CASA this week released an Airworthiness Bulletin reminding engineers about the monitoring requirements for on-condition maintenance.
AWB 02-001 dated 23 July was issued in response to an ATSB investigation into a fire and fatal crash involving a Mooney M20 near Luskintyre, NSW, in 2022.
The AWB states that some engineers appear to have forgotten that "on condition" requires active monitoring such as repetitive inspections or tests to ensure the component or system remains functional.
"Some operators and maintainers, including some Licensed Aircraft Maintenance Engineers (LAMEs) have come to believe that 'on condition' means fit and forget," the AWB points out. "They believe that it’s OK to not do anything until a failure occurs.
"Maintenance practices that mistakenly equate 'on condition' to mean 'fit-and-forget' and/or 'fit-until-failure' will not achieve the levels of safety and reliability that are inherent in the design of the aircraft.
"At best, this may cause operational surprises, which could prove very costly. At worst, this may jeopardise the safety of an aircraft and its occupants."
On-condition maintenance refers to the inspections and checks used to detect degradation in condition or performance. Items are left in service on the condition that they continue to meet a desired physical condition and performance standard.
Most commonly, engines of aircraft in the private and air work categories can be run on condition, which enables the aircraft owner to bypass the TBO time provided an engineer is satisfied with the engine. An engine needs to be re-inspected and signed-off again at the next periodical check.
"The item's performance may relate to, but are not limited to, cleanliness, cracks, deformation, corrosion, wear, pressure or temperature limits, leaks, loose or missing fasteners, and are published in the approved data of the aircraft or aircraft component," the AWB states.
"Therefore on condition maintenance means an inspection / check that may result in the removal of an item before it fails in service."
Mooney VH-UDQ crashed in 2022 after an O-ring on the engine-driven fuel pump failed due to deterioration, causing a fire in the engine compartment. Although the pilot attempted an emergency landing, the aircraft struck trees short of the airport. The pilot later died in hospital.