When should engines be overhauled? Some believe that the engine manufacturer’s recommendation are loose guidelines and that your mileage may vary greatly. Others adhere to them as gospel and treat them as mandatory. Times typically run between 1,500 and 2,500 hours and there’s usually a calendar factor of about 12 years so the guidance is for whatever comes first. Piston aircraft engines are extremely reliable when properly maintained, when flown regularly and correctly. You can see some important qualifiers creeping into the discussion. Some of the most outspoken advocates on both sides of the argument are extremely knowledgeable which means we best look deeper.
Several charity medical transport groups are beginning to require volunteer pilots to certify that their engines are below the manufacturer’s Time Between Overhaul (TBO) recommendations. There’s been some predictably negative reaction but the groups may have a point and here’s why. Under the FARs, flights for hire must have engines below TBO and while the charity flights are certainly not in that category, the groups are concerned that they kind of look like it to the FAA and NTSB. The groups are acting as a facilitator or broker between pilot and a trusting passengers, who likely know nothing about aviation safety. It’s quite a different relationship than when we just take a friend flying. Despite liability disclaimers and efforts to put a firewall between the group and the pilot, there’s a perception and an expectation of a higher level of care.
Reliable statistics are a great starting point for any safety discussion and in turbine aircraft, which are renowned for reliability, the manufacturer’s overhaul guidance is typically followed to the letter but there’s great emphasis on tracking. With piston engine aircraft, there just isn’t much to go on. For example, in the 2008 Nall Report there were 87 accidents attributed to powerplant malfunctions. What’s confounding is that we often don’t get the total time on the engine and prop.
We also don’t know how many parts and pieces are caught on the verge of failure and at what point in their life span. I know from personal experience that brand new engines are some of the quirkiest. It’s also true that organizations have no desire to be publicly called out, no matter how remote the risk, if there’s an appearance that they didn’t take every reasonable precaution to prevent a mishap.
We’d like to hear your thoughts pro and con.