TIA’s ageing runway ‘cannot handle big jets’

KATHMANDU, APR 18 -

The runway at Kathmandu’s Tribhuvan International Airport ( TIA ) is not strong enough to handle wide-body aircraft due to its ageing asphalt foundation, and distress is caused to the upper surface instantly when heavy jets land, said a study report.

An investigation conducted by Ayesa Ingenieria of Spain said that damage in the lower asphalt layers is reflected quickly in the upper surface resulting in cracks and other damage.

Repeated occurrences of cracks on the runway at the country’s sole international aerial gateway have been affecting smooth operation of aircraft since 2011. Scores of flights have been diverted or delayed in recent years due to problems in the 3,050-m runway.

Trouble mainly occurs during the rainy season. The report said that lack or malfunction of subsurface drainage was another reason behind the damage in the lower asphalt. The Civil Aviation Authority of Nepal (Caan) had assigned the Spanish company to conduct a study of the runway last year following repeated occurrences of the runway coming apart. A preliminary study report was submitted to Caan recently. The full report is due to be presented next week.  

The study report has suggested that the lower layers of the runway be dug up and the foundation repaved by removing damaged asphalt layers and substituting them with a new base and surface courses. It said that the old surface courses working as the base course had less stiffness than required. However, due to the thickness of the runway, it has not seriously obstructed aircraft operation. The report said that when compared to the core part of the runway between 2006 and 2013, damage to the intermediate layers was due to operation of large jets like the Airbus A330 and the Boeing 777.

“The runway was designed for DC 10 aircraft, and now wide-body aircraft like the Boeing 777 operate on the runway which have double the capacity of the DC 10,” said Narayan Singh, deputy team leader of Caan’s Air Transport Capacity Enhancement Project.  

In 2013, there were 1,000 operations of A330-300 aircraft, 955 of Boeing 777 and 452 of A330-200, and the numbers are expected to double in the next 20 years.

“The lower level of the runway built with conventional asphalt foundation is unable to handle the stress of heavy aircraft. Operation of bigger aircraft is increasing, and it is causing deterioration to the runway and taxiway pavement.”

Cracks first appeared on the runway in June 2011, and they have become a recurrent problem now. Cracks were reported occasionally in 2012. However, the problem worsened last year, forcing Caan to take a harsh decision to bar wide-body aircraft from landing at TIA for a month.

To prevent further damage to the runway, Caan in August last year requested international carriers serving Kathmandu to use smaller aircraft or restrict their load to 196 tonnes.  

The report has suggested applying Kjellbase, which is a discontinuous graded asphalt mix with fibres. Kjellbase is normally used at international airports that need a deep pavement reconstruction.

“The removal of weak layers will help TIA to handle any type of aircraft pressure until 20 years,” said Singh. The report said that international operations were expected to double in the next 20 years, and that there would be an increase in the operation of bigger and more efficient aircraft. Based on the growth pattern, removal of weak layers will help TIA to keep its runway in good condition for the next 20 years.

Meanwhile, Caan has started the process of reconstructing the runway pavement and taxiway. As per the plan, 20 m of the 45 m width of the runway blanketed with damaged asphalt layers will be removed.

The report has estimated a bill of US$ 28 million for the project. The total construction time of the project is 19 months which includes tendering, awarding the contract and construction work. However, the net construction time which is 6 hours in the night time for runway construction is 4 months. For taxiway construction, the report said that at least 8 months would be required.  

The runway was extended to 2,000 m by USAID in 1967 and again to 3,050 m in 1975. Overlay work on 2,000 m of the runway was done in 1985 and on the entire runway in 1995. Resurfacing of the runway and taxiway was completed by Caan in 2011.

Source: The Kathmandu Post