The 40 indigenously-built advanced light helicopters (ALHs) the Indian Army has bought for Rs 1,747 crore (Rs 356 million) have a technical flaw that prevents them from flying to heights of 6,500 metres, thus affecting operational preparedness in high altitude areas like the Siachen glacier, India's audit watchdog says."The ALH was not able to fly above 5,000 metres, though the army's requirement stipulated an ability to fly upto 6,500 metres. This deficiency was because of the limitation of the engine used in ALHs," the Comptroller and Auditor General (CAG) said in his report released on Friday. The army needs choppers of the ALH category for quick movement of troops and logistics in operational areas, including in the extreme weather conditions of the Siachen Glacier. The helicopters are also meant to enhance surveillance capabilities. The Indian Army bought the ALHs despite other shortcomings like unacceptably high vibration levels. According to the report, the army ordered the ALHs after its manufacturer Hindustan Aeronautics Limited (HAL) said it would develop a more powerful engine to replace the existing power plant. "HAL, however, failed to overcome the shortcomings in the ALH even after five years as of December 2006. The inability to fly above 5,000 metres was due to the inability of HAL to reduce the empty weight of the helicopter as had been assured to the government," the CAG report said. "The army is compelled to rely on the old fleet of single engine Cheetah and Chetak helicopters which are of more than 30 years old technology," it added. "Failure of the army to acquire suitable ALHs timely has led to considerable dealy in de-induction of old fleet of Cheetah and Chetak helicopters, which may impact operational preparedeness of the army adversely, especially in high altitude areas in forward locations," the report maintained.