On Dec. 16, 2025, the FAA issued an Airworthiness Concern Sheet (ACS) for Lycoming IO-360 engines and AVStar-manufactured vertical- and horizontal-mounted fuel servos. According to the ACS, operators and original equipment manufacturers have reported instances of uncommanded engine shutdowns on aircraft equipped with Lycoming IO-360 engines and AVStar-manufactured vertical- and horizontal-mounted fuel servos when the throttle was reduced to idle, referred to as “rollbacks” or “rollback events.”
The ACS states that “These events have been reported on production and in-service Cessna 172S and 172R as well as the Piper Archer III, Pilot 100i, and Seminole aircraft having IO-360 engines. The FAA is asking operators and maintainers of aircraft with IO-360 engines for information if they have experienced similar issues on their aircraft, regardless of fuel servo manufacturer or installation orientation.”
An ACS serves to inform the fleet of potential safety issues and to gather data to help identify corrective actions. Any response or action to it is greatly appreciated and completely voluntary.
If a rollback event has occurred, operators are asked to report the configuration of the aircraft, including the model and serial number of the aircraft, total flight hours and cycles on the aircraft and engine since new or overhaul, as well as monthly usage rate. Additional details of any reports should include the fuel servo manufacturer, part number, serial number, time since new, cycles since new, time since overhaul, cycles since overhaul, and installation orientation (horizontal or vertical).
The ACS specifies additional information that is also requested after such an event.
Contact David Bergeron, Engine & Propulsion Aviation Safety Engineer at the FAA’s Eastern Certification Branch via email at ECB-COS@faa.gov or 860-386-1805.
Injection servos, like diaphragm-driven fuel pumps, rely on the sensitivity of flexible diaphragms that both pump and regulate fuel flows. Field experience has indicated some hardening of these rubberized metering devices resulting in operational anomalies. When these diaphragms and check valves become stiff and inflexible, range-resolution, as well as response times, are compromised. In extreme cases, roll backs, as described, will occur.
It is important to get comments from the field in this effort. TIS and calendar age noted for affected engines is vital to determining root causes.
Good article! Short and to the point and easy to read. Thanx!