Points for Pilots

The Rotax 912 engine and the related 912S and 914 engines have many parts made of rubber or closely related material. To guard against failure of these parts, Rotax recommends replacement based on hours in service and elapsed calendar time. If that replacement policy is to work for all possible installations, in particular in very hot Africa and very cold Alaska, then the replacement intervals must be quite small. As the US Air Force discovered many decades ago, such frequent replacement triggers so many new problems that the cure becomes worse than the effects of the aging process. Since that discovery, the Air Force has used on-condition replacement, where parts are replaced as needed and not due to some time-in-service or calendar-time rule. The conclusions drawn by the Air Force apply to the Rotax engines as well. My friend Philip tells horror stories about the difficulties created when wholesale replacement of all rubber parts is done every few years on his Rotax 912S, as ma