SPECIAL AIRWORTHINESS INFORMATION BULLETIN
Aircraft Certification Service
Washington, DC
U.S. Department of Transportation
Federal Aviation Administration
NE-08-20

May 14, 2008

This is information only. Recommendations aren’t mandatory.

Introduction

This Special Airworthiness Information Bulletin (SAIB) alerts owners, operators, pilots, mechanics, and certificated repair facilities of concerns for possible failures of variable pitch propellers due to inadequate propeller maintenance.

The FAA is concerned about the continued airworthiness of propellers with regard to maintenance performed on Part 91 of the Code of Federal Regulations (14 CFR part 91) General Aviation aircraft.

Propellers are generally very safe and reliable. Because of this, propeller maintenance may be perceived as not requiring as much scrutiny as engine maintenance. Propeller failures are relatively rare, but when a propeller fails, the consequences are typically more severe than when an engine fails and could result in damage to the engine and mount, and loss of aircraft control.

Background

14 CFR Part 91 Requirements

It is established that 14 CFR part 135 and 14 CFR part 121 operators are held to a higher standard of maintenance than 14 CFR part 91 operators. With regard to propellers, this generally means that for 14 CFR part 91 operators, compliance with manufacturer’s overhaul recommendations is not mandatory. Indeed, it is reported by propeller repair stations that they occasionally see propellers coming in for service that have no evidence of maintenance or overhaul history for as long as twenty years or more.

To Overhaul or Not To Overhaul

The FAA does not mandate compliance with the manufacturer’s recommended overhaul intervals for 14 CFR part 91 operators. However, compliance is recommended.

Service experience has shown that by neglecting propeller maintenance and not performing timely overhauls or repairs can result in a propeller failure. A failure that originates from corrosion is preventable. Seemingly small areas of corrosion can generate stress concentrations which can initiate fatigue cracks.

Evident Versus Hidden Conditions

Propeller blades can and often do sustain considerable wear and damage in service. Propeller blades are often observed to have evidence of nicks, gouges, corrosion, or other surface flaws that should not be ignored and left uncorrected. Operators, mechanics, and aircraft inspectors need to recognize that conditions such as this demand action regardless of the flight time since last overhaul. The propeller manufacturer’s Instructions for Continued Airworthiness and FAA Advisory Circular AC 20-37E Aircraft Propeller Maintenance (revised 9/9/05) provide additional information on this subject.

Another concern is reports of painting propeller blades in the field where nicks, gouges, corrosion, or other surface flaws are covered over. A cosmetically attractive paint job can hide a serious structural flaw and cause an airworthiness issue later on.

Controllable pitch propellers have internal components that cannot be inspected without disassembly. Unlike oil/grease leaks, degradation of grease or seals, etc. that may be evident, internal corrosion problems are often hidden and cannot be evaluated without disassembly and inspection. Hidden defects in highly stressed areas of the hub or other blade retention components can lead to fatigue cracks, blade separation, and loss of airplane control. This is the primary reason why propeller maintenance requirements contain calendar limits.

Manufacturer’s Overhaul Calendar Limits

A common complaint from the field is that manufacturer’s flight hour limits for overhaul may be reasonable but calendar limits seem too onerous for low utilization, general aviation aircraft.

The extent of exposure and types of corrosive elements can vary greatly. An appropriate time limit for development of corrosion is hard to predict. However, it can be shown that propeller failure events attributed to corrosion typically occur in propellers that are either NOT in compliance with the manufacturer’s overhaul calendar limits, have NOT been properly maintained, or have NOT been properly overhauled.

Recommendations
Performing these actions will reduce the opportunities for the propeller to be a causal factor in an accident.

For Further Information Contact

Jay Turnberg, Propeller Specialist, Standards Staff, FAA, Engine and Propeller Directorate; 12 New England Executive Park, Burlington, MA 01803; e-mail: jay.turnberg@faa.gov; phone: (781) 238-7116; fax: (781) 238-7199.

For Hamilton Sundstrand, Avia, Dowty, Hoffmann, or MT Propellers:
Terry Fahr, Aerospace Engineer, Boston Aircraft Certification Office, FAA, 12 New England Executive Park, Burlington, MA 01803; e-mail: terry.fahr@faa.gov; phone: (781) 238-7158; fax: (781) 238-7170.

For Hartzell Propellers:
Tim Smyth, Aerospace Engineer, Chicago Aircraft Certification Office, FAA, Propulsion Branch, 2300 East Devon Avenue, Des Plaines, IL 60018; e-mail: timothy.smyth@faa.gov; phone: (847) 294-7132, fax: (847) 294-7834.

For McCauley Propellers:
Jeff Janusz, Aerospace Engineer, Wichita Aircraft Certification Office, FAA, Propulsion Branch, 1801 Airport Road, Room 100, Wichita, KS 67209; e-mail: jeff.janusz@faa.gov; phone: (316) 946-4148; fax: (316) 946-4107.

For Sensenich Propellers:
James Delisio, Aerospace Engineer, New York Aircraft Certification Office, FAA, Propulsion Branch, 1600 Stewart Avenue, Suite 410, Westbury, NY 11590; e-mail: james.delisio@faa.gov;
phone: (516) 228-7321; fax: (516) 794-5531.

For Related Service Information Contact

Avia Propeller Ltd., Beranových 666, 199 00, Prague – Letňany, Czech Republic; phone: +420/0/2/9633 6530 or 31; fax: +420/0/2/9633 6519 or 33.

Dowty Propellers, Anson Business Park, Cheltenham Road East, Gloucester GL 2 9QN, UK; phone: 44 (0) 1452 716000; fax: 44 (0) 1452 716001.

Hamilton Sundstrand, One Hamilton Rd, Windsor Locks, CT 06095; phone: (860) 654-6822; fax: (860) 654-5107.

Hartzell Propeller Inc., Hartzell Propeller Product Support, Attn: Product Support; One Propeller Place, Piqua, OH 45356-2634; phone: (937) 778-4379; fax: (937) 778-4391 (Intl. 001.937.778.4391).

Hoffmann GmbH & Co.KG, Kuepferlingstr. 9, D-83022, Rosenheim, Germany; phone: +49-8031-1878-0; fax: +49-8031-1878-78.

McCauley Propeller Systems, P.O. Box 7704, Wichita, KS 67277-7704; phone: (800) 621-7767; fax: (316) 831-3858.

MT-Propeller Entwicklung GmbH, Flugplatzstr. 1, D-94348 Atting, Germany; phone: +49-(0)9429-94090; fax: +49-(0)9429-8432.

Sensenich Propeller Manufacturing Company, Inc., 14 Citation Lane, Lititz, PA 17543; phone: (717) 569-0435; fax: (717) 560-3725.