By Pratt & Whitney Certified Line Maintenance Repairman Steve Wightman
- Brief history
- Experience in industry and personal experience.
- Preventive maintenance, PM, has many benefits.
Experimental PM Program for N71RJ
Since its introduction in 1964, largely to the U.S. military, the PT6 series has flown hundreds of millions of hours with – relative to piston engines – very few faults. The PT6 is truly a marvel of engineering.
There are 4 options pertaining to Time Between Overhauls (TBO).
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Standard TBO as issued by the engine manufacturer.
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Request an extension from Pratt & Whitney, PWC.
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Develop an FAA-approved maintenance program. (N71RJ’s choice).
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Use FAA type certificate, STC, to lengthen TBO, I.E. MORE program.
Maintenance has changed. Experience has shown that with regular Preventive Maintenance, PM, recommended overhauls were lengthened from 800 up to a remarkable 8,000 hours using an FAA STC to Extend Time Between Overhauls, TBO, of type-certified airplanes. Here Maintenance On Reliable Engines, MORE, has an STC regimen for PT6 engines designed to extend engine life through rigid PM involving more frequent periodic condition inspections of components and overall engine health designed to prevent catastrophic and costly repairs.
As an Airplane Repairman, the U.S. Army championed PM decades before the MORE PM existed. As a result, of the many airplanes my crew serviced, I do not recall a single catastrophic major component or engine failure. PM works!
“In the most basic sense, the MORE STC is an aggressive inspection system. The STC increases the frequency and thoroughness of routine engine inspections. The purpose is to find problems in their early stages.”
Millions of hours of operating experience have amply shown that TBOs can be successfully extended up to 8,000 hours.
A key metric to long PT6 life is Engine performance trend data. Think of this like visiting your MD feeling ill. Your physician will narrow down the possibilities, run a few tests, and prescribe treatment. PT6 trend monitoring works essentially the same way. Whatever the symptom and wherever a problem occurs it is likely to show up as a change in performance such as fuel consumption or internal turbine temperature. These red flags tell the technician “Fix me now or soon!”
Experimental aircraft are exempt from mandatory TBOs. https://www.eaa.org/eaa/aircraft-building/intro-to-aircraft-building/frequently-asked-questions/non-builder-maintenance
However, they may obtain an FAA-approved maintenance plan such as N71RJ. This program shifts the emphasis from TBOs to periodic condition inspections. Under this program, parts and components are inspected, and repaired or replaced based on their condition. Parts that are serviceable will continue to operate until the next inspection. For example, this year I installed a new engine oil filter. It has its next inspection in a year. If it is still good, then it can be cleaned and reinstalled – saving the cost of a new one.
My Super Seawind PT6 maintenance schedule has generally followed these MORE standards permitting extension of the TBO to 8,000 hours “on condition” meaning that the N71RJ maintenance program, strictly followed, allows my PT6 to operate to a TBO of 4,505 more hours from today. That’s a huge cost savings over a standard maintenance of a 4,000-hour extended TBO. Bottom line? The N71RJ FAA-approved inspection program enhances safety while dramatically cutting costs.