N3675PPiper PA-18-150 · 1955

On August 6, 2015, about 2350 Alaska daylight time, a tailwheel-equipped Piper PA-18-150 airplane, N3675P, presumably sustained substantial damage during impact with the ocean waters of Knik Arm, about 4 miles northwest of Chugiak, Alaska. The private pilot and sole passenger were fatally injured. The airplane was registered to, and operated by, the pilot as a visual flight rules (VFR) cross-country personal flight under the provisions of Title 14 Code of Federal Regulations (CFR) Part 91, when the accident occurred. Visual meteorological conditions (VMC) prevailed along the route of flight, and no flight plan was filed. The flight departed the McGrath Airport, McGrath, Alaska, at 2111, en route to the Birchwood Airport, Chugiak.

According to family members, the pilot resided in McGrath, and the purpose of the flight was to attend a family function scheduled for the following day in Anchorage.

A distress call was received by the Alaska State Troopers at 2354 from the pilot stating that he had just crashed his airplane in the waters of the Knik Arm, it was too far to swim, and he was requesting immediate rescue.

At 0003, the 11th Air Force's Rescue Coordination Center received notification of the accident and immediately diverted two C-17 Globemaster airplanes from a training mission to begin searching for the airplane and occupants. The two airplanes were on-scene and searching the waters of Knik Arm by 0016.

Search personnel from the Alaska State Troopers, Civil Air Patrol, and U.S. Coast Guard along with several volunteers aided in the search effort.

On August 7, about 0610, the Alaska Air National Guard located the wreckage about 1.8 miles northwest of the Birchwood Airport. The airplane was inverted and mostly submerged under the salt water with the bottom of the fuselage, wing strut attach points, landing gear, and a portion of the propeller protruding above the water. No survivors were found inside or in the vicinity of the wreckage.

The pilot, age 29, held a private pilot certificate with an airplane single engine land rating. His most recent third-class medical certificate was issued on June 13, 2015, with no limitations.

No personal logbooks were located for the pilot. According to family members, he had accumulated about 360 total flight hours in airplanes, and had recently completed an emergency maneuvers training course.

The airplane was a Piper PA18-150, manufactured in 1955 and equipped with a Lycoming O-320 series engine. The tachometer at the time of the accident displayed 995.08 hours. At the time of the last annual inspection, completed on January 16, 2015, the tachometer read 897.58 hours and the total time in service was 4473.58 hours.

The closest weather reporting facility is Birchwood Airport, Chugiak, about 2 miles southeast of the accident site. At 2336, an aviation routine weather report (METAR) from the Birchwood Airport reported, in part: wind from 120 degrees at 3 knots; sky condition, clear; visibility 10 statute miles; temperature 63 degrees F; dew point 52 degrees F; altimeter 29.85 inHg.

The airplane was a Piper PA18-150, manufactured in 1955 and equipped with a Lycoming O-320 series engine. The tachometer at the time of the accident displayed 995.08 hours. At the time of the last annual inspection, completed on January 16, 2015, the tachometer read 897.58 hours and the total time in service was 4473.58 hours.

On August 8, 2015, under the supervision of the NTSB IIC recovery crews recovered the wreckage from the ocean floor and transported it to Birchwood Airport.

The airplane's wreckage was subject to several tide cycles, which partially filled the wreckage with organic material adding additional weight. During the extraction the airframe could not support the additional weight.

Both wings fractured at the forward spar attach points and folded aft. The fuselage fractured about 3 feet forward of the horizontal stabilizer and remained attached by the rudder and elevator control cables. The carburetor heat control was found in the "off" or "cold" position.

The engine remained attached to the airframe by the engine mount. Visual examination of the engine revealed no evidence of pre-impact catastrophic mechanical malfunction or fire. Both propeller blades remained attached to the engine crankshaft. There was no conclusive evidence observed on the propeller blades consistent with the absorption of rotational energy sustained at the time of impact.

All the primary flight control surfaces remained connected to their respective attach points, and flight control continuity was verified from all of the primary flight control surfaces to the cockpit.

The wreckage was relocated to Alaska Claims Service's, Wasilla, Alaska. On August 13, 2015, a wreckage examination and layout was performed under the direction of the NTSB IIC. Another NTSB investigator, two FAA aviation safety inspectors, and an air safety investigator from Piper Aircraft and Lycoming Engines assisted the NTSB IIC.

The fuel selector valve was found in an intermediate position between the right fuel tank and the off position. It could not be determined if the selector valve was in this position prior to the impact sequence or as a result of the occupant's evacuation.

The trim jackscrew was measured and determined to be in a slight nose down trim setting.

The left and right wing fuel tanks, gascolator bowl, and carburetor bowl were drained and found to contain a fluid consistent with a combination of salt water and fuel. All samples emitted an odor consistent with automotive gasoline.

The examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.

A Garmin 196 handheld GPS was still mounted on the instrument panel and all cables were still attached when the airplane was extricated from the water. The unit sent to the NTSB Vehicle Recorders Laboratory in Washington, D.C. for examination.

A NTSB electrical engineer was able to extract the GPS data for the accident flight, which included, in part, time, latitude, longitude, and GPS altitude. Groundspeed and course information were derived from the extracted parameters.

At 2340 AKD [07:40:50 Coordinated Universal Time (UTC)], the airplane began a climb from 1156 feet above mean sea level (msl). At 2345, the airplane achieved a peak recorded altitude of 1549 feet msl and began an immediate descent. Over the next 2:08, the airplane descended 317 feet, averaging about 176 feet per minute. During the climb and descent, the airspeed of the airplane remained within about 5 knots.

At 2347, the rate of descent began to steadily increase to a peak vertical velocity of about 947 feet per minute and averaged about 890 feet per minute until the last data point at 2349 when the airplane was 29 feet msl. During the final 1:17 of recorded data, the heading of the airplane changed from an east-southeast heading to a south-southeasterly heading toward the nearest point of land.

A flight track map overlay, and tabular data corresponding to the accident flight are available in the public docket for this accident.

When the temperature and dew point are entered into a carburetor icing probability chart, the result is in the "moderate icing – cruise power or serious icing – glide power" category.

A postaccident review of archived Federal Aviation Administration (FAA) radio communication recordings revealed that at 2109, the pilot reported taxiing for departure from the McGrath Airport. At 2111, he reporting taking off from runway 16 at the McGrath Airport. No further radio communications were received from the airplane.

To date, the remains of the pilot have not been located, therefore, no pathological or toxicology information exists. At the time of his last medical examination, no concerns were reported by the airman and no significant issues were identified by the Aviation Medical Examiner.

On August 29, the remains of the passenger were located and recovered from the shore of the Cook Inlet. A postmortem examination conducted by the Alaska State Medical Examiner's Office attributed the cause of death to be drowning. No lifejacket or other personal flotation device was found with the passenger.

The FAA Civil Aeromedical Institute did not perform toxicology examinations for the passenger.

At 2354, a distress call was received by the Alaska State Troopers from the pilot, stating that he had just crashed in the waters of Knik Arm, and was standing on top of his airplane. He requested rescue and stated that he was too far from shore to swim. At 0003, the Alaska Rescue Coordination Center received notification of the accident and air assets were on scene searching at 0016, but due to the rising tide, did not locate the airplane until about 0610 on August 7. When the wreckage was recovered from the water, no occupants were present inside.

The area the airplane was located in was a portion of the Knik Arm consisting of fast moving salt water. Several glacier fed rivers terminate at the inlet and visibility in the water is often less than 1 foot due to turbidity. The Inlet is an area with strong tidal influence, and strong currents.

On August 6, at 2354, a buoy located near the Port of Anchorage recorded the water temperature at 61.3 degrees Fahrenheit.

A February 2008 NATO Research and Technology Organization publication titled Survival at Sea for Mariners, Aviators and Search and Rescue Personnel described the four stages of cold water immersion as:

• Stage 1: Initial immersion responses or cold shock (3-5 min.)

• Stage 2: Short-term immersion or swimming failure (5-30 min.)

• Stage 3: Hypothermia (= 30 min.)

• Stage 4: Post-rescue collapse or circum rescue collapse

In this publication, it is stated that during stage 1, "death from cold shock is not uncommon," and it takes place "within 3-5 minutes of immersion." It further states that swimming in "cold, dense water" is very dangerous (stage 2). As the body becomes exhausted, the person transitions to a more vertical position before total submersion.

A US Coast Guard article from January 6, 2015, titled A Lifejacket Buys You Time, defines "cold" as water temperature less than 70 degrees. It further states that it takes at least an hour for the full effects of hypothermia to set in and another hour after loss of consciousness for the heart to stop. It further states that without a lifejacket or other flotation device, drowning will occur prior to death from hypothermia.

The airplane was equipped with an ACK Technologies, Inc., E-04 406MHz emergency locator transmitter (ELT). The ELT is designed to transmit a signal on 406MHz, 243MHz and 121.5MHz frequencies. The Alaska Rescue Coordination Center (AKRCC) reported never receiving a 406MHz signal. Currently, ELT's are not certified, nor required to be certified, for operation during or after submersion.

Engine

On August 13, 2015, an engine examination was performed by Lycoming Engines, under the supervision of the NTSB IIC. No anomalies, contamination or evidence of malfunction was found in any of the engine accessories. The cylinders, pistons, valve train, crankshaft and other internal components were all without evidence of anomaly or malfunction with the exception of the shared camshaft lobe for the number 3 and 4 cylinders. A lighted borescope was used to visualize the subject camlobe. The camshaft lobe was worn at the "lifting" area of the lobe, but an actual measurement of wear could not be ascertained. There was clear burnished camlobe edges and spalled surface visible on the tappet face.