Mandatory vs. Required
Over the past couple of months (years), there has been a fairly large amount of controversy between the FAA and Part 91 operators concerning the requirements concerning the difference between mandatory and non-mandatory maintenance and inspections. To help put out the fire a bit, the FAA has issued (and bear with me for the boring numbers part) Notice 8900.410. This Notice is addressed primarily to Flight Standards District Offices (FSDOs) concerning what is "required," and what is "not required." And, although this Notice can trace its origins to a disagreement brought up by owners and operators of PT6A jet turbine engines, some of the content is applicable for piston powered owners and operators.
A big distinction made is the difference between what is considered "maintenance," and what is considered an "inspection." Overhauls are considered a maintenance action, NOT an inspection action (even though overhauls consists largely of tolerance inspections). Because of this, owners and operators under Part 91 can take comfort in the fact that they are only required to comply with a scheduled inspection program, allowing them to run their engine as far as they see fit past any published TBO. The FAA has issued AC20-105 (which they reference in Notice 8900.410) that documents some trend monitoring techniques to help operators determine when it's time to overhaul their engine, and GEMCO's Trend Monitoring sheets and philosophy are derived from the basic information provided in that circular.
Sadly, our Part 121 and Part 135 friends are out of luck, as the regulations require that they follow both an approved inspection, and maintenance program. This however, in our opinion, does not relieve them of trend monitoring. In fact, the regulations require certain 121 and 135 aircraft to have a trend monitoring program established and followed.
Where owners and operators can get themselves into trouble with this freedom is when they: 1.) do not take engine trend monitoring seriously; and when 2.) they stop addressing the financial and operational risks of operating in the "beyond TBO" range. Just because the FAA grants Part 91 operators the opportunity to operate past TBO doesn't necessarily make it the best choice. Too often, operating beyond TBO becomes a crutch people fall to when they have not appropriately prepared themselves for the liability of an overhaul. And, when this happens, trend monitoring usually goes by the wayside as the owner/operator is just biding all the time that they possibly can, trying to put off the inevitable.
So how can we responsibly take advantage of this operating freedom afforded to us by the FAA? Well, the first step is for owners and operators to have the mindset that the ability to operate beyond TBO is a privilege, not a right. We should never use it as a crutch, but rather a tool to help lower operational risk, and put some more cash in our pockets. GEMCO's overhaul program assumes that we don't get to access the holy land of "beyond TBO." Instead, GEMCO assumes that you'll overhaul your engine when it's supposed to be overhauled, and works to financially prepare you for that eventuality. If you do happen to have an engine that you can run past TBO, GEMCO lets you via our "fly on" program, which allows you to fly without paying any additional cash. The next step is to actively follow the advice conveyed in AC20-105, and use trend monitoring to our advantage. Engines rarely just quit. Instead, they slowly start to wear away, and eventually reach a failure point. By using trend monitoring, we can [almost] see inside the engine, and make intelligent decisions about what we should be doing. If we don't use trend monitoring, we have no data, and will be just be guessing as to what our next step should be.
So, let's be responsible owners and operators. Just because the FAA allows us to operate beyond TBO doesn't mean we can just blow through it without care. Instead, we all should look at operating past TBO as an additional responsibility, and a gift. When your engine reaches the geriatric stage of life, trend monitoring becomes more important than ever. Use it. Live by it. And, please, never use the extra time as a crutch to help you try and solve not accounting for the liabilities of owning and operating. The FAA recognizes that operating past TBO can be done safely when the appropriate precautions are taken. Take them, and you'll be able to experience all the benefits of operating in the "holy land."