MV propeller upgrade eliminating recent Airworthiness Directive

Citation

(1998), "MV propeller upgrade eliminating recent Airworthiness Directive", Aircraft Engineering and Aerospace Technology, Vol. 70 No. 5. https://doi.org/10.1108/aeat.1998.12770eaf.007

MV propeller upgrade eliminating recent Airworthiness Directive

"MV" propeller upgrade eliminating recent Airworthiness Directive

Keywords Airworthiness, Hartzell Propellers, Upgrade

Hartzell Propeller Inc. has announced the availability of a new parts upgrade that eliminates Airworthiness Directive (AD) 97-18-02 affecting various Beech, Cessna, Navion, Piper, Twin Commander and other aircraft from the 1950s and 1960s. The new upgraded propeller model will be designated H(A or C)-(A or D)(2 or 3)MV()-() (see Figure 1, comparing with previous V-shank model). 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.

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 being found, as summarized below:

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  37 cracked blades, including two blade separations, one which resulted in a fatal accident;

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  four cracked blade clamps, including one separation;

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  five blade separations from hub fatigue cracks, all on HC-8 series hubs.

Figure 1 Comparison of the two style blade retention systems

Since the bulletin was issued until the end of January 1998, a significant number of additional cracked components have been discovered:

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  40 cracked blades;

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  three cracked clamps;

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  three 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 take-off. 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.

Service Bulletin 232 "Introduction of MV Shank Propellers", issued 20 March 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 17 April 1998, provides the requirements for upgrades of existing propellers in the field. As previously announced, the upgrade converts the double shoulder design of the X and V-shank blades to a single shoulder design, similar in configuration to Hartzell's proven steel hub turbine propellers. This is to be accomplished by either reworking existing blades according to the requirements of Service Letter 182 or replacing the blades with those manufactured in the MV configuration as new.

Service Letter 182, also issued 17 April 1998, was developed specifically to create a method to modify existing blades in the field, however, the process or re-contouring of the outboard shoulder is difficult and will be limited to selected propeller repair stations utilizing highly skilled machinists. Hartzell will begin working with these shops to develop this capability. On modified blades, the inboard shoulder, where most of the cracks have been discovered, will no longer be load bearing.

In order to accommodate the single shoulder MV blade, new blade retention clamps are required. The wall and outboard flange thickness of the new clamps has been increased to retain the single shoulder blade. In addition, this upgrade will only be applicable to HC-A or D style hubs. Operators with HC-1 or -8 style hubs will need to purchase the A or D style hub and associated parts.

Owing to the design improvements provided by this upgrade, not only are the requirements of the AD eliminated, but also the recommended time between overhaul (TBO) has been increased to 2,000 hours or five years. Operators are urged to adhere to these recommendations to maintain the benefits of this new design.

For further details contact Hartzell Propeller Inc., USA. Tel: +44 (1) 937 778 4310; Fax: +44 (1) 937 778 432; E-mail: disbromi@erinet.com