What happened
On October 13, 2013, a Zlín Z 43, registration OK-DOI, was performing a landing pattern at Šumperk airport when the pilot experienced a sudden engine failure. The aircraft, operated by AK Šumperk, was being flown solo by a 55-year-old pilot.
Approximately nine minutes into the flight, the engine ceased functioning. Due to the aircraft's position relative to surrounding terrain and obstacles, the pilot executed an emergency landing in a field near road number 11 in the direction of Rapotín. The field surface consisted of soft, clay-like soil following recent subgrade work. Despite the engine failure, the aircraft sustained no damage during the landing, and the pilot remained uninjured.
The investigation
The ÚZPLN investigation focused on the mechanical failure of the M337A engine. A technical inspection of the engine conducted at Šumperk airport revealed that the drive for the LUN fuel pump had disconnected from the camshaft.
Investigators found that the fuel pump drive is connected to the camshaft via a carrier secured by a pin (p/n SC3219). This pin had fallen out of the carrier and was found at the bottom of the camshaft housing. The displacement of the pin caused secondary damage, including a rupture in the intake pipe (p/n SC3327) and damage to the oil cleaner plug (p/n SC0386) within the distribution housing.
Findings
- The sudden engine failure was caused by the disconnection of the LUN fuel pump drive from the camshaft.
- The disconnection occurred because the connecting pin (p/n SC3219) fell out of the carrier.
- The investigation determined that the pin had not been properly secured during a major overhaul (GO) performed in 2003. The dimpling process used to secure the pin was incorrectly executed, failing to sufficiently displace the material to prevent the pin from migrating out of the hole.
- The pilot was qualified and the aircraft was airworthy, with all maintenance and operations in compliance with regulations.
Safety action
- The ÚZPLN issued a safety recommendation for LOM Praha to assess and revise the technological procedure for securing the SC3219 connecting pin during overhauls and repairs of M337 series engines.