What happened
On January 20, 2008, a Cessna 177B, registration I-LFSA, crashed in a field near Costano, in the municipality of Bastia Umbra, Italy. The aircraft was conducting an advanced instrument flight training mission for a commercial pilot license candidate, accompanied by a flight instructor. The flight originated from Rome Urbe airport with the intention of landing at Perugia S. Egidio airport.
During the approach to Perugia, the crew was stabilized on the ILS approach and had been cleared for a missed approach. Approximately two minutes and 44 seconds after receiving this instruction, the aircraft impacted the ground in a plowed field, roughly 4,540 meters short of the runway. Both occupants, the instructor and the student pilot, sustained fatal injuries upon impact. The aircraft was destroyed, though no damage was caused to third parties on the ground.
The investigation
The ANSV investigation examined the aircraft's maintenance records, the flight's technical history, and the environmental conditions at the time of the accident. Investigators analyzed the wreckage and found no evidence of structural failure or engine malfunction, noting that the engine was operating at high RPM at the moment of impact.
Technical scrutiny focused on the aircraft's vacuum system, which powers the gyroscopic instruments. The investigation revealed significant discrepancies in maintenance documentation. Specifically, the primary vacuum filter had exceeded its calendar life limit and had not been replaced according to the manufacturer's annual requirement. Furthermore, investigators found that a filter of an incorrect type had been installed, and there was no documented evidence of the part's origin or proper certification. The investigation also noted that the aircraft's radio station license had expired two years prior to the accident.
Findings
- The primary cause of the accident was a loss of control in flight induced by the unreliability of the artificial horizon.
- The instrument failure was likely caused by a clogged vacuum system filter. High humidity and ambient temperatures at the dew point likely caused moisture to condense on the expired filter, leading to a rapid blockage of airflow.
- The low altitude and limited visibility during the approach left the crew with insufficient time to regain situational awareness and recover the aircraft.
- Maintenance quality was compromised by the use of incorrect components and failure to adhere to mandatory replacement intervals for the vacuum system filters.
- Meteorological conditions at the time of the accident included significantly reduced visibility, as indicated by a SPECI report showing horizontal visibility of only 300 meters.