NEW DELHI, June 26 -- The Indian Army's Cheetal helicopters continue to fly regular mountain sorties in the Ladakh sector, including the Siachen glacier, even as investigators examine a suspected technical failure that caused a recent crash, officials aware of the development said on Wednesday. The investigation has zeroed in on a material failure in the transmission system of the single-engine helicopter that crashed near Leh's Tangtse area on May 20, the officials said, asking not to be named. "The probe will identify which component in the transmission system failed after which corrective steps will be taken," said one of the officials. The Leh-based HQs 14 Corps, responsible for operations in the sector, operates around 25 Cheetals-a re-engined version of the workhorse Cheetah helicopter. "The heavier advanced light helicopter Dhruv cannot be used for front-line duties in the Ladakh mountains. The Cheetals, which have an exceptional power-to-weight ratio, have been flying daily since the May 20 crash," said another official. The two pilots-a lieutenant colonel and a major-and the third occupant Major General Sachin Mehta, General Officer Commanding of the Karu-based 3 Infantry Division, miraculously survived the crash with minor injuries, as first reported by HT. Equipped with a modern and fuel-efficient TM333-2M2 engine, the Cheetal features an automatic back-up engine control system. The Cheetal project began about 25 years ago to enhance high altitude operational capabilities, improve maintainability, and provide a mid-life upgrade for safe and reliable operations. The May 20 crash again highlighted the need for swift replacement of the ageing Cheetah and Chetak fleets - these helicopters were designed six decades ago. A string of crashes has led to scrutiny of the choppers' safety record. The army will begin phasing out the fleets in a year or two, and replace them with new light utility helicopters (LUHs) over the next eight to 10 years, as part of the Army Aviation Corps' drive to modernise its capabilities. The planned two-pronged replacement approach involves inducting locally produced LUHs and leasing similar choppers as a stopgap to meet critical requirements....