History of Flight
On 23 July 2010, at approximately 1000Z, a Cessna C188B aircraft, registration ZS-KDX, operated by Nelair Agricultural & Fire, departed on a local flight from Vivo, near Makhado. The pilot was the sole occupant. While in straight and level flight in close proximity to the airfield, a propeller blade separated from the propeller hub. The pilot responded by switching off the magnetos, stopping the engine. The engine sustained extensive damage due to severe vibrations caused by the imbalance after the blade separation. The pilot carried out a successful forced landing at the destination (Vivo) and escaped unharmed.
Aircraft and Pilot Information
The aircraft, a Cessna C188B (serial number 188-03068T), was manufactured in 1977 and had accumulated 7703.33 total airframe hours at the time of the incident. It was equipped with a Continental IO-520-D engine (serial number 572705) and a McCauley propeller (serial number 777355). The last mandatory periodic inspection was conducted on 30 October 2009, with 6716.0 hours since that inspection. The aircraft held a valid Certificate of Airworthiness issued on 7 July 2010, and was operated under Standard, Part 137.
The pilot, a 32-year-old male with a valid South African commercial pilot license, had a total of 261 flying hours, including 1.4 hours on type. His medical certificate was valid until 30 November 2010 with no restrictions.
Investigation Findings
Investigation revealed that the crack initiated on the outside of the blade root and progressed inward until final failure occurred. The separated blade was not recovered. Examination of the propeller hub showed beach marks indicating crack propagation. The propeller logbook indicated that the propeller had been correctly maintained according to records, and no propeller blade strikes were recorded. Various propeller maintenance organizations verbally stated that certain tasks required by the manufacturer's midlife inspection were not always performed due to cost implications, but none provided written confirmation. The weather, which was fine with light winds, visibility greater than 10 km, and no cloud cover, did not contribute to the incident. The aircraft was equipped with standard navigation and communication equipment, and no defects were reported prior to the flight.
Probable Cause
The incident's probable cause was determined to be a propeller blade separating from the propeller hub in flight.