rse and climb tempo of the stricken aircraft. Based on this emulation, it was ascertained that Shackleton 1718 was either at or very close to its intended cruise altitude of 2 896 m (9,500 ft) AMSL.
Instrument Flight Rules (IFR) flight had been authorised and the aircraft had been operating under IFR conditions at the time of its demise.
The Board was satisfied that the flight crew were under all circumstances both qualified and capable of performing the mission with which they had been tasked.
The accident occurred over State ground; property of the Department of Forestry. The terrain was unplanted, deforested and in its natural state. No claim could thus be made by the Department. There was no damage to private or other military property.
Shackleton 1718 was manufactured in August 1957. Although possessing a maximum take-off weight of 45 372 kg (100,000 lb), for its final flight it lifted off at 43 938 kg (96,840 lb). Since the aircraft was heavily laden with its maximum weight point close to the rearmost limit, the pilots would have experienced some instability in the yawing (left/right) plane.
The Board established that the impact speed of the aircraft was high and that this, combined with the resulting fire following the crash, caused almost complete destruction of the aircraft. There was no attempt by the crew to use parachutes and all aboard are assumed to have perished in the high G impact.
The Board established that the atrocious weather was a significant contributory factor in this accident. Wind was about 148 km/h (92 mph) due to the unstable air mass forming convection currents. Cloud cover extended from 305 m (1,000 ft) to 8 841 m (29,000 ft) AMSL with associated heavy precipitation. Due to the turbulence, the moist unstable air mass and low icing height resulted in unusually high icing conditions from 1 220 m to 1 829 m (4,000 ft-6,000 ft).
Air Force headquarters telephonically informed the Board that the maximum acceleration permitted on the Shackleton airframe was 2.4 G. It was thus theoretically possible to easily exceed this low limitation, especially under conditions of unusually high turbulence as in this case. Although it cannot be proved, it is not impossible that the pilot in control could have over controlled the aircraft on at least one occasion in response to the unusually heavy turbulence. This could have placed an additional load on the airframe.
It was considered a possibility that, due to the turbulence, the pilot found himself unwittingly between the mountain peaks and that either one wingtip or one of the tail surfaces skimmed the side of one of the mountains, the impact causing the aircraft to disintegrate in flight and causing the pilot to lose control. The Board, however, considered this scenario unlikely given the fact that the ATC heard the pilot's Mayday transmission clearly and the aircraft must have thus been flying above the mountain peaks under normal circumstances when the radio call was put out. Additionally, the fact that the dump valves were open does not correspond with a collision against a mountain.
The Board found Capt Silvertsen solely responsible for the accident. He displayed a complete lack of discipline by disobeying a direct order to rather route south over False Bay and instead routed over land, where the mountainous terrain exacerbated the already foul weather conditions. The aerodynamic effect of heavy icing, strong and turbulent winds, the heavy weight of the aircraft combined with the possible over control by the pilot in control, placed an unusually high loading on the airframe. This resulted in the airframe exceeding its design limits and initiated disintegration, leading to the loss of control and the consequent fatal crash. The accident was classed as an avoidable major flying accident.
All the evidence submitted by all the witnesses interviewed was considered credible by the Board.
Shackleton 1718 was delivered new to the SAAF valued at R 417 250.00. At the time of its demise it had completed 775.15 total airframe hours and, with depreciation, was valued w