Propellers are subject to wear, fatigue, corrosion and erosion, all of which can lead to failure if not kept in check.

Hartzell Propeller Design, Safety, and Maintenance By Mike Disbrow May-June 1998 Propellers seem to be one of the most visible and yet least respected components on the airplane. They lead a very difficult life, as they are blasted in...

Hartzell developed its aluminum hub or "Compact" series of propellers to offer a lighter weight propeller for general aviation applications. This design consists of a two-piece aluminum hub clamshell arrangement that retains the blades internally. The "Compact" designation comes because retaining the blades internally creates a smaller diameter, more compact package to enclose within the spinner. The pitch change mechanism on this design is contained internally. The blades are rotated via knobs through a fork connected to a piston/cylinder arrangement. The only externally visible component of the pitch change mechanism is the cylinder on the forward end of the hub assembly. While it has evolved through the years, Hartzell has stayed with this basic design due to its proven durability.

A spinner assembly is used to cover the hub assembly and conform to the aircraft cowling. This is a relatively simple component, consisting of a rear bulkhead and the dome. Sometimes a forward bulkhead and a dome cap are required as well. These components are typically manufactured of spun aluminum due to its formability and high strength to weight ratio.

Service Bulletin 217 And AD 97-18-02
In 1997, Hartzell issued Service Bulletin 217 affecting all of its steel hub propellers that utilize double shoulder blades, also referred to as "X" and "V" shank propellers. These propellers are fitted to hundreds of aircraft produced in the 1950s and 1960s, including many Beech, Cessna, Navion, Piper, and Twin Commander models.

In the three years leading up to the issuance of Service Bulletin 217 by Hartzell and AD 97-18-02 by the FAA, there were a growing number of cracked blades, clamps, and hubs reported, as summarized below:
• 37 cracked blades, including two blade separations — one of which resulted in a fatal accident
• 4 cracked blade clamps, including one separation
• 5 blade separations from hub fatigue cracks, all on HC-8 series hubs

From the time the bulletin was issued through the end of January 1998, a significant number of additional cracked components had been discovered:
• 40 cracked blades
• 3 cracked clamps
• 3 cracked hubs, including one blade separation

While most of these additional reports were found during the AD inspection process, one of the cracked hubs was discovered due to blade separation resulting in an aborted takeoff. These results certainly validate the FAA's decision to mandate the inspections called out in Service Bulletin 217 and should provide added impetus for owners and operators to promptly comply with this AD. Failure of the hub, clamp, or blade could result in death or serious injury.

There have been at least four ADs applied to some of these propellers over the past 20 years for similar reasons. They are:

•AD 68-13-02
•AD 68-19-04
•AD 75-17-34
•AD 77-14-07

These ADs were superseded by AD 97-18-02 because they did not cover all of the double shoulder, or "X" and "V" shank propellers, and the inspection procedures and service intervals were not maintaining flight safety.

The failures have been the result of a reduction in the fatigue life of the blade retention system, namely the blades, clamps, and hubs. This is likely due to their extreme age as well as by factors such as corrosion, inaccurate tachometer readings, previous ground strikes, out-of-tune engines, worn crankshaft dampers, and lack of adequate maintenance.

The initial inspection requirement varies from 100 to 200 hours or 24 months from September 1997 when the AD was issued. There is a repetitive requirement of between 250 and 500 hours or 60 months, thereafter. The inspection calls for eddy current inspection of the blade shank. This has proven to be a more effective method for detection of cracks in this area of the blade than the previous dye penetrant method. In addition, other inspection techniques are employed, including optical comparator inspection of the outside profile of the blade shank, dye penetrant inspection of the blade internal bearing bore, and magnetic particle inspection of the clamps and hub.

Hartzell Propeller Design, Safety, and Maintenance

By Mike Disbrow

May-June 1998

Upgrade Available
Hartzell has recently made available a new parts upgrade that eliminates the requirements of AD 97-18-02. While this propeller model will not be listed on most Aircraft Type Certificate Data Sheets (TCDS), the upgrades will be made eligible for these aircraft via amendment to the existing Propeller TCDSs.

Service Bulletin 232 "Introduction of MV Shank Propellers," issued March 20, 1998, provides general information about the improved propeller design, including application, propeller model, and pricing data. Service Bulletin 233 "Conversion of V Shank Propellers to MV Shank," issued April 17, 1998, provides the requirements for upgrades of existing propellers in the field.

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