Confirming reports from Kiev that a $400-million deal has been signed to upgrade close to 100 of the twin-engine aircraft operated by India, Ministry officials said that a “life extension” contract was inked “recently”.

While Ukraine had won the tender to upgrade the transport aircraft in February, reports said that the formal contract was inked on Monday, four days after the June 9 crash. The IAF had began the process of upgrading the AN 32 aircraft in 2001 as it was nearing the end of its service life. The AN 32 aircraft, inducted in 1984, are the backbone of the IAF’s transport fleet.

The upgrade announcement comes even as investigators are struggling to recover the flight data recorder, or black box, of the aircraft that crashed shortly after taking off from the Mechuka landing base, close to the Chinese border.

A senior officer said that bad weather conditions — it has been raining incessantly in the area — have been holding up search operations and ground teams are yet to locate the vital black box needed to establish the cause of the crash.

“Photographs of the black box have been distributed to search teams to help them identify the equipment. Army personnel and members of the Air Force mountaineering team are assisting in the search,” a senior official said.

The black box is especially critical to determine the cause of the crash as the aircraft did not send out any distress messages or signals before slamming into the mountains of Arunachal. One of the few clues investigators have is eyewitness accounts by villagers that they saw the aircraft on fire before it went down.

Defence Ministry officials said that the upgrade deal has been signed with the Foreign Trade Enterprise of Ukraine and the life-extension program will start this year itself. While the first batch of aircraft will be sent to Ukraine between 2009 and 2013 for refurbishment, the remaining aircraft will be upgraded at the Kanpur-based Base Repair Depot of the Air Force.

The upgrade will include life-extension programs for the engines, new avionics and installation of modern communication equipment. The IAF hopes to extend the life of the aircraft by close to 15 years while the refurbished engines will also improve the range and cargo-carrying capacity of the aircraft.