THE only helicopter rental company in Hong Kong has been forced to tighten its maintenance procedures in order to keep its operating licence following a crash initially attributed to an error by an engineer. Sek Kong-based Heliservices has also advised the French manufacturer of the Lama aircraft to change the colour of vital safety components to help avoid a repeat of the June 29 accident. An interim report by the Civil Aviation Department attributed the crash to the failure by an engineer to replace vital safety devices during routine maintenance. During the flight, a tail rotor worked loose, the pilot lost control and the aircraft made three rotations before making a crash landing. The 31-year-old pilot was only slightly injured. Following the accident near Yuen Long, the company was banned from using Lamas with under-slung loads, but the ban was later lifted. However, sources said the lifting of the ban was dependent upon the company tightening its maintenance procedures. The crash, which wrecked the aircraft, followed a similar incident on June 9 when another of the company's Lamas crashed in the same area. An Aviation Department interim report said the pilot was trying to land in an area smaller than half the size of that laid down in the company policy handbook. It is understood the cause of that accident was 'ground resonance' which can make the aircraft uncontrollable. The company had replaced one Lama with a leased aircraft from the United States, sources said. It is also about to submit for testing with the Aviation Department a Lama which crashed in 1992, killing the pilot Russell Nairn. The helicopter has been rebuilt following the crash, which occurred during work in the Castle Peak ranges, and will soon undergo an airworthiness test. Meanwhile, the report into the China Airlines Boeing 747-400 which crashed into Victoria Harbour in November 1993 was completed at the weekend, and awaits publication.