NTSB Factual Report

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 weight of 1141.1, plus the empty belly tank weight of 30 pounds, plus 432 pounds of fuel (72 gallons times 6 pounds per gallon), plus the pilot and passenger weighing 420 pounds and 60 pounds of survival and personal equipment, required the airplane to weigh at least 2083 pounds at take off from Anchorage and at least 1977 pounds upon arrival at the accident location. No determination could be made as to the exact weight of the aircraft at the time of the accident.

A calculation of the Arctic Tern's useful load was performed by applying the weight of the factory belly tank installation, the weight of the accident pilot and guide partner, and 60 pounds of survival, personal gear and food. Based upon this data, the Arctic Tern airplane would have exceeded the maximum certificated weight before any fuel was added to its wing or belly tanks.

No flight tests to determine stall speeds, spin characteristics or recovery, climb or cruise speeds, or center-of-gravity numerical data have been recorded on the Arctic Tern S1B2 at weights above 1650 pounds. A calculation using the Arctic Tern's production weight record indicates that the airplane would be limited to a maximum of 11.5 gallons of fuel in the belly tank if flown by a 170 pound pilot (standard weight used by FAA calculations), with full wing tanks. (20 gallons left and right) Given the accident pilot's weight alone, he would always have exceeded the certificated gross weight of the aircraft whenever any fuel exceeding 4.8 gallons was carried in the belly tank in addition to full wing fuel. The aircraft, configured with an FAA-Approved, factory-installed belly tank and filled to the capacity of those tanks, can not remain within the certificated weights if flown by a pilot weighing greater than forty seven (47) pounds. No caution or warning is given that the full tank capacity of the airplane can ever be used for flight.

The S1B2 FAA-Approved Flight Manual provides the following caution on page 9 regarding the use of the belly tank:

"The maximum approved capacity of the belly tank is 32 U.S. gallons. However, when both main tanks are full (20 U.S. gallons each), the amount of fuel carried in the belly tank must be reduced so as not to exceed the maximum approved gross weight (1650 lbs.) of the airplane. Since it is the responsibility of the pilot to assure that the aircraft is loaded within its approved weight and center of gravity limits, the amount of fuel which may be carried in the auxiliary belly tank must be calculated prior to each flight."

The Safety Board was provided with the FAA Approved Airplane Flight Manual for the Arctic Tern S-1B2, serial number 1010, N59AT. In the information provide as Flight Procedures, certain pilot alerts are indicated. The instructions in "Approach to a landing stall" include "*REMEMBER*: Right Rudder!". Instructions to "Takeoff and Departure Stall:" include the same statement, "REMEMBER*: Right Rudder." The procedures for an "Accelerated Maneuver Stall" also state: "*REMEMBER*: Opposite Aeleron [sic]" The flight manual does not stipulate the reason for the need to use opposite aileron or rudder.

METEOROLOGICAL INFORMATION

The National Weather Service (NWS) reports, forecasts and observation for the Gulkana area and the Copper River Basin for July 31, 1993, indicated that visual meteorological conditions existed in an area dominated by a weakening high pressure area. Forecasts for the route of flight and area of the accident were provided to the pilot by Kenai Flight Service Station (FSS) and indicated that conditions of 5000 foot to 7000 foot scattered clouds, variable to broken clouds, varying to 10,000 to 12,000 foot scattered to broken clouds with visibility at Gulkana given at 25 miles. No AIRMETS (airmen's meteorological reports) for icing or turbulence were in effect. The freezing level was given as 10,000 to 11,000 feet and the wind measured at Gulkana was from the southwest at five knots.

COMMUNICATIONS

The last known communications from the airplane were with Kenai FSS between 0613 and 0627 ADT on July 31, 1993. No records of landing or refueling are known to investigators.

WRECKAGE AND IMPACT INFORMATION

Still photographs and video record of the accident scene, as well as sketches and interview of the Alaska State Trooper rescue team leader provided documentation of the impact site.

All major structural components of the airplane were identified and located at the principal location. There was no evidence of inflight separation.

The left wing spar (wood construction) was shattered into pieces from the left tip to approximately four feet from the outboard end and were distributed in a line. The fabric covering of the left wing was unburned from the tip inboard to the area of the upper lift strut(s) attachment point. Four of the five metal disk inspection plates on the lower surface had been displaced toward the left wing tip. One metal disk was missing. The left wingtips show jagged shattering and tearing to approximately two feet, followed by compression ripples in the wing structure parallel to the leading edge outboard tip. Both front and back left wing lift struts show a rearward buckling.

The engine was displaced on its mounts at the firewall approximately 90 degrees to the right. No propeller was found, however photographs of the propeller mounting flange indicated complete shearing of the propeller mounting bolts.

Both wing lift strut assemblies remained attached to the fuselage frame at the bottom and the wing structure at the top. Both wing structures were bent aft of perpendicular, the left wing found aft to 40 degrees beyond perpendicular and the right wing structure aft of perpendicular by 20 degrees.

All fabric and non-ferrous metal in the cabin and cockpit had been consumed or melted in the fire. While pieces of wing spar wood were distributed downslope for a distance of 15 feet and were unburned, investigators on-scene photographed ground scorching upslope beyond the wreckage frame, but not downslope. The fuselage was found resting inverted with the cockpit below. While the shell (glass fibers) of the belly tank remained, the forward end of the belly tank over the cockpit area was missing. It was not possible to determine whether the forward end of the belly tank had ruptured due to impact or had been burned away in the post crash fire. The clasped seat belt harness buckles were found in front of the occupants. The on-scene investigators were unable to determine if the aircraft was equipped with dual controls.

ADDITIONAL INFORMATION

Information available to investigators indicates that the wreckage remains at the accident site.

NTSB Probable Cause

THE PILOT'S ATTEMPTED FLIGHT IN AN AIRPLANE WHICH EXCEEDED THE MAXIMUM ALLOWABLE WEIGHT. THE HIGH MOUNTAINOUS TERRAIN WAS A FACTOR.