N7395Grumman G-164A · 1972

On July 12, 2008, about 0959 eastern daylight time, a Grumman G-164A, N7395, was substantially damaged when it impacted terrain in Pelham, Georgia. The certificated commercial pilot was fatally injured. The aerial application flight was operated under the provisions of 14 Code of Federal Regulations (CFR) Part 137. Visual meteorological conditions prevailed for the flight, and no flight plan was filed.

On June 28, 2008, the pilot reported propeller control problems with the airplane, and the next day, a mechanic from Florida drove to Pelham to perform maintenance on the engine. The maintenance was completed on July 2, and the pilot began using the airplane again that same day. Investigators could not ascertain how many flights or engine hours the airplane accrued between July 2 and July 12.

On the morning of the accident, one witness who was located approximately 2 3/4 miles north-northwest of the accident site, said that as the airplane flew past her, it sounded like a helicopter, and that the engine was making "popping" noises. Another witness who was working in a field near a pond, observed the airplane circle the pond twice before he saw it "go down." The witness headed towards the presumed impact location, saw that the airplane "had crashed," and that it was on fire. The witness then notified local emergency authorities.

Pilot

According to FAA records, the pilot held a commercial pilot certificate with airplane single and multi-engine land ratings. He was prohibited from carrying passengers for hire at night, or on cross-country flights of more than 50 nautical miles. The pilot reported 24,800 total hours of flight experience on his most recent second-class medical certificate, which was issued in August 2007. The pilot was also the owner of a company that was certificated for aerial agricultural application under 14 CFR Part 137. The certificate was issued in July 1989, and the most recent validation date for the certificate was June 2008.

Engine Mechanic

The mechanic who performed the last known maintenance activity on the engine held a mechanic's certificate, with airframe and powerplant ratings. He was employed by a maintenance provider in Florida that specialized in servicing the aerial application industry, and Pratt & Whitney radial engines. The mechanic had been employed by this organization for at least 10 years. He was also a personal and professional acquaintance of the pilot for approximately 40 years.

The accident airplane was manufactured in 1972. Maintenance records indicated that a major overhaul was conducted on the Pratt & Whitney R-1340 engine in July 2005, and the corresponding logbook entry listed the time since major overhaul (SMOH) as "00:00" hours. This engine remained installed in the airplane until the accident.

In September 2005, with an engine SMOH of approximately 202 hours, the number two cylinder was removed to conduct maintenance on the exhaust valve guide, and the cylinder was then re-installed on the engine. In October 2005, with an engine SMOH of approximately 300 hours, the number three cylinder was removed due to a crack, and was replaced with an overhauled cylinder. In March 2006, with an engine SMOH of approximately 383 hours, the number three cylinder was again removed and replaced with an overhauled cylinder.

Between August 9 and December 29, 2005, the maintenance records indicate that the oil was drained, and the oil screens were checked for contamination, on four separate occasions. These occurred at approximately 38, 101, 193 and 382 hours SMOH, respectively. The next documented oil drain and screen check occurred on April 27, 2008, at an SMOH of 601 hours. No contaminants were noted in any of the corresponding log entries.

Maintenance records documented two annual inspections since the installation of the accident engine. The first was on March 7, 2006, and the second was on May 2, 2008. The SMOH times for these inspections were 383 and 601 hours, respectively.

The last known engine maintenance was completed on July 2, 2008. According to the mechanic who conducted the maintenance, he was based approximately 130 miles from the airstrip where the airplane was located, which was also where the maintenance was conducted. The maintenance was conducted outside, and on occasion had to be suspended for inclement weather.

The maintenance activity included the removal of seven of the nine cylinders; cylinders two and seven were not removed. During the maintenance activity, fragments of piston rings and a piston skirt, as well as a broken governor drive gear, were discovered in the engine case. The engine was pressure-cleaned with mineral spirits and reassembled. Six of the removed cylinders were re-installed with "serviceable" pistons, and the number one cylinder was replaced with an overhauled cylinder and a new piston. The airplane was successfully test flown after the maintenance was completed.

The airplane was first registered to the accident pilot in April 2008.

The 1000 surface weather observation at an airport located approximately 30 miles east of the accident site reported winds from 350 degrees at 5 knots, visibility 10 miles, scattered clouds at 1,300 feet and 1,800 feet, broken clouds at 8,000 feet, temperature 26 degrees C, dew point 22 degrees C, and an altimeter setting of 30.13 inches of mercury.

The accident site was a small grassy clearing in a wooded area, located approximately 6/10 of a mile north-northwest of the private airstrip where the airplane was based, and along a course between the field which had been sprayed and the airstrip. The first ground scars were two parallel scrapes approximately 13 feet long and 6 feet apart. These scars were oriented on a southeast heading. The second and last prominent ground scar began 17 feet beyond the end of the parallel scrapes. It was approximately 8 feet wide and 14 feet long. Numerous small airplane fragments were distributed in the proximity of the ground scars. The majority of the wreckage was tightly contained at the base of the trees that bounded the clearing, approximately 16 feet beyond the end of the second ground scar.

The airplane came to rest inverted, facing back towards the debris path and ground scars. The wings were partially separated from the fuselage, and the forward fuselage exhibited significant crushing and other distortion. The wreckage exhibited considerable fire damage. Flight control continuity was not verified on scene. The engine was mechanically separated from the fuselage, but remained with the wreckage. The propeller remained attached to the engine. Both propeller blades were bent aft. The engine and airframe were retained for additional examination.

The pilot did not indicate the use of any medications, or the diagnosis of any medical conditions, on his most recent application for his FAA second-class medical certificate, which was dated August 2, 2007. On that application, his height was noted as 72 inches, and his weight was noted as 278 pounds.

Toxicological testing was conducted by the FAA Civil Aero Medical Institute (CAMI). Test results were negative carbon monoxide, cyanide, or ethanol. The testing detected Meteprolol in the pilot's blood, and Ephedrine, Meteprolol, Naproxen, Pseudoephedrine and Salicylate in the pilot's urine.

An autopsy was performed by a medical examiner from the Georgia Bureau of Investigation. The cause of death was noted as "Traumatic injuries complicating cardiomegaly and coronary atherosclerotic disease." The autopsy noted that "the heart is enlarged and weighs 540 grams. The chambers of the right side of the heart are dilated. … The myocardium exhibits gray-white scarring involving the apical region of the anterior left ventricle. … The left ventricular free wall has a maximum thickness of 1.5 cm with thinning of the anterior scarred area which measures 1.0 cm. The coronary arteries have a normal origin and distribution and exhibit severe atherosclerosis with all three of the major coronary arteries exhibiting greater than 95% luminal narrowing."

Detailed Engine Examination

On July 23 and 24, 2008, the engine was examined at a storage facility. Several FAA inspectors participated in this activity, with the assistance of mechanics provided by the storage facility. The examination results were documented in digital photographs and an FAA memorandum dated July 25, 2008. Subsequent to that examination, several components of interest were provided to the National Transportation Safety Board (NTSB) for additional examination. The following paragraphs summarize the findings from the examinations.

Upon recovery, the engine was caked with dirt, and exhibited some fire damage. Items damaged by fire included one magneto, the accessory area, and the end of one propeller blade. All cylinders were removed from the engine. The number one cylinder and piston appeared newer that the other cylinders and pistons.

Each piston was normally equipped with five rings. The top three rings were the compression rings, the fourth was the oil control ring, and the bottom ring was the oil scraper ring. The two top compression rings did not have any chamfered faces, while the outer face of the third compression ring was chamfered. The oil-control ring had two outer faces separated by a groove at mid-height, and the outer face of the oil scraper ring was also chamfered.

The number two cylinder appeared normal, but the bottom side of the piston, which was exposed to the crankcase, had numerous sharp-edged dents consistent with impact marks from metal fragments. Similar damage was observed on the bottoms of pistons four and eight, and the damage to piston eight was the most severe of the three.

Portions of the underside and inner perimeter of piston four's skirt also exhibited relatively fresh machining marks which were not discolored by oil coking. The oil scraper ring from piston four was fractured in multiple locations, and fell off the piston when it was removed from the cylinder. The largest remaining fragment constituted an arc of approximately 180 degrees. The scraper ring land was also damaged, and some of the damage extended to the bottom of the piston skirt. Some scoring was noted on the skirt of piston eight.

Pistons three, five, six, seven and nine did not exhibit any dents on their undersides. In addition, these pistons did not exhibit any significant coking. The oil scraper ring from piston five was fractured, but the largest fragment was sufficiently intact to remain on the piston when the piston was removed from the cylinder. This fragment had one finished end and one fractured end, and constituted an arc of approximately 280 degrees. This fragment was accidentally fractured during shipment to NTSB, and for reference purposes, the two fragments were subsequently designated as "A-1" and "A-2" by the investigator in charge. The other rings on piston five, and all the rings on the remaining pistons, were intact and unremarkable.

The engine nose dome was opened, and "trace metal" was noted by the FAA inspectors. In addition, a 1/4 inch long fragment of a piston ring was found on a web near the cam gears. The fragment was designated "X.". The engine case halves were then split, and impact marks similar to those observed on the piston bottoms were noted on the case half interior surfaces and the crankshaft counterweights. The accessory and supercharger section was opened, and five piston ring fragments (designated "B" through "F"), and three gear teeth, were found loose inside the section.

The carburetor exhibited heat damage from the post-impact fire. The mixture control arm remained attached to the carburetor and retained its rod end, but the mixture control rod was fracture-separated approximately 2 inches from its attach point on the mixture arm. The throttle arm remained attached to the carburetor, but the throttle control rod was not attached to the throttle arm. The bolt that connected the rod end to the arm remained installed in the arm, but was bent approximately 80 degrees. The castellated nut was not on the bolt, and the cotter key hole in the bolt did not appear deformed. The bolt threads surrounding the cotter key hole were significantly flattened and/or stripped.

Piston Ring Fragments

A total of eleven piston ring fragments were recovered. Collectively, these fragments did not constitute sufficient material to reconstruct two complete oil scraper rings, in order to account for the fractured rings from pistons four and five.

The five largest fragments (including the fragment from piston four, and the four others designated as "A-1" through "A-4") had chamfered outer faces. Each of the other six ring fragments was less than 1/2 inch long, and exhibited multiple dents, nicks, and other deformation on all facets. The damage to the six fragments precluded a determination of whether they had chamfered outer faces. The heights of all fragments were measured with a micrometer, and all were the same height when measured in units of inches to a resolution of three decimal places.

Two of the fragments (A-3 and A-4) were from an oil scraper ring, and together they constituted an arc of approximately 60 degrees. These fragments mated to one another, and one of them (A-4) had a finished end that complemented the finished end on A-1 from piston five. However, the fractured end of the other fragment (A-3) did not match the fractured end of A-2, which precluded positive determination that these two fragments were from the oil scraper ring from piston five. Even if it was assumed that fragments A-3 and A-4 were from piston five, an overlay of fragments A-1, A-2, A-3 and A-4 on an intact oil scraper ring indicated that approximately 1/4 inch of the ring was still unaccounted for. None of the fracture faces on the other six candidate fragments ("B" through "F," and "X") could be matched to the fracture faces on either A-2 or A-3.

Collector Intermediate Gear

The collector intermediate gear was housed in the aft engine section, and consisted of two externally-toothed gears on a common axis. The larger gear was 5 1/4 inches in diameter, 13/16 inches wide, with a pitch of approximately 4 teeth per inch. The smaller gear was 2 inches in diameter, 1 inch wide, with a pitch of approximately 2 1/4 teeth per inch. The smaller gear of the collector intermediate gear was driven by the floating gear, which was driven by the crankshaft. The larger gear of the intermediate collector gear drove the impeller gear for the supercharger.

The dimensions and fracture lines of the three tooth fragments found in the accessory section corresponded to the three missing, adjacent teeth on the smaller gear. Examination of the smaller gear by the NTSB Materials Laboratory revealed that the same flanks on all the intact and fractured gear teeth displayed wear from contact with the teeth of the mating gear during normal operation, and that some pitting was present on each of these flanks. When the collector intermediate gear was viewed along its axis so that both gears were visible, the worn tooth flanks faced in the counterclockwise direction. However, the fractures of the three separated teeth were also in the counterclockwise direction; the fracture direction was from the unworn flank towards the worn flank. The clockwise-facing flanks of the fractured teeth exhibited gross deformation. The fractures did not exhibit any signs of fatigue or other pre-existing failure. The collector intermediate gear teeth fracture directions and types were consistent with a sudden stoppage of the engine. According to the Pratt & Whitney overhaul manual, these gears must be scrapped when an engine experiences a "sudden stoppage or shock loading." Examination of the maintenance records did not reveal any sudden stoppage inspections.