ANC93FA054
ANC93FA054

HISTORY OF FLIGHT

On April 23, 1993, at approximately 1730 Alaska daylight time, a tundra tire wheel equipped Piper PA-18 airplane, N3741Z, collided with the terrain approximately 20 miles north of Palmer, Alaska. The private pilot and one passenger, both who were registered Alaska big game guides, were fatally injured, and the airplane was substantially damaged by impact forces. The local flight, conducted for business purposes, operating under 14 CFR Part 91, departed Merrill Field, Anchorage, Alaska at approximately 1510. Visual meteorological conditions (VMC) existed, and no flight plan was filed.

The wreckage was located by an Air National Guard rescue helicopter at approximately the 5000 foot level of a bowl, open to the south and surrounded by a mountain rim rising to approximately 7000 feet. The tundra tire equipped PA 18 Supercub airplane was found to have impacted in a nearly vertical angle. There was no evidence of a pre-impact or post impact fire.

Weather conditions in the area of the accident at the time were reported to be visual meteorological conditions (VMC) with winds less than 8 knots and unlimited visibility. Initial notification to the USAF Rescue Coordination Center (RCC) came via the Search and Rescue Satellite System (SARSAT) which was alerted to the airplane's emergency locator transmitter (ELT) at 1730 ADT. Alaska Air National Guard rescue helicopter located the crash site at approximately 1745 on April 23, 1993, and reported a single deceased pilot was found. The crash site was reached by Alaska State Troopers on April 24, 1993, who confirmed two fatalities and removed the deceased. The NTSB investigation was conducted on scene on April 25, 1993.

Information provided to the NTSB indicated that the two guides were "looking at areas to hunt for the fall hunt, as they had clients lined up." Investigators at the scene observed dall sheep and mountain goats in the area. Both individuals were Board Certified big game guides in the State of Alaska. The guide in the rear seat was also a certificated commercial pilot.

In an interview with the father of the pilot, the NTSB was told that Mr. Finch "flew over the house, going to Kashwitna about 3:30 (1530 Alaska standard time)." The pilot's father said also that he had been talking to prospective clients and had lined up a number of hunts. Mr. Finch (senior) lived in Eagle River, Alaska, approximately 10 miles from the Merrill Field departure airport, and en route to Kashwitna.

INJURIES TO PERSONS

The two occupants of N3741Z received fatal injuries.

DAMAGE TO AIRCRAFT

The airplane was substantially damaged, with only the vertical and horizontal stabilizer sustaining minor damage. The remainder of the airplane was extensively bent, twisted and broken. Refer to the "WRECKAGE AND IMPACT INFORMATION and photographic evidence attached. There was no evidence of pre-impact or post-impact fire.

PERSONNEL INFORMATION

Bradley A. Finch

The pilot in command, Bradley A. Finch of Eagle River, Alaska, purchased Piper PA-18-150, N3741Z, on January 27, 1993. He entered flight training at SUNAIR Aviation Center, 15115 Airport Drive, Scottsdale, Arizona, on January 28, 1993. Although SUNAIR conducts classes under 14 CFR Part 141, the flight school told the NTSB that the student pilot had arrived with evidence that he had passed the FAA written examination for a private pilot's certificate and had said that he had attended a ground school in Alaska and preferred to do a majority of studying at home. Training for Mr. Finch was conducted under 14 CFR Part 61.

Mr. Finch was issued a student pilot's certificate on February 12, 1993, and his temporary private pilot's certificate on March 25, 1993. He logged a total of 49 dual instructional hours and 25 solo hours while in training. The aircraft used for training was the Citabria 7GCAA, although 3 flights were conducted in a Cessna 172 and one flight was in a PA-18-150 Supercub.

Records found on scene indicated that the private pilot had obtained his pilot's certificate on March 25, 1993, having logged approximately 74 hours in a Citabria 7GCAA during a period of training in Arizona between January and March 1993. He had logged 4.3 hours flight time in the accident airplane, in solo transition to the PA-18 Supercub (log book records indicate self-taught training) in two flights following his return to Alaska. The accident flight was the pilot's third flight in the PA-18 in Alaska. His total pilot experience at the time of the accident was logged as 78.6 hours.

Two previous flights in the PA-18 Supercub were logged in the pilot's personal log book to have occurred on April 17, and April 20, 1993 for a duration of 3.0 and 1.3 hours, respectively. The pilot's log listed the flight time as all "pilot in command," originating and ending the flight at Merrill Field, in Anchorage, Alaska. At the conclusion of the April 20 flight, the pilot totalled his "pilot in command" time as 25.2 hours.

His logbook indicates that he had 48 minutes (0.8 hours) of training in a PA-18-150 Supercub on March 8, 1993. The flight instructor on that flight told the NTSB that the particular PA-18 used in training was not equipped with oversized (tundra) tires and that he told Mr. Finch that he needed additional training in Supercubs before engaging in any "bush" flying in Alaska, and would be able to schedule him for training to show him the characteristics of that particular airplane. This instructor said that Mr. Finch told him that he "was a big game guide, and that lot's of his friends were anxious to get him into bush flying."

Mr. Finch left SUNAIR after receiving his private pilot's certificate. He reportedly told his instructor that he "didn't plan to start flying clients until he'd flown 'in the bush' for at least a year."

Thomas Kent Besh

The passenger in the rear seat of the accident aircraft, Mr. Thomas K. Besh, was also a guide certified by the Alaska Big Game Board. He also held a commercial pilot's certificate, with ratings in airplanes; single engine land and single engine sea.

FAA records indicated that Mr. Besh had certificate limitations to carrying passengers in airplanes on cross-country flights of 50 nautical miles or less. Records provided to the FAA indicated that he had 900 flight hours of pilot experience.

Mr. Finch's log book of the two previous PA-18 flights in the accident airplane did not indicate that Mr. Besh or any other person was on board during those flights. Mr. Finch's log book indicated that he was the "pilot in command" and did not indicate that any instruction was given or received during those flights.

AIRCRAFT INFORMATION

The Piper PA-18-150, N3741Z, Serial Number 7497, was a high wing, single engine, conventional wheeled land plane. It had tandem seating for two occupants. It was powered by a Lycoming 0-320 reciprocating, normally aspirated, 4 cylinder engine of 150 horse power. The certified maximum gross weight was 1750 pounds. Investigators calculated the approximate weight of the airplane, fuel and occupants to be below maximum gross weight.

The accident airplane was equipped with "Airstreak" balloon tires approximately 30 inches in diameter, 30 X 13.0 - 6. No FAA approval, field or Supplemental Type Certificate (STC) or change to the accident airplane's flight manual was found by investigators.

The NTSB asked the FAA Small Airplane Directorate, Anchorage Aircraft Certification Office, to provide data on the effect of large tires upon the stalling speed of the Piper PA-18-150 Supercub airplane. That office stated, in part:

"We have no data on the effect on large tires upon the stalling speed of the Piper PA-18 "150" airplane. We do have data on the reduction in the rate of climb and the reduction in cruising speed and range produced by installing one type of large wheel and tire arrangement: the Schneider 28 inch (Bushmaster Management Company) Model SWS-11000-C wheel and tire combinations approved was found to reduce the rate of climb of the PA-18 "150" airplane by approximately 100 feet per minute and to reduce the airplane's cruising speed by approximately 8% (percent). The performance reductions requires an Airplane Flight Manual Supplement, and one was approved for STC SA2338NM. We are transmitting relevant pages from the SWS-11000-C project file herewith. Note that large and heavy tires and wheels are expected to increase stall speed, reduce rate of climb, reduce cruising speed and range, limit maximum safe dive speed, and adversely affect airframe vibration characteristics. They may also cause difficulty in taking off, landing, ground handling and braking. If N3741Z, the April 24th accident airplane, was equipped with 'Airstreak' 30 x 13.0 - 6 tundra tires, we ask that you confirm this fact by return communication. No approved data exist regarding any of the changes in limitations or performance these particular tires may produce. If they reduced the airplane's rate of climb or increase its stalling speed they may have contributed to the accident and mandatory corrective action by the FAA may be advisable." (copy of communication as attachment)

The NTSB confirmed to the FAA Anchorage Aircraft Certification Office that investigators found the accident airplane to have been equipped with "Airstreak" 30 x 13.0 - 6 tundra tires (see photos attached).

The NTSB also requested of the FAA Anchorage Aircraft Certification Office, any flight test data conducted on a PA-18 Supercub airplane, with any large "tundra" tire, which would provide aerodynamic performance data which could be used to calculate changes in stall speed or stall angle of attack for that aircraft, for which large tire STC's or field approvals were given. The FAA told investigators that "the STC's were issued a while back, there is no flight data."

METEOROLOGICAL INFORMATION

There were no known witnesses to the aircraft accident and to the weather on scene at the 5000 foot level in the Kashwitna drainage. FAA Flight Service provided information that the Palmer, Alaska, (PAQ) at 1800 Alaska standard time, was recording scattered to broken sky conditions at 18,000 feet, 40 miles visibility, a temperature of 59 degrees (F) and a dewpoint of 27 degrees (F), wind from the south (180 degrees magnetic) at 10 knots and an altimeter of 29.76 inches of mercury (Hg"). The National Weather Service indicated that the area conditions were dominated by a high pressure system and a wide area of visual flight rule (VFR) conditions prevailed.

WRECKAGE AND IMPACT INFORMATION

The aircraft was found in a nearly vertical position in compact snow, with the forward fuselage penetrating the snow to a depth of approximately 5 feet, or about the level of the pilot's seat. The spinner was dented and one propeller blade was bent aft 9 inches from the propeller arc plane, and twisted to approximately 20 degrees angle of attack from the root to the mid point where the aft bending began. The other blade was bent aft 2 inches from the arc plane and twisted to nearly zero angle of attack.

Aft of the propeller spinner, the cogs on the propeller gear which mates with the starter, matched jagged sawtooth marks on the crushed cowl. These jagged sawtooth marks were found to be nearly aligned with the aircraft axis on one edge and the cut angled more or less 90 degrees to the side. (see photographic attachments)

The cowl was bent, ripped and twisted and the engine mounts had been bent and broken downward, with the engine resting approximately 25 degrees downward from normal alignment. The cockpit and cabin was crushed and twisted and the instrument panel had been crushed in and deformed. The glass faces of instruments were broken, except for the wet compass, the Radio Magnetic Indicator (RMI) and the clock. The altimeter face was broken and the altimeter indicator (2 needle) stopped at 5,150 feet with a Kohlsman window setting as 30.09 inches of mercury (HG").

The fuselage was broken and bent upward aft of the cabin and rested at approximately a 35 degree angle to normal alignment. The tundra-tire equipped (30 inch Airstreaks) remained attached to broken gear struts. The bungee connections were intact.

The vertical and horizontal stabilizer received minor damage and the 8" tailwheel appeared undamaged.

Both wings were crushed aft from the leading edge to an approximate depth of 6 inches, though the forward spar was generally undamaged. The wings were broken aft from the wing roots to a rearward sweep of approximately 5 degrees. Flaps were found to be retracted. Flight control continuity could not be completely established due to extensive crushing of the cockpit, however, cable and pulleys were intact in the wing to the broken roots, as well as in and from the empennage through the fuselage. No failures were noted in the flight control cables or attaching hardware. The aircraft tubing structure, control cables, hardware and other metal showed no evidence of rust or corrosion.

The aircraft skin fabric was examined and appeared sound and strong where not ripped from the impact damage.

Neither wing showed tip strike damage.

Empennage support wires remained attached. Wing lift struts appeared to be attached at impact, however there was evidence that the right wing lift strut had been cut and bent outward during the rescue phase of the accident aftermath.

Seat backs were both bent forward. Both seats had lap belts attached, however, shoulder harnesses were not installed. The airplane had a control stick in the both the front and back positions. The cockpit space appeared to have retained its approximate original spatial dimensions, although forward firewall area showed a crushing intrusion near the pilot's foot pedals to nearly six inches.

An ELT was installed and was instrumental in the location of the crash site.

ADDITIONAL DATA/INFORMATION

The NTSB IIC released the wreckage to Louis H. Finch on May 9, 1993. Mr. Finch said that he was a metal worker. He told the NTSB that he had inspected the cables in the wreckage and found them to be "attached." The wreckage was reportedly recovered by commercial helicopter. The helicopter pilot told the NTSB that parts of the wreckage "had been dropped" and recovered during the process.

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