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Engine Parts by Catagory

Maintaining Airworthiness

Maintaining Airworthiness

Maintaining airworthiness with HYFAST

This document provides you with basic engine service life information and repair state terminology seen within the industry. All HYFAST engine overhauls strictly follow the standards established by the Federal Aviation Administration and criteria published by the original equipment manufacturer.

Lycoming and Continental Motors both publish engine life limit criteria (see Lycoming SI1009BB and Continental M-0 manual for reference), which is based on their expectation of reliability and minimal operational cost to maintain their products. Airworthiness of your particular engine will depend on which FAR you operate under, and its requirements for compliance of the original manufacturer TBO (time between overhaul) criteria. Highly utilized engines kept within TBO often incur lower overhaul costs than engines operated infrequently or beyond TBO. These “high time” engines can result in excessive component clearances that compound each other resulting in wear on parts which was not originally intended. Corrosion from lengthy improper storage practices can deteriorate internal parts in un-repairable ways requiring replacement thus inflating repair costs during overhaul on engines operated infrequently.    

Aircraft engines are typically offered in 3 ways from an Original Manufacturer: NEW, REBUILT, and OVERHAULED. Although the terminology may change, the difference in the end product remains.

NEW engines are just that; all never run parts built to within new limits with 0 accumulated hours. These are typically used by airframe manufacturers on new aircraft installations and have the greatest cost, doubling that of a “rebuilt” engine.

REBUILT engines provided by the manufacturer are assembled to within new product limits, but will contain used, reworked components like crankcases, crankshafts, connecting rods etc. from other engines. These engines are assembled from the bulk serviceable components on their assembly line and receive your old data plate information before shipment.

OVERHAULED engines are typically provided by the manufacturer as an engine using serviceable parts, but are assembled with those parts within service limits. Service limits are wear limits for units operated in service, and are of a larger specification than new limits, and can reduce the life of serviceability accordingly. This is the lowest cost option provided by the factory, and components may also have less service life.

The terminology also differs for repair stations returning an engine to service. Generally repair stations offer engines or components as OVERHAULED or REPAIRED.

Be mindful that “overhauled” can be certified as airworthy to either “new limits” or “service limits” and the cost should be reflected accordingly. “Repaired” engines only specify the given repair and do not change any accumulated engine time from last overhaul.

As an FAA certified repair station, HYFAST only assembles our engines to within NEW LIMIT specifications, comparable to the original manufacturer’s “rebuilt” engines.


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