Accident Overview
On May 3, 2014, at about 0915 Pacific daylight time, a Bell 47G helicopter, registration N7895B, sustained substantial damage during a precautionary landing approximately 3 miles south of El Monte Airport (EMT) in El Monte, California. The helicopter was registered to and operated by the pilot under 14 Code of Federal Regulations Part 91. The private pilot and a passenger sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the personal cross-country flight, which originated at EMT about 0910 with a destination of Compton/Woodley Airport in Compton, California.
Pilot's Account
The pilot reported that during climb out, at about 600-700 feet above ground level, the engine experienced a partial loss of power. The helicopter shook violently, and the engine emitted a couple of popping sounds. The pilot immediately initiated a precautionary landing in an open field. During the landing, the pilot carried a little forward speed, causing the right skid to catch on the ground, which rolled the helicopter onto its right side.
Examination Findings
An examination of the helicopter by the pilot revealed that the fuselage and main rotor blades were structurally damaged. The wreckage was recovered to a local storage facility for further examination. A certified airframe and powerplant (A&P) mechanic, under the supervision of the National Transportation Safety Board investigator-in-charge, examined the recovered airframe and engine. The engine remained attached through all of its mounts. The carburetor was intact and disassembled, with all internal components intact. The top spark plugs were removed, and the engine was rotated by hand. Thumb compression was obtained on all cylinders, and proper valve movement was observed. All engine control continuity with the cockpit controls was established.
Both magnetos were intact and removed for functional testing on a test bench. The right magneto functioned normally, producing a spark at all leads during various rpm settings. The left magneto did not function properly; at low rpm, no spark was observed, and at higher rpm, spark was intermittent and firing at random. Disassembly of the left magneto revealed that the internal rotor was loose from its attachment.
All spark plugs functioned normally during functional checks, except those from the number 5 cylinder. The top spark plug had heavy carbon deposits in the electrode area and produced no spark. The lower spark plug had corrosion in the electrode area and exhibited thermal damage to the electrode.
Maintenance Records
Review of the helicopter's maintenance records showed that the engine and airframe underwent their most recent annual inspection on August 28, 2013, at an engine total time of 537 hours and an airframe time of 2,726 hours.