N7352PPiper PA-24-180 · 1961

On April 28, 2009, about 1500 Alaska daylight time, a Piper PA-24-180 airplane, N7352P, sustained substantial damage during a forced landing following a reported loss of engine power while on approach to the Birchwood Airport, Chugiak, Alaska. The certificated flight instructor and the private pilot were not injured. The airplane was being operated as a visual flight rules (VFR) instructional flight under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91, when the accident occurred. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The flight originated at the Merrill Field Airport, Anchorage, Alaska, about 1450.

During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on April 28, the flight instructor reported that he was in the right seat, and the private pilot/airplane owner was in the left seat. The instructor said that the purpose of the flight was to administer a biennial flight review to the pilot, whose previous flight review had expired.

The instructor said that after departing the Merrill Field Airport, they flew north at 1,600 feet msl. He said that as the airplane approached the Birchwood Airport, he closed the engine throttle, and told the pilot that he was simulating an engine failure, then he told the pilot to demonstrate an emergency descent and landing at the Birchwood Airport. The instructor noted that the pilot followed the emergency procedures for a loss of engine power, and immediately entered a right base for landing on Runway 1L.

The instructor reported that as the pilot continued the simulated emergency descent, and as the airplane turned from a right base leg to final approach, he momentarily advanced the engine throttle to ensure engine power was still available, and the engine appeared to respond accordingly. The instructor said that while on short final for Runway 1L, the pilot lowered the landing gear, and the airplane's descent rate increased significantly. The instructor then commanded the pilot to go-around when he felt the airplane was too low on the approach, and the pilot immediately applied full engine throttle, but the engine did not respond. The instructor confirmed that the throttle was full open, and the pilot then pulled aft on the control yoke to cushion the landing on the grass-covered terrain. The instructor said that during the forced landing the airplane struck a perimeter fence, then slid for several feet on the grass-covered terrain. The nose and main landing gear collapsed, and the airplane sustained substantial damage to the fuselage and wings.

The airplane was equipped with a carburetor-equipped Lycoming O-360-A1A engine.

Both the instructor and pilot reported that carburetor heat was not used during the simulated emergency descent and approach.

The Piper PA-24-180 Pilot Operating Handbook (POH), engine and propeller descriptions section, approach and landing, states, in part: "Carburetor heat should not be applied unless there is indication of carburetor icing, since the use of carburetor heat causes a loss in engine power which may be critical in the event of a go-around, and can induce detonation in this situation."

During a telephone conversation with the NTSB IIC on May 1, a pilot that was flying a Cessna 152, which landed at the Birchwood Airport about 15 minutes after the accident, reported that while on approach, his airplane's engine developed carburetor ice, which required the use of carburetor heat.

The closest official weather observation station is located at the Birchwood Airport. At 1453, an Aviation Routine Weather Report (METAR) was reporting, in part: Wind, 310 degrees (true) at 5 knots; visibility, 10 statute miles; clouds and sky condition, clear; temperature, 54 degrees F; dew point, 32 degrees F; altimeter, 30.39 inHg. The Birchwood Airport is situated adjacent to the ocean waters of the Cook Inlet.

The temperature and dew point were entered into a carburetor icing probability chart, which coincided with the "Serious icing-glide power" category.

In his written report to the NTSB the instructor noted that the accident might have been avoided if he had initiated the simulated engine failure closer to the airport, or concluded the simulation at a higher altitude, resulting in more time to attempt an engine restart.

The NTSB IIC, and a Federal Aviation Administration (FAA) airworthiness inspector from the Anchorage Flight Standards District Office (FSDO), went to the accident site on April 30 and examined the wreckage. No preaccident mechanical anomalies were discovered during the examination. Both engine magnetos were removed for bench testing.

On May 1, under the direction of the NTSB IIC, the undamaged magnetos were placed on a test bench at Alaskan Aircraft Engines, Anchorage. Both magnetos produced spark at all terminals.

The FAA's Advisory Circular (AC) 61-23C, Pilot's Handbook of Aeronautical Knowledge, Chapter 2, Carburetor Icing, states, in part: "... if the temperature is between -7 degrees C (20 degrees F) and 21 degrees C (70 degrees F), with visible moisture or high humidity, the pilot should be constantly on the alert for carburetor ice. During low or closed throttle setting, an engine is particularly susceptible to carburetor icing.”

The FAA's AC 20-113, Pilot Precautions and Procedures to be taken in Preventing Aircraft Reciprocating Engine Induction System and Fuel System Icing Problems, states, in part: "Vaporization icing may occur at temperatures from 32 degrees F to as high as 100 degrees F with a relative humidity of 50 percent or above... Since aviation weather reports normally include air temperature and dew point temperature, it is possible to relate the temperature/dew point spread to relative humidity. As the spread becomes less, relative humidity increases and becomes 100 percent when temperature and dew point are the same. In general, when the temperature/dew point spread reaches 20 degrees or less, you have a relative humidity of 50 percent or higher and are in potential icing conditions."