Engine failure has dire consequences. When you’re driving your car and you experience engine failure, you face being stranded on the side of the road and paying hundreds, if not thousands, for a tow and a solution. On the other hand, when you’re flying and you experience engine failure, you face the very real threat of falling out of the sky. With that in mind, it makes sense that aircraft engine overhauls are serious business.
An engine overhaul is a process of removing an engine, completely disassembling it, cleaning it, making repairs and replacements where necessary, and putting it all back together again for the sake of ensuring its airworthiness. An aircraft engine must always be properly functioning and airworthy, but due to its complex nature, the only way to make sure that all the parts are in proper working condition is to take it apart. A complete engine overhaul includes 10 steps:
1) receive the engine, 2) disassemble, 3) visual inspection, 4) cleaning, 5) structural inspection, 6) non-destructive testing, 7) dimensional inspection, 8) repair and replace 9) reassembly and 10) testing and reinstallation. The different inspection steps are of the utmost importance and therefore the most careful and precise; otherwise, everything is off, and airworthiness is dubious.
In order for the engine to remain airworthy, it has to meet FAA standards, which generally means that the aircraft operator has to follow the OEM outlined TBO schedule. TBO, or time between overhaul, is the engine’s OEM, or original equipment manufacturer, the recommended time frame between overhauls. Typically, the TBO is given as flight or operating hours. Countless tests have shown that deviating from the OEM recommended TBO dramatically increases the chances of an accident. And since nothing can be sure until either an overhaul or it’s already too late, following the recommendations of the OEM is your best bet.
In addition to the TBO, the OEM also typically includes specifications that need to be met for the overhaul and clearly defines what working condition is. Ultimately, how to approach the overhaul is up to the technician. But, when the technician signs the release form for the return to service of the overhauled engine, they are certifying that the entire overhaul process has been performed properly with the correct methods, techniques, and practices. The technician is saying that the best of their ability and knowledge, the engine has been overhauled correctly, so if that is not the case, the technician will be taking responsibility. Either way, overhauls shouldn’t be taken lightly.