What happened
On September 23, 2008, a privately operated Cirrus SR22 was conducting a flight from Fontenay Tresigny to Le Havre Octeville. During the cruise phase, approximately 8 nautical miles southwest of Toussus-le-Noble, the pilot noticed that the oil pressure was slightly higher than normal. Shortly thereafter, a significant amount of oil was sprayed onto the aircraft's windshield, severely obstructing the pilot's view.
Due to the reduced visibility, the pilot decided to divert to Toussus-le-Noble. After informing air traffic control of the situation, the pilot commenced an approach to runway 07L. To navigate the approach, the pilot relied on the Multi-Function Display (MFD) and performed a short slip on final approach to regain visual contact with the runway. The aircraft landed safely with no injuries or damage reported.
The investigation
The investigation focused on the cause of the oil pressure increase and the subsequent spray. It was discovered that earlier in 2008, the pilot had installed a non-manufacturer-approved modification: a two-part closure system on the engine's oil system breather. This system was intended to prevent oil from leaking while the aircraft was parked in a hangar. The modification consisted of a fixed component and a movable part that could be opened or closed with a quarter-turn.
While the pilot had recently decided to leave the system in the open position, a trainee mechanic had inadvertently closed the mechanism during the aircraft's annual maintenance cleaning the day before the flight. This change in the system's state was not detected during the three subsequent pre-flight inspections.
Findings
- The primary cause of the incident was the failure to verify the status of a non-standard modification prior to flight.
- The closure of the engine breather caused an internal overpressure within the oil system.
- This pressure buildup led to oil being forced out through the crankshaft oil seal, resulting in the spray on the windshield.
- The modification itself was an unauthorized addition not approved by the aircraft manufacturer.