it could only fly to airports with a maximum grade of up to 2 percent or about 1.2 degrees of slope. The regulator Caan had to clear the aircraft to serve airports with a slope of more than 2 degrees.

As a result, the Y12e was only operated on the Pokhara and Simara sectors, pending the issuance of commercial flight clearance by Caan on mountain airfields. Pilot shortage had also prevented the NAC to conduct the test flight of Y12e at the Lukla Airport although it was approved on November 23, 2016.

The runway at Lukla’s Tenzing-Hillary Airport has an 11-degree slope. Most of the short take-off and landing (STOL) airfields in Nepal including Lukla in Khumbu are above the regulatory limit.

Although the Harbin Yunshuji Y-12-II had made thousands of flights all over Nepal and has been described as the best aircraft to serve short take off and landing (STOL) airfields, the new regulations by Caan to ensure safety had prevented the new version Y12e from flying to mountain airstrips. The NAC has four Y12e aircraft on its fleet.

According to the performance analysis report of the Y12e aircraft submitted by the NAC to the Tourism Ministry in 2015, the Y12e flies well in very cold weather, with performance falling with a rise in temperature and altitude. However, the plane performance improves if the runway is long.

For example, the Y12e can fly from Kathmandu to the STOL airfield Khanidanda at full capacity when the temperature is 0 degrees Celsius. At 14 degrees Celsius, the plane can carry only 12 passengers; and at 30 degrees Celsius, the allowable cabin load drops to a mere six passengers.

Likewise, the performance report showed that on the Nepalgunj-Jumla sector, the aircraft can fly at its optimum capacity when the temperature is 0 degrees Celsius, and when the temperature rises to 18 degrees and 30 degrees, the cabin load decreases to 14 and 7 passengers respectively.

The Y12e is totally unsuitable for the Pokhara-Manang sector, according to the report. The allowable cabin load is seven passengers at 0 degrees, two passengers at 10 degrees and zero passengers at 14 degrees Celsius.

The aircraft can fly with 12 passengers in all weather conditions from Biratnagar to Taplejung. Likewise, on the Jomsom-Pokhara route, it can fly with 16 passengers in all weather conditions; but on the return flight, the passenger load has to be reduced to 14, the report showed.  

From Lukla to Kathmandu, the Y12e can carry 16 passengers in all weather conditions; but from Kathmandu to Lukla, the number has to be reduced to 13. The report has mentioned that the cargo load has to be slashed significantly as well.