What happened
On 18 May 2009, a Cessna 210N, registration ZS-LTJ, was performing a ferry flight from a private airstrip near Moketsi to Tzaneen Aerodrome (FATZ) in the Limpopo Province. The flight followed an earlier leg from Rand Aerodrome where the pilot had encountered electrical low-voltage warnings. After taking off from Moketsi using an external battery pack to start the engine, the pilot proceeded to Tzaneen.
During the approach to runway 24, the pilot noted that the cockpit's landing gear indicator light appeared less bright than usual and observed an unusual noise coming from the electrical hydraulic pump. Although the pilot visually confirmed the gear appeared down and locked via an underwing mirror, the aircraft's electrical systems—including the radio and GPS—had been experiencing intermittent power.
Upon touchdown, the aircraft initially maintained its course. However, approximately 800 meters into the landing roll, the aircraft experienced a sudden instability in the tail section. The main landing gear struts subsequently collapsed, causing the aircraft to veer right and exit the runway, coming to rest on the grass clearway. The pilot was uninjured, though the aircraft sustained minor damage to the lower fuselage and the right-hand horizontal stabilizer.
The investigation
SACAA AIID investigators examined the aircraft's mechanical and electrical systems following the incident. Post-accident testing on jacks revealed that while the landing gear functioned normally when using a manual hand pump, the electrical system struggled under low power. Specifically, the battery could not provide sufficient voltage to the electrical hydraulic pump to generate enough pressure to fully lock the main gear in the down position.
Further inspection of the landing gear mechanism identified that the micro-switch on the left-hand main landing gear was misaligned. This misalignment caused the cockpit indicator light to show a "green" (down and locked) status even when the gear had not yet fully secured.
Findings
- The primary cause of the accident was an incorrectly adjusted landing gear micro-switch.
- A significant contributing factor was low battery voltage, which prevented the hydraulic pump from achieving the pressure necessary to lock the gear.
- The aircraft's flight logs were incomplete, as they failed to record previous electrical defects and voltage regulator replacements.
- The pilot did not perform the required pre-flight landing gear and horn function test as specified in the Pilot's Operating Handbook.