ANC93LA143

Both occupants were certified Alaska guides. On-scene evidence showed that the airplane impacted mountainous terrain at a steep angle while rotating to the left. The airplane had an faa-approved factory auxiliary 32-GAL belly fuel tank installed; no weight & balance revision was found in the airplane's records. Airplane's weight at time of accident over 20% greater than max allowable. No flight test/performance data available for airplane with aux tank installed. In addition, the airplane was equipped with tundra tires; no STC was recorded, nor was certification flight test ever conducted to determine CG envelope with tundra tires installed. Airplane recovered 8/12/93.

History of flight

On or after July 31, 1993, at an unknown time, an Interstate S- 1B2 Arctic Tern airplane, N59AT, impacted in mountainous and glacial terrain, approximately 21 miles north of Paxton, Alaska. The airplane was being operated for business purposes by the owners of Pinnacle Guide Service, under 14 CFR Part 91, on a VFR flight plan from Anchorage to Paxton, filed near Anchorage on July 31, 1993, at 0619, Alaska daylight time. The airplane was declared overdue on that day and located by Search and Rescue (SAR) aircraft at approximately 1530 on August 12, 1993. Visual meteorological conditions existed on the route of flight along the Glenn Highway from Anchorage to Gulkana and along the Richardson Highway to Paxton on July 31, 1993. The private pilot and his passenger were reported to be certified Alaska big game guides. Both received fatal injuries and the airplane was destroyed by fire.

The pilot in command, Bert A. Flotre, filed a VFR flight plan with Kenai Radio (via Anchorage remote transceiver site) at 0619 ADT stating that he and a passenger had departed Anchorage "ten minutes ago" and that he was going to Paxton and would close (the VFR flight plan) with (terminate by communicating with) Gulkana. The pilot stated that he had eight hours of fuel on board.

On August 12, 1993, Sgt. Steve Heckman, Alaska State Trooper, (AST) reached the site of the wreckage. Sergeant Heckman determined that due to the high altitude and the steep, (50 degrees) loose terrain surface, the on scene investigation and recovery of the deceased would be hazardous. Attempts to make positive identification and examine the scene were aborted on August 12 due to safety considerations and the need for specialized mountain equipment. Efforts to return to the scene were delayed by weather and high winds. Upon the recommendation of the AST, the NTSB decided that the on-scene investigation could be completed with prior coordination between a Safety Board Air Safety Investigator and the AST climbing team. On August 17, 1993, a specially equipped climbing team of Alaska State Troopers, headed by Heckman, reached the scene and conducted an investigation and recovered the remains of the deceased. The AST investigation and communication with the NTSB included complete descriptions, photographs and video recordings of the scene.

Injuries to persons

The pilot in command, Mr. Flotre, and the passenger in the rear seat of the Arctic Tern, Mr. Steven K. Smith of Anchorage, Alaska, received fatal injuries. A pathologist report on the pilot listed the final diagnosis as extensive fourth degree burns. The report also indicated that no soot was found in the trachea of the deceased. The blood toxicological examination was reported to be negative for licit and illicit drugs and their metabolites.

Damage to aircraft

The aircraft was destroyed. See wreckage and impact information.

Other damage

There was no environmental damage reported. A post-crash fire consumed most of the materials of the aircraft. Information received by the NTSB indicated that the tubular frame remained at the accident location.

Personnel information

Records provided to the NTSB indicated that the private pilot flew his first solo flight on November 18, 1989. At the time of the accident he had an FAA Third Class medical certificate, dated August 1992. Records were not available to determine the pilot's total flight hours or experience in the make and model of airplane.

Mr. Flotre was a certified Alaska Guide-Outfitter, number R723. On an Alaska Big Game Board application filed in January 1991, he listed his height and weight as 6'1" and 210 pounds. His date of birth was May 30, 1962. Records obtained from the Big Game Board in Juneau did not indicate, nor were they required to, that Mr. Flotre had a pilot's license or flight experience.

Mr. Steven K. Smith, the passenger in the back seat of the accident airplane was also an Alaska Guide-Outfitter, number R665. His date of birth was June 10, 1962. The State of Alaska, Department of Public Safety records indicated that Mr. Smith's height and weight was given as 6'0" and 210 pounds on his most recent drivers license. Records obtained from the Big Game Board in Juneau did not indicate, nor were they required to, that Mr. Smith had a pilot's license or flight experience.

Aircraft information

The aircraft was manufactured in Alaska by Arctic Aircraft Company, as serial number 1010, in August of 1978 and received an FAA approving test flight on September 6, 1978. As manufactured, and as operated by the pilot at the time, the aircraft was equipped with a Lycoming 160 HP engine, model O-320-B2B.

Records indicate that the airplane was purchased by Mr. Flotre on November 18, 1989. An annual inspection of the engine and airframe was completed on January 13, 1993. At that time, the FAA certified mechanic indicated that the aircraft was equipped with skis for winter operation. No records were found that indicated that the skis were replaced with wheels. Witness stated that the airplane was equipped with "tundra tires" at the time it departed on the accident flight.

An FAA Form 337, (Major Repair and Alteration) indicated that 30 inch tires (30X13X6) had been removed and replaced by 24X10X6 inch tires on May 2, 1982. Records indicate that on annual occasions since that time, those tires were replaced with skis. An FAA Form 337, on January 18, 1991, indicated that the type of skis were Landes L3000 wheel replacement skis.

A photograph of N59AT reportedly taken in the spring of 1993 showed the aircraft taxiing and equipped with 24 inch tires. No Supplemental Type Certificate (STC) for those tires was found to be recorded. The FAA Aircraft Certification Office in Anchorage, Alaska, told the NTSB that no certification flight tests have been recorded to determine the center of gravity envelope, the change in stall or other speeds for S12B airplanes equipped with tundra tires. The FAA aerospace engineer Gordon Mandell of the Certification Office told the NTSB that large tires and other modifications such as external belly tanks affect the momentum of airstream over the horizontal stabilizer and ultimately affect the stall characteristics.

The airplane's weight and balance report, completed at the time of manufacture, without the added 32 gallon belly tank and with 850X6 tires and wheels, indicated that the airplane weighed 1149.1 pounds (see Weight & Balance report dated 8/31/78) and had a useful load of 500.9 pounds. The useful load includes fuel, pilot, passenger and cargo.

On March 30, 1990, the aircraft was fitted with an R2B8078 auxiliary belly fuel tank at the Arctic Aircraft Company facility. No weight and balance revision was found in the airplane records for that installation. That tank, according to the FAA-Approved factory installation specification, adds a 32 gallon capacity to the 40 gallon main tank capacity. The weight of the empty belly tank installation, with associated fuel plumbing, is recorded to be 30.1 pounds.

The records of the pilots' weights and the flight plan report of 8 hours of fuel on board at departure from Anchorage, indicates that the aircraft took off with full tanks. A cross-county flight log with fuel consumption records compiled during a previous flight indicated that the aircraft used 8.8 gallons per hour. The aircraft's tank capacity was 72 gallons (including an estimated one gallon of unusable fuel). At a consumption rate of 8.8 gallons per hour, eight hours of flight time would require 70.4 gallons of fuel.

Investigators estimated the weight for personal equipment, survival equipment, clothing, food or overnight supplies to average 60 pounds. With the exception of a plastic mustard container thrown clear of the wreckage, all of the contents of the cabin were consumed in the post crash fire.

The aircraft's empty