Because engines are one of the biggest maintenance cost drivers on an aircraft, savvy buyers request engine pre-purchase inspections, notes JSSI’s Tony Rossi. Here’s an example why…
I had just snaked the borescope through the second and third stage LT stators and disks on the engines of the Citation V and was trying to get a peek at the HT Blades. “How does everything look in there?” The owner was anxious to hear if I had found anything. Standing nearby, the prospective buyer wasn’t saying anything - just waiting patiently for my report.
After a view through the borescope and pictures of the internal condition of the engine, I would get to the logbooks and spend some time looking at the Life Limited Component (LLC) history of these engines. There was a question about one of the impellers being timed out. A new impeller would be a high-dollar expense and add substantial cost to the upcoming engine overhauls.
This scenario played out many times during my tenure working for a Designated Overhaul Facility (DOF) for JT15D engines. Potential buyers would call us looking for an expert opinion and borescope report on the condition of the engine, commonly referred to as the engine ‘pre-purchase inspection’.
More often than not, the borescope inspection is just a precaution and a means to find any Foreign Object Damage or other damage in the engine not visible to the naked eye.
If you are in the market for an aircraft and are thinking about having a borescope inspection accomplished on the prospective aircraft, it’s always a good idea to start with a sales contact at the repair facility for that particular engine model or an FBO that is familiar with the airframe and engines. Most sales representatives will jump at the chance to provide this service because they can gather updated times and cycles from the engines’ log books, allowing them to track maintenance and provide quotes. Many times these inspections can be done at very reasonable rates.
One Pratt & Whitney Canada DOF sales person told me that in many instances they can provide a technician to borescope two engines at a cost in the $2,500.00 range. That’s a small price to pay for your peace of mind when purchasing an aircraft!
Warranty Coverage Issues
It is important to keep in mind that if a defect is found in an engine that is still under a manufacturer or overhaul shop warranty during a pre-purchase inspection, it’s possible that it won’t be covered! Why? Quite simply, there is no maintenance requirement for the borescope. The key here is that the engine was operating within normal parameters and the borescope was optional. That cracked PT or CT Vane you find would probably have been just fine until the next scheduled maintenance event.
You would be surprised at the amount of cracking on such a part that is actually within maintenance manual limits. Viewed through a borescope, damage typically looks worse than it actually is. Any findings during a borescope inspection called out in the maintenance manual (such as during a 400-hour nozzle flow on most PT6A series engines) are usually something that the manufacturer or overhaul shop will agree to consider and possibly warrant.
Realistic Cost Estimates
Many of the aircraft on the market today are 20-30 years old and the engine overhauls can cost as much as, or more than the value of the airframe. Knowing the Time Before Overhaul (TBO) or Hot Section Inspection (HSI) interval of the engines is critical as many owners sell an aircraft right at the time the overhauls are due.
If this is the case, talk to the overhaul shop and try to get a realistic estimate of the cost of the upcoming maintenance. Many providers will tell you there’s no way to predict the cost of an overhaul but they should be able to provide average costs. While there are always variables, it’s not as hard as you might think to get a very educated guess on these upcoming costs.
That brings us back to that borescope and log review on the Citation V mentioned at the beginning of this article. It didn’t initially make sense to me that only one impeller would be due on a pair of engines that were original to this aircraft. Those suspicions were confirmed; both were due. A discrepancy was tracked back to a flight hour and cycle reporting math error. These engines were in great shape and the aircraft was as well, but the owner and prospective buyer couldn’t come to a mutual agreement on how to value (or devalue) the aircraft, based on the upcoming overhaul costs.
A thorough understanding of the aircraft engines’ status is a key factor in the pre-buy inspection process and will provide insight to the overall cost of operating that aircraft for years to come.
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