Accident Details
On April 28, 2009, at about 1500 Alaska daylight time, a Piper PA-24-180 airplane, registered as N7352P, experienced a forced landing after a reported loss of engine power while on approach to Birchwood Airport in Chugiak, Alaska. The aircraft, equipped with a Lycoming O-360-A1A engine, was substantially damaged. The certificated flight instructor and the private pilot, who was also the airplane owner, were not injured.
The flight was conducted as a visual flight rules (VFR) instructional flight under Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed. The flight originated from Merrill Field Airport in Anchorage, Alaska, about 1450.
Flight Sequence
According to the flight instructor, he was seated in the right seat while the private pilot occupied the left seat. The purpose of the flight was to administer a biennial flight review to the pilot, whose previous review had expired. After departing Merrill Field, they flew north at 1,600 feet msl. As the airplane approached Birchwood Airport, the instructor closed the engine throttle, simulating an engine failure, and instructed the pilot to demonstrate an emergency descent and landing. The pilot followed emergency procedures, entering a right base for Runway 1L.
During the simulated emergency descent, as the airplane turned from base to final, the instructor momentarily advanced the throttle to confirm engine power was still available; the engine responded accordingly. However, on short final for Runway 1L, the pilot lowered the landing gear, and the airplane's descent rate increased significantly. The instructor commanded a go-around, and the pilot applied full throttle, but the engine did not respond. The instructor confirmed the throttle was fully open. The pilot then pulled aft on the control yoke to cushion the landing on grass-covered terrain. During the forced landing, the airplane struck a perimeter fence and slid for several feet. The nose and main landing gear collapsed, and substantial damage occurred to the fuselage and wings.
Both pilots reported that carburetor heat was not used during the simulated emergency descent and approach.
Weather Conditions
At 1453, the Birchwood Airport METAR reported wind from 310 degrees true at 5 knots, visibility 10 statute miles, clear skies, temperature 54°F, dew point 32°F, and altimeter 30.39 inHg. The airport is adjacent to Cook Inlet. The temperature and dew point, when entered into a carburetor icing probability chart, fell into the "Serious icing-glide power" category.
A pilot flying a Cessna 152 that landed at Birchwood about 15 minutes after the accident reported that while on approach, his airplane's engine developed carburetor ice requiring the use of carburetor heat.
Post-Accident Examination
On April 30, the NTSB investigator-in-charge and an FAA airworthiness inspector examined the wreckage. No preaccident mechanical anomalies were discovered. Both engine magnetos were removed and bench-tested on May 1 at Alaskan Aircraft Engines; they produced spark at all terminals.
Additional Information
The Piper PA-24-180 Pilot Operating Handbook's approach and landing section states that carburetor heat should not be applied unless there is indication of carburetor icing, as its use causes a loss of engine power that may be critical during a go-around and can induce detonation. The FAA's Advisory Circular 61-23C notes that carburetor ice is likely at temperatures between 20°F and 70°F with visible moisture or high humidity, and engines are particularly susceptible during low or closed throttle settings. Advisory Circular 20-113 states that vaporization icing may occur at temperatures from 32°F to 100°F with relative humidity of 50% or above; when the temperature/dew point spread is 20° or less, relative humidity is 50% or higher, indicating potential icing conditions.
The instructor noted that the accident might have been avoided if the simulated engine failure had been initiated closer to the airport or concluded at a higher altitude, allowing more time for an engine restart.