Critical runway maintenance and repair work that has been under way at Mumbai airport since February 7 is set to end this Saturday, allowing for smoother landings and takeoffs, along with the restoration of 230 cancelled flights.

The nearly ₹100-crore project work involved recarpetting the critical 50,000 sq. mt. intersection of the two runways with bitumin. The last time such an elaborate exercise was carried out was in 2009-10. “A resurfaced runway depending on factors like jet blast, weathering action, rubber deposits etc will last 7 to 8 years,” officials of Mumbai International Airport Ltd. (MIAL) said during a media tour of the runway intersection area. Similarly, MIAL had earlier carried out preservation of the runway surface by applying airport-grade sealguard technology from the US in 2016.

Officials of MIAL and Asphault India Corporation, which is carrying out the resurfacing works explained that the integrity of runway surfaces is assured by regular inspections. A team of 600 workers work as per a well planned exercise to ensure that the work in hand is completed within the available 6 hour window period between 11 a.m. and 5 p.m.

“Pavement maintenance requires periodic renewal of the top or wearing surface. The most commonly used hard surface types are concrete and asphalt. In Mumbai, we use bitumen or asphalt,” the MIAL official said.

Mumbai, being the busiest single-runway airport in the world, has close to 1,000 movements (both aircraft takeoffs and landings) in a day, making airport closure a serious matter. “About 260 flights had to be cancelled, affecting close to 50,000 passengers,” officials said.

To ensure that the quality of raw material is maintained, a bitumen plant was installed within the airport premises. “Special permission was granted for this plant because if we had to source the asphalt from outside then there could be problem, since it would be located 40 km away. For laying the runway surface, maintaining temperature management is critical,” the official said.

To ensure this, the plant had to be fired at 4 a.m. every Tuesday, Thursday and Saturday. When work would begin, a little after 11 a.m., asphalt produced at 200 degrees centigrade would be brought to the site in 100-odd trucks and laid at 170 to 150 degrees centigrade. “Finally, it had to be rolled before 100 degrees centigrade so as to ensure that it did not become hard as it will then not meet quality parameters,” an official explained.

Besides recarpeting, MIAL has also completely redone the Aeronautical Ground Lighting System at the intersection. Work carried out by AMA India saw 275 runway lights being removed and replaced. MIAL was the first airport to commission a comprehensive photometric test of the Airfield Lighting System at the airport. AMA had entered into contract with MIAL for carrying out repeat tests twice more in 2017-18.

Regular maintenance

To ensure that the runway intersection is in good shape, MIAL conducts 40 minutes of critical maintenance daily. “A thorough check of the intersection is conducted between 3.20 a.m. and 4 a.m. every day. There are no flight movements at this time. Besides this, a 11-minute window is available for maintenance every Monday afternoon,” officials said. Though operations are suspended for 15 minutes between 1.45 p.m. and 2 p.m. on Monday, four minutes go in maintenance staff reaching the intersection and withdrawing. Apart from the runway intersection area, the rest of the two runway surface areas are maintained for four hours a week: two hours each on Monday and Thursday.

Bump index

During the past year, MIAL also conducted a bump study of the runway surface, the first by any Indian airport. Called the Boeing Bump Index, the study, carried out by a Denmark-based company, helped MIAL evaluate runway roughness, which can increase stress on airplane components, reduce braking action, make it difficult for pilots to read cockpit instrumentation, or cause discomfort to passengers. “This study did throw up some rough surface spots along the runway and we are working on it,” the official said.

Culprit airplane

It is not the huge four-engine double-decker aircraft like the Airbus 380 or the Boeing 747, but the Boeing 777-300 ER, operated by airlines like Air India, Jet Airways, Emirates and Singapore Airlines to Mumbai that causes the most damage to runway surface. “This is due to its wheel configuration. It has a narrow wheel base and thus puts more pressure on the runway surface. The Airbus 380 puts far less strain on the runway,” officials said. They said that from 3 to 4 kg of rubber being deposited during landing by narrow-body aircraft, 8 to 10 kg is deposited by wide bodies, while 15 to 18 kg of rubber is deposited by super jumbos like the Airbus 380.