LAX03LA130

The airplane collided with obstacles during a forced landing in desert terrain. While in cruise flight, a portion of the propeller blade separated and the airplane's engine began to violently vibrate. The pilot executed a forced landing and the airplane collided with cactus plants prior to touch down. The airplane hit hard and the landing gear separated. The Safety Board's Materials Laboratory examined the remainder of the propeller blade, which revealed fatigue cracking. At the origin of the crack was a corrosion pit. High magnification optical examinations revealed that numerous small shallow corrosion concentration areas were imbedded on both the camber and flat surfaces, in indication that the blade had not been properly dressed. Paint and conversion coatings covered many of the pits and corrosion areas. The propeller was overhauled March 25, 2002, and had accumulated about 700 hours of total time since the overhaul, Logbook entries recorded that maintenance personnel removed propeller nicks on October 30, 2002. FAA Advisory Circular 43.13-1A, Section 3 "Repair of Metal propellers," paragraph 585(a) discusses procedures applied to the repair of aluminum propellers. Specifically, this reference addresses rounding out of nicks, scars, cuts, etc. by advising to "...exercise care to remove the deepest point of the injury..."

On April 6, 2003, about 1000 Pacific daylight time, a Piper PA-28-181, N8465R, collided with obstacles during a forced landing in desert terrain following a loss of a portion of a propeller blade near Baker, California. Air Desert Pacific, Inc., was operating the airplane under the provisions of 14 CFR Part 91. The commercial pilot and one passenger received minor injuries; the airplane sustained substantial damage. The personal cross-country flight departed Brackett Field, La Verne, California, about 0830, with a planned destination of Jean, Nevada. Visual meteorological conditions prevailed, and a flight plan had not been filed. The wreckage was located at 35 degrees 15 minutes north latitude and 116 degrees 3.0 minutes west longitude.

During a telephone interview with a Safety Board investigator, the pilot reported that while in cruise flight, the airplane's engine began to violently vibrate. Thinking that the engine might separate from the airplane, the pilot opted to shut down the engine by manipulating the mixture control to the "off" position. While the pilot was executing a forced landing, the airplane collided with cactus plants about 100 yards south of I-15. During touchdown, the airplane hit hard and the landing gear separated. The wings were also crushed. After egressing the airplane, the pilot noted that a portion of a propeller blade was missing.

The propeller, manufactured by Sensenich Corporation, was a model 74DM6-0-60, fixed pitch, aluminum unit (serial number K34644). The Safety Board investigator-in-charge (IIC) examined the airplane logbooks. The propeller was overhauled March 25, 2002, and had accumulated about 700 hours of total time since the overhaul, Logbook entries recorded that maintenance personnel removed propeller nicks on October 30, 2002.

The missing propeller blade tip was not recovered, however, the IIC shipped the remainder of the propeller blade to the Safety Board's Materials Laboratory, Washington, DC, for further metallurgical examination. The examination revealed radial lines and microscopic fracture traces, which the Senior Metallurgist attributed to fatigue cracking. He stated that the crack initiated at a single location, mid-span on the camber face of the blade. Upon closer inspection he found that a corrosion pit, about 0.010 inches deep, was at the origin of the crack. Further examination indicated that fatigue accounted for approximately 72% of the total fracture area, before final overstress fracture.

High magnification optical examinations revealed that numerous small shallow corrosion concentration areas were imbedded on both the camber and flat surfaces. Remnants of blade paint and conversion coating filled many of the pits . The complete Materials Laboratory Factual Report (Report No. 03-080) is appended in the public docket.

FAA Advisory Circular 43.13-1A, Section 3 "Repair of Metal propellers," paragraph 585(a) discusses procedures applied to the repair of aluminum propellers. Specifically, this reference addresses rounding out of nicks, scars, cuts, etc. by advising to "...exercise care to remove the deepest point of the injury..."

The pilot and operator failed to file or return a Pilot/Operator Aircraft Accident Report, NTSB Form 6120.1/2.