The black box shows no sign of trouble before last month's accident on Lantau Black box recordings showed no sign of any equipment failure aboard a Government Flying Service helicopter before it crashed on Lantau last month, killing both airmen aboard. The preliminary report into the accident released yesterday also described how the aircraft smashed into the hillside, skidded, then plunged off the face of a steep slope before coming to rest. It confirmed that no emergency call was made by the airmen. The August 26 crash killed pilot Pang Fu-kwok, 34, and crewman Dickson Chan Man-tik, 31, when they were sent to pick up a patient on Cheung Chau at 10.29pm. A Civil Aviation Department spokesman said yesterday that the preliminary report must be regarded as tentative. 'More in-depth investigation and analysis work remains to be done before a conclusion can be drawn on what caused the accident. The final report is expected to be completed within one year,' he said. 'This preliminary report is published for general information.' The investigation is being conducted by the Civil Aviation Department with the participation of inspectors from the French Civil Aviation Accident Investigation Bureau. Britain's Air Accidents Investigation Branch also helped retrieve data from the flight data recorder, or black box, of the helicopter, a French-made Eurocopter 155 B1. The report said the helicopter had departed Chek Lap Kok airport at 10.29pm and then cut across Lantau via the Tung Chung Pass to pick up the patient on Cheung Chau. It said that three minutes after takeoff, while the helicopter was in level flight at an altitude of 375m, it hit the hillside on the western side of the pass. The combined cockpit voice and flight data recorder stopped recording at this point. The helicopter's fuselage then skidded 50 metres across the ground. The main rotor blades were severed within the first few metres as they smashed into trees and rocks, while the underbelly and right side of the fuselage suffered severe damage. As the slope dropped away, the remains of the helicopter shot off the edge and plunged 30 metres through the air before coming to rest. There was no fire. The report said the flight had been conducted under special visual flight rules, which require the pilot to remain clear of cloud and in visual contact with the ground. At the time of the accident the weather at the airport was within the Government Flying Service limits for single-pilot operations at night.