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Rehab for bumpy runway

Calcutta airport’s worn-out main runway is set to be relaid alongside the heavily cratered highway that runs along its boundary.

The runway in its present state is a bumpy ride for aircraft after years of patchwork, a sham annual ritual that Calcutta’s battered roads are familiar with.

A study by the Central Road Research Institute (CRRI) a few months ago revealed damage to various portions of the runway. The study report recommended resurfacing the runway and laying a sheet of synthetic fabric under the bituminous layers to prevent rainwater from accumulating.

“Work will start by the end of the year and we are planning to complete relaying the runway before next monsoon,” airport director B.P. Sharma told Metro.

The project will be scheduled in such a manner that flight operations won’t be affected. A temporary ramp will be built over each peeled-off portion so that flights can use that stretch when work isn’t underway.

“Work will be done mainly at night. When the main runway is closed, the secondary runway will be in use. So there won’t be any disruption,” Sharma said.

Pilots landing or taking off routinely complain about the undulating surface of the main runway.

“The ride here is a rough one whether you are landing or taking off, unlike in airports such as Delhi or Bangkok. Patchwork is the main culprit,” said Capt. Sarvesh Gupta, a veteran pilot and chairman of the Airlines Operators’ Committee at Calcutta airport.

Most domestic airlines, including IndiGo, Jet Airways, and SpiceJet, operate narrow-bodied Boeing 737 and Airbus 319 and 320 aircraft that weigh 60 to 65 tonnes and land at speeds of around 250kmph. International airlines operate wide-bodied aircraft— Airbus 330 and 340 and Boeing 777 and 747 — that weigh about 350 tonnes each with landing speeds of around 250kmph.

A loaded six-wheeler truck weighs about 20 tonnes, which means the runway takes the impact of 18 six-wheeler trucks when a Boeing 747 lands.

“The impact caused by wide-bodied aircraft such as the Boeing 747 with a full load of passengers and cargo is huge. A runway also has to take the pressure of aircraft moving at high speed while taking off or after landing, which is why the surface has more layers of concrete, gravel and bitumen compared to a road,” said a scientist.

The two runways handle about 250 flights every day, far fewer than Delhi’s average of 900 but with a surface several times more vulnerable to damage. Officials said that the main runway had undergone frequent patchwork over the past couple of years because craters were showing up at regular intervals.

“Since resurfacing is long overdue, there is natural wear and tear,” an official said.

Two other factors make the main runway prone to damage. The study revealed that during monsoon groundwater rises till one metre below the runway, eating into the bituminous layers.

The runway also suffers because of multiple weather changes — hot and humid summer days, heavy rain during monsoon and single-digit temperatures in winter.

“Both runways suffer more wear and tear because of heavy rainfall. Rain is the biggest enemy of bitumen,” the official said.

Parts of the runway also become slippery because of rubber deposits from aircraft tyres. According to the study, rubber deposits need to be scraped off to meet the safety requirements of a runway.

The last time that the 3,627-metre stretch of the main runway underwent an overhaul was in 2003-04. “Resurfacing has been due since 2011,” an expert said.

The CRRI has recommended a special drainage technique to reduce damage to the main runway from rainwater. “Drains will be dug on both sides of the runway. The synthetic fabric sheet will drain the water out into these drains, which in turn will carry the water to the main drainage system 60 to 70 metres from the runway,” Sharma said.

The airport’s main runway has a base of concrete, which a CRRI scientist said was probably laid during British rule. The concrete base is covered with granular sub-bases, gravel and several layers of bitumen.

Sources said the runway’s thickness was variable across five sections, the thickest layer being on the stretch along the centreline where aircraft movement is the maximum.