New Delhi, June 4 -- Delhi airport's third runway, which has been shut since mid-February, may reopen only in September, several weeks after originally planned, as authorities work to shore up the tarmac's aircraft-handling capacity by 10%, said officials aware of the matter. The runway was shut for long-overdue strengthening and upgrades. It was due to reopen in early July, but this date has been pushed back as authorities put in place key systems to add at least eight flights an hour, parallel with the earlier work, to curb the possibility of another shutdown in the short term, said four officials aware of the developments. One of the officials said: "Considering safety and operational benefits, the proposal has already been agreed upon by all the stakeholders (AAI, DIAL, the DGCA and airline operators). The implementation plan along with the safety assessment report has been submitted to the regulator- DGCA (Directorate General of Civil Aviation) for approval." The extended closure will allow Delhi International Airport Limited (DIAL) and Airports Authority of India (AAI) to simultaneously undertake civil work, reduce the runway's displaced threshold - a section of the runway that aircraft are not allowed to land on - and replace a key navigation system. Officials estimate these changes could increase the capacity of the country's largest airport by about eight aircraft movements per hour. Officials said an extension of the Notice to Air Missions (NOTAM) declaring the runway unavailability is expected to be issued later this month. Another official said authorities decided to use the ongoing period of lower traffic to complete all the planned work at one go. "The date initially agreed was early July. However, some additional work needs to be completed. Since the number of flights being operated is lower because of schedule reductions announced by Indian carriers following the West Asia crisis, it has been decided to extend the closure rather than undertake another runway shutdown later," the official said. The Delhi airport, which can handle 84 air traffic movements (ATMs) an hour and nearly 1,500 ATMs a day, has been witnessing around a 5% reduction in flights, largely in domestic operations, since March. "Carrying out the threshold modification and ILS replacement simultaneously would avoid another lengthy runway closure in the future, since undertaking the works separately would have required fresh disruptions and relocation of the navigation equipment. Hence, DIAL and AAI also decided the works be done simultaneously," the official said....