By Delon Shurtz - Lethbridge Herald on February 10, 2024.
While an investigation into a fatal plane crash last summer at the Claresholm Industrial Airport has determined that the small Cessna 152 aircraft suddenly lost altitude and spun into the ground, it was unable to determine the cause of the aerodynamic stall and tailspin.
The air transportation investigation report, which is not intended to assign fault or determine liability, rules out a mechanical breakdown and pilot fatigue for the stall and spin, but it was still impossible to determine a specific cause because of the lack of flight path data, the report states.
On Aug. 28, 2023 the pilot took off from the airport for the first time following repairs from a crash a month earlier. Before take-off, however, a fuel leak was noticed near the fuel drain on the right fuel tank. The fuel tanks were filled to troubleshoot the leak, the leak was rectified by maintenance, and the plane was conditionally released for the test flight.
At about 7:30 p.m. the pilot took off and began a shallow climb on the runway track. Several witnesses watched as the plane climbed, but when it had gone only one nautical mile it turned sharply to the left before beginning a steep turning descent.
The plane hit the ground 5,200 feet from the end of the runway, killing the pilot.
Transportation Safety Board investigators did an initial evaluation of the aircraft at the crash site, followed by a more detailed examination after the wreckage was moved to the TSB facility in Edmonton.
“Particular attention was given to those components and systems that could have contributed to a stall/spin scenario; no anomalies were noted,” the report states.
A review of the records of the maintenance performed following a crash a month earlier – the plane ran out of fuel and the pilot was forced to land on a road 26 nautical miles northwest of Lethbridge – indicated that the required work had been completed in accordance with the manufacturer’s maintenance manual.
Maintenance included a leak check of the pitot system, a functional check of the stall warning system, and an independent check of the flight control systems affected by the maintenance activities surrounding the reinstallation of both wings.
A weight-and-balance calculation was performed, and the aircraft weighed 1,543 pounds at takeoff, which is 127 pounds below its maximum gross take-off weight.
“In summary, notwithstanding the extent of the damage, the investigation did not discover anything mechanical that could have led to the aerodynamic stall and spin.”
The investigation also included aircraft performance in relation to the weather conditions, temperature, altitude and fuel/air mixture at the time. The temperature was 29.5C 30 Â minutes before the accident, and 24.5C 30 Â minutes after the accident.
The report points out that air density decreases with increased altitude and temperature, and the combination of high temperature and high elevation can drastically reduce the aerodynamic and engine performance of the airplane. The Claresholm Airport is 3,310 feet above sea level.
The report also indicates that to achieve maximum engine rpm, the mixture control should be leaned anytime operations are conducted above 3,000 feet above sea level.
“The horsepower output of the engine is decreased because its fuel/air mixture is reduced. The propeller develops less thrust because the blades, as airfoils, are less efficient in the thin air. The wings develop less lift because the thin air exerts less force on the airfoils. As a result, the take-off distance is substantially increased, climb performance is substantially reduced and may, in extreme situations, be non-existent.”
Liam MacDonald, media relations co-ordinator with the TSB, said there wasn’t any information available to the investigation to determine whether the pilot had considered the density altitude prior to take-off. He added the TSB “does not resort to speculation where there is no data to support a conclusion/reason for the accident.”
The pilot, who was an aerial photographer for AFS Aerial Photography based in London, Ont., was hired in June of last year and had 256 hours of flight time. According to the investigation report, she had a total flight time of 391 hours at the time of the crash.
The investigation report includes a safety message which reminds pilots to consult their aircraft’s pilot’s operating handbook (POH) for proper setting of the mixture control appropriate for the density altitude to ensure maximum power is available for takeoff and climbout.
“Higher density altitudes result in penalties against take-off distance and climb performance. Pilots are reminded to review the POH when planning a flight in warmer temperatures and at higher airport elevations (high density altitudes) so that they are aware of these penalties.”