History of Flight
On 15 August 2008 at 10:10Z, a Beechcraft F33A (registration ZS-RMA) departed Tzaneen Aerodrome (FATZ) in Limpopo Province to participate in an air race (Race of Champions). The aircraft was to fly a set course and return to Tzaneen. Approximately one hour and ten minutes into the race, while flying between Marble Hall and Vivo, the pilot experienced a sudden loss of engine power. The engine began spluttering and then failed. The pilot did not attempt to restart the engine but chose to land immediately. He spotted an open field on Appelfontein farm near Dendron and initiated a forced landing.
During the landing, the aircraft impacted a one-meter-high ridge at high speed, causing it to bounce. The pilot then lost control. The aircraft struck the ground at high speed and hit several thorn bushes before coming to a stop. The right wing and flaps sustained substantial damage; the propeller made contact with the ground. The nose landing gear and right main landing gear broke off upon impact. The aircraft came to rest approximately 55 meters from the initial impact point.
Injuries and Damage
Neither of the two occupants (pilot and navigator) sustained any injuries. The aircraft was substantially damaged. No other damage occurred.
Engine Examination
After recovery, the engine (Continental IO-520, serial number 822795-R) was examined. An attempted engine run produced a spluttering noise and was discontinued. The engine was removed for teardown inspection. Examination revealed that several teeth on the cam drive gear and its mating idler gear had failed. No other anomalies were found. The gears were sent for metallurgical analysis.
Metallurgical Findings
Metallurgical examination concluded that the cam drive gear failed in fatigue, causing four adjacent teeth to detach. These detached teeth caused further damage to both the cam drive and idler gears. The cam drive gear was made of suitable material, but the nitriding heat treatment failed to achieve the expected surface hardness, resulting in low tensile strength and reduced fatigue resistance. Additionally, the root radii on the cam drive gear were smaller than those on the idler gear, which would have contributed to higher stress concentrations. The engine failure was attributed to the failure of the camshaft drive and idler gears due to metal fatigue.
Probable Cause
Unsuccessful forced landing as a result of loss of engine power followed by an engine failure. Contributory factors included failure of the camshaft drive and idler gears, and metal fatigue.