WILMOT, AR, USA
N634U
Grumman G-164
Pilot initiated a forced landing following a total loss of engine power. Examination revealed a fractured throttle cable due to excessive wear & fatigue cracking. The fractured area of the cable was not accessible for inspection due to its location within the cable housing. The 1965 aircraft had accumulated 10,001.96 hours. No evidence was found that the throttle cable had ever been replaced. Mid-afternoon, the pilot felt nauseated; however, he continued the aerial application flights. A land owner found the airplane upside down in a cotton field and called 911. Seat belt/shoulder harness was not worn. Autopsy results indicated the pilot's cause of death as 'acute thrombosis of the left anterior descending coronary artery complicated by multiple injuries sustained in the accident. The pathologists reported that the autopsy demonstrated evidence of compressional asphyxia.'
HISTORY OF FLIGHT On August 10, 1997, at 1945 central daylight time, a Grumman G-164 agricultural airplane, N634U, owned by J. & J. Salvage, Inc., of Lake Providence, Louisiana, and operated by Wilmot Aviation, Inc., of Wilmot, Arkansas, under Title 14 CFR Part 137, sustained substantial damage during a forced landing near Wilmot, Arkansas. The commercial pilot received fatal injuries. Visual meteorological conditions prevailed for the local aerial application flight and a flight plan was not filed. The flight departed the operator's private airstrip at Wilmot Aviation, Inc., at approximately 1900. During personal interviews, conducted by the investigator-in-charge (IIC), the aircraft owner and personnel of the operator reported the following information. Rain showers moved through the area during the morning; however, by noon the weather was clear with calm winds and a temperature of 85 degrees Fahrenheit, and the pilot began his daily flights. About mid afternoon, during reloading of the chemicals, the pilot mentioned to the loader that he was feeling nauseated. The pilot went to his truck and when he returned to the airplane, he stated that he felt better and was ready to fly. The last job of the day was 165 acres and required 4 loads (trips) of chemicals. When the pilot returned from dispensing the second load, he mentioned that he heard a sound and thought maybe the airplane "blew a cylinder." After inspecting the engine for oil leaks and finding none, the pilot departed with the third load of chemicals and upon the return from dispensing that load, he stated that the airplane flew "OK." The pilot was dispensing his last load for the day when the accident occurred. During interviews conducted by local authorities and the IIC, witnesses reported hearing the airplane flying throughout the early evening; however, due to the smell of the chemicals they remained inside their homes. A land owner driving in the area, found the airplane upside down in the cotton field and called 911. PERSONNEL INFORMATION The FAA records reviewed by the IIC revealed that the pilot obtained his second class medical on February 2, 1997. On the medical application, the pilot listed his total flight time as 15,009 hours at the time of the medical application. On the Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2) the operator listed 20,000 hours of pilot in command time with 10 hours in make and model. During personal interviews, conducted by the IIC, the aircraft owner and personnel of the operator reported that the pilot had accumulated over 15,000 hours of flight time performing aerial applications. Since January 1997, the pilot had flown the Dromadier M18 for 304 hours during aerial application flights for this operator. Due to maintenance on the Dromadier, the pilot flew the Grumman on the day of the accident. The operator stated that the pilot "never wore a seat belt/shoulder harness or helmet." AIRCRAFT INFORMATION Maintenance records reviewed by the IIC revealed that aircraft, N634U, serial number 370, was manufactured in 1965 by the Schweizer Aircraft Corporation, at Elmira, New York, for Grumman. The original engine installed was a Jacobs R-755-A21M. The original FAA airworthiness certificate was issued on July 26, 1965. There were different Jacob engines installed on the aircraft, respectively from 1965 through 1974. After 1974, various P&W R-985-AN1 engines were installed per STC SA 39WE. On March 2, 1994, the P&W R-985-AN1 engine, S/N 20854 (Air Force Bureau 43-4668), was installed on the airframe of N634U. During the June 1995 annual inspection, the carburetor exhaust heat muff was installed, the mixing box was removed and disassembled, and the carburetor heat cable was replaced. The last annual inspection was performed in March 1997 at a total aircraft time of 10,0001.96 hours (tachometer 51.8 hours). At this annual inspection, the engine (873.0 hours SMOH, 197.7 hours STOH) was removed and re-installed after replacing an engine mount bolt. There were no records found indicating that the throttle cable had ever been replaced. The IIC requested throttle cable specifications, installation, and inspection procedures from Schweitzer. As of this writing, the requested information has not been received. WRECKAGE AND IMPACT INFORMATION Bean fields were adjacent to the cotton field that was being sprayed by the pilot. Tracks consistent with the right wing and the main wheels of the aircraft extended through the bean field, across a ditch, across a road, and southward through a cotton field where the aircraft came to rest inverted on a measured magnetic heading of 060 degrees. The aircraft came to rest approximately 400 feet from the point of initial ground impact. See the wreckage distribution diagram for additional details. Hazardous chemicals (Curacron 8E and Azinphosmethyl 2 EC) spilled at the site limited the field investigation. The aft empennage, rudder, and vertical stabilizer sustained impact damage. Flight control continuity was confirmed. Fuel was leaking from the fuel tank and 22 gallons of fuel were drained from the tank. The seat belt and shoulder harness were unfastened. Tachometer reading was 84 hours. The fuel selector was in the "on" position. The magneto switch was in the "both" position. The control quadrant showed the throttle lever full forward. One propeller blade was bent aft at the outboard end and the second propeller blade was bent and twisted aft at the outboard end. MEDICAL AND PATHOLOGICAL INFORMATION The autopsy was performed by the Arkansas State Crime Laboratory, at Little Rock, Arkansas. The autopsy listed the cause of death as an "acute thrombosis of the left anterior descending coronary artery, complicated by multiple injuries sustained in the accident. The pathologists reported that the autopsy demonstrated evidence of compressional asphyxia which included multiple petechial and conjunctival hemorrhages, bilateral periorbital petechial hemorrhages and there was plethora of the facies and neck with bilateral venous neck distention. Another significant finding was an acute thrombus involving the left anterior descending coronary artery. The heart was slightly enlarged." Aviation toxicological testing was performed by the FAA Civil Aeromedical Institute (CAMI) at Oklahoma City, Oklahoma. Toxicological findings were positive for acetaminophen. According to Dr. Canfield, CAMI, the 40.900 (ug/ml, ug/g) acetaminophen (Tylenol) detected is insignificant. See the toxicological report for details. TEST AND RESEARCH On September 5, 1997, engine S/N 20854 was examined under the surveillance of an NTSB investigator at Arkansas Airframe, Clinton, Arkansas. It was noted that the carburetor throttle arm was in the idle position while the quadrant in the cockpit had the throttle control level in the wide open position. The throttle cable is enclosed by a cable housing. It was found that when the throttle push pull control was moved that it did not move the throttle arm at the carburetor. When the bolt and nut holding the ball end of the cable at the carburetor arm were removed, the ball end and about 8 inches of the push pull control came free of the cable housing. The area of the cable that fractured was not accessible for inspection. The throttle cable routing from the cockpit throttle quadrant to the carburetor involved two 90 degree change of directions. According to personnel at Schweitzer, this routing was within the guidelines of the maintenance manual. The cable is a condition item, without a mandatory replacement time. The cable was forwarded to the NTSB Metallurgical Laboratory for examination. For the engine run, a wire was installed on the throttle arm of the carburetor to operate the carburetor and a test propeller was installed. Duration of the engine run was 20 minutes at various power settings. No additional discrepancies were noted that would have contributed to a loss of engine power. See the enclosed report for additional details. The fractured surfaces of the throttle cable were examined at the NTSB Metallurgical Laboratory. The metallurgists reported that visual examination of the fractured ends revealed excessive wear on the outer fitting and the inner strands of the steel wires. A scanning electron microscope (SEM) image of the fractured end revealed that fatigue cracking originated from the surface of the wire. The fractured features of the remaining wires were obliterated due to rubbing damage. See the metallurgist's report for additional details. ADDITIONAL INFORMATION The aircraft was released to the owner's representative.
The loss of engine power due to a fractured throttle cable because the cable housing prevents an inspection of the cable by maintenance personnel. Factors were the pilot's impairment due to a heart attack, the lack of suitable terrain for the forced landing, and the pilot's failure to use the seat belt/shoulder harness.
Source: NTSB Aviation Accident Database
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