Over the last 40-some years, I have been involved in numerous conversations with aircraft owners, pilots, mechanics, manufacturer’s representatives, and FAA personnel, to name a few, regarding the two different engine inspection programs: Hard-Time and On-Condition. My early conversations consisted of understanding the differences between the maintenance philosophies and trying to decide which one is better.
After all of these years, the discussions are very similar, and there never seems to be a clear-cut answer as to which program is better. This is an important maintenance decision with serious cost implications. So let’s take a closer look at the options, starting with a simple explanation of each inspection program.
Any engine under this type of inspection program typically requires two disassembly events. The first is the Hot Section Inspection/Mid-Point Inspection that is completed at a specific hourly interval (usually at half of the overhaul limit).
The second disassembly event required for Hard-Time engines is referred to as the Overhaul, which is also performed at a specific hourly interval. Discrepancies must be corrected; tolerances fully restored to almost-new condition, and Life Limited Components (LLCs) replaced. The original philosophy behind Hard-Time came about in the early days of the aircraft industry with reciprocating engines and before more complex commercial turbine engines were developed and put into service.
The On-Condition engine does not require a Hot Section Inspection/Mid-Point Inspection or require an Overhaul for the engine to continue in operation. The engine program requires disassembly of the engine only when there are discrepancies discovered through routine inspections and checks that need correction, or when LLCs reach maximum life and need replacement, just like Hard-Time maintenance. The engine might require extensive work, similar to an overhaul, or minor repairs, depending on how much wear is found at the time of disassembly.
Not all corporate turbine engines have the option for On-Condition inspection programs; those that don’t must be maintained in accordance with the Hard-Time inspections. The Manufacturer’s Maintenance Manual for the airframe — engine, or both — can stipulate which inspection program is required. So it is important to research your specific aircraft as to which program options are available.
The optimal engine inspection program for your operation should be determined prior to purchasing an aircraft. This will prevent selecting an aircraft that does not have the preferred type of program available. The program decision should be based on the estimated annual hourly and cyclic usage, the expected number of years of ownership and the general mission for the new aircraft.
I recommend that the owner and operator sit down with an experienced engine maintenance technician that can provide input and guidance to help them make an informed decision. This decision will affect the maintenance for the entire life cycle of the engines and it should be made by using all of the information that is available.
At the point of delivery of a new aircraft, if both options are available, select the preferred choice and incorporate the program’s requirements with all of the data into a pre-selected Maintenance Tracking System.
When purchasing a pre-owned aircraft, I suggest that the tracking system be reviewed thoroughly to assure that the correct program and all its requirements are listed in the system. Over the years, I have found maintenance items in tracking systems that were required for a Hard-Time program but the engine was On-Condition, resulting in maintenance items being performed, sometimes with significant expense, despite the fact they were not required.
Switching from One to the Other
There are ways to change inspection programs for a pre-owned aircraft engine from Hard-Time to On-Condition or On-Condition to Hard-Time, but this can be a difficult and expensive decision. You will need to contact the engine manufacturer for your specific model of engine and the FAA (or other applicable aviation authority) to obtain a full understanding of the procedures and related costs.
The option of operating an engine under Hard-Time that is currently under On-Condition is always possible by just doing the maintenance required for Hard-Time, including the Mid-Point Inspection and Overhaul. Then continue to perform any special On-Condition requirements and leave the inspection program identified as On-Condition. Remember, the inspection program is the minimum work required for airworthiness, and performing the maintenance for Hard-Time and On-Condition programs, exceeds the minimum maintenance required for either program. Doing this allows future owners to have the option of a Hard-Time or On-Condition inspection program when it comes time to sell the aircraft.
The answer as to which inspection program is best for your aircraft engines may not have been provided in this article, because much of the decision comes down to specific aircraft profiles and individual preferences and philosophies about maintaining an aircraft. The way I look at it is: why make it a mandatory airworthiness issue with an inspection program that requires expensive Mid-Point and Overhaul inspections, when the option is always available with an On-Condition inspection program? Of course, many times On-Condition is not an option, especially with smaller engine types.
My real point is that this is an important maintenance decision, and it’s not a simple one to make. Do your research, contact an engine maintenance expert and take everything into consideration before selecting a Hard-Time or On-Condition inspection program for your engines.