Accident Details
On April 20, 2016, at about 1130 eastern daylight time, a Bell 47D1 helicopter, registration N202CH, was substantially damaged during practice autorotation landings at Deck Airport (9D4), Myerstown, Pennsylvania. The flight instructor and airline transport pilot were not injured. The helicopter was registered to and operated by a private company. Visual meteorological conditions prevailed, and no flight plan was filed for the local instructional flight conducted under 14 Code of Federal Regulations Part 91.
Flight Sequence
The flight instructor, seated in the right seat, was performing a flight review for the pilot. She reported that she was demonstrating an autorotation that would terminate with power. The instructor entered the maneuver about 1,500 feet above ground level (agl) by reducing the throttle to idle and lowering the collective to the full down position. The carburetor heat was off. She stabilized the approach at 45 miles per hour (mph) but noted the engine's idle speed was about 100 rpm higher than normal. The instructor stated she was not satisfied with the needle split between the engine and rotor rpm, so she advanced the throttle to the full open position. When she did this, there was no response from the engine. The instructor entered a flare about 50 ft agl, and the helicopter impacted the ground with little to no forward speed, bounced, and rolled over to the left.
The pilot stated he was monitoring the instructor's demonstration. They entered the maneuver about 1,200 ft agl and all appeared normal. The pilot was scanning the engine rpm, rotor rpm, and "ball" throughout. When the helicopter reached an altitude of 50 ft agl, he noticed the rotor and engine speed needles were still split, so he reached over and confirmed that the throttle was indeed full open.
Postaccident Examination
A postaccident examination of the helicopter and engine revealed the throttle linkage moved freely from the idle to the full-open position. The engine remained attached to the airframe but had sustained impact damage to several engine mounts and could not be rotated. The ring gear cover at the magneto mount was also broken/cracked. All of the spark plugs were removed and examined, with the exception of the No. 6 cylinder top plug, which was broken off in the cylinder. The spark plugs were bench-tested and each produced a spark. No other mechanical anomalies were noted that would have precluded normal operation of the engine.
Pilot and Instructor Information
The flight instructor held an airline transport pilot certificate for airplane single and multi-engine land, as well as a flight instructor certificate for single and multi-engine airplane, rotorcraft helicopter, and instrument airplane and helicopter. She reported a total flight time of 2,024 hours, of which 590 hours were in helicopters and 31 hours were in the accident helicopter. Her last Federal Aviation Administration (FAA) first-class medical was issued on March 13, 2015.
The pilot held an airline transport pilot certificate for airplane single and multi-engine land, rotorcraft-helicopter, and instrument helicopter. His last FAA second-class medical was issued on May 4, 2015, at which time he reported a total flight time of 14,710 hours.
Weather Conditions
Weather at Muir Army Airfield (KMUI), about 12 miles east of the accident site, at 1208, was wind 200 degrees at 6 knots, visibility 7 miles, clear skies, temperature 64 degrees Fahrenheit (F), dew point 25 degrees F, and barometric pressure 30.26 inches of mercury. A review of the carburetor icing probability chart from FAA Special Airworthiness Information Bulletin (SAIB): CE-09-35 Carburetor Icing Prevention, June 30, 2009, revealed the temperature and dew point reported at the time of the accident were not conducive for the formation of carburetor icing.