TO: ALL AIRCRAFT OWNERS, AIRFRAME MANUFACTURERS, FAA APPROVED PROPELLER REPAIR STATIONS, AND SENSENICH DISTRIBUTORS.
SUBJECT: INCREASE OF TBO (TIME BETWEEN OVERHAUL/ RECONDITIONING CYCLE) FROM, 1000 HOURS TO 2000 HOURS.
PROPELLER MODEL(S): ALL SENSENICH FIXED-PITCH ALUMINUM PROPELLER MODELS
AIRCRAFT MODEL(S) AFFECTED: ALL AIRCRAFT
On August 20, 1997 the New York Aircraft Certification Office approved Sensenich’s request to increase its fixed-pitch aluminum propeller TBO time from 1000 hours to 2000 hours.
The chart below provides the recommended TBO times for Sensenich fixed-pitch aluminum propellers. These times depend greatly on the operating environment to which the propeller is exposed. Flight school operations, unpaved runways, or poorly maintained runways may expose the propeller to increased foreign object damage that will require a shorter interval between overhauls in order to remove damage that could potentially cause a blade failure.
|Aircraft Operation (Category)
||Total Flight Hours
|Normal and Utility Operation
|* Provided it has not received damage requiring immediate attention or superseded by Airframe Manufacturer
The approval of the TBO increase was a result of the extensive study that Sensenich completed and submitted to the FAA NYACO on propeller service histories, finish systems, and propeller failure histories. During this study, we found that Sensenich propellers (since their development in 1948) have had an extremely low percentage (.09%) of blade failures compared to the number produced. The highest percentage of these failures are directly attributed to conditions that have been addressed by Sensenich Airworthiness Directives, of which Sensenich only has four (4). Since the last Sensenich Airworthiness Directive 69-09-03, published in 1969, 90% of the failures that have occurred are directly attributed to one of the following:
Modification Below T.C. Limits –
These modifications include diameter reductions, straightening of higher than allowable blade bends, blade shape and or airfoil changes, and twisting of blade angle to higher than approved pitches.
Improper Repairs –
Improper repairs include any repairs not completed to the most current Sensenich repair manual. These improper repairs may be any of the following
- Reduction of chord or thickness below published minimum repair values,
- Poor overhauls that do not remove all damage or do not remove damage correctly,
- Straightening of higher than allowable blade bends,
- Not completing a reconditioning after blade straightening, or
- Twisting of blade angle too higher than approved pitches.
Poor Maintenance –
Poor maintenance refers to the lack of maintenance by owner/operator. Damage such as leading edge nicks and cuts, face nicks and cuts or corrosion that are left unrepaired and or painted over without proper removal and re-application of a corrosion coating are considered poor maintenance.