History of the Flight
The Alta Flights Limited Cessna 172M (registration C-GRGW, serial number 17265472) departed Springbank Airport, Alberta, at 1642 Mountain Daylight Time on a visual flight rules pipeline patrol to the south. The aircraft had earlier arrived from Edmonton International Airport (CYEG) at 1554, after which the client requested a patrol of a pipeline between Springbank and Pincher Creek.
In the vicinity of the accident site, witnesses observed several low-level left-hand turns. A change in engine sound was heard, followed by entry into a spin to the left and a rapid descent. The aircraft did not recover, and emergency calls were made via satellite phone.
Site Information
The accident occurred approximately 22 nautical miles west-northwest of Claresholm, Alberta, near Chain Lakes Reservoir, at an elevation of 4300 feet above sea level. The aircraft collided with the ground vertically at the south edge of Chaffen Creek, in a nose-down, wings-level attitude on a heading of 260° magnetic. After initial impact, the fuselage bounced and came to rest in the creek. The left wing detached; the right wing remained attached. All four wing fuel tanks separated and contained substantial fuel. Wing flaps were retracted. The engine was developing significant power on impact. The pilot, the sole occupant, sustained fatal injuries. The aircraft was destroyed; there was no post-impact fire. The 406-MHz emergency locator transmitter activated on impact.
Flight Following and ELT Data
C-GRGW was equipped with a SkyTrac Systems ISAT 100 GPS-based flight-following system transmitting time, location, altitude, heading, and ground speed at 5-second intervals. Data ended at 1707:07, before the final minutes. At 1734, an ELT signal was received; initial location was 67 nm northeast of the site. The last SkyTrac transmission at 1732 showed the aircraft at 4849 feet asl, heading 080° true, ground speed 76 knots, coinciding with the accident site.
Conduct of Pipeline Patrols
Pipeline patrols are normally flown with a single pilot-observer. At points of interest, pilots would circle to the left at altitudes between 200 and 700 feet above ground level, using a hand-held DSLR camera. The pilot had taken 90 photographs on the accident flight. A sequence of five photos showed the aircraft directly over the Chaffen Creek crossing; the last photo indicated a 45° bank angle at about 350 feet agl on a southerly heading. SkyTrac data showed two left turns about 30 nm north of the site with average bank angles of 46° and 51°, and average ground speeds of 93 and 103 knots.
Pilot Experience
The pilot was certified and qualified, with approximately 6900 total flying hours, about 5000 hours on Cessna 172 pipeline patrols since 2003. The pilot last flew on 21 August and was reported well rested and in good spirits.
Company
Alta Flights Ltd. operated under Canadian Aviation Regulations Subparts 702 (Aerial Work), 703, and 704. The company had a Safety Management System implemented in February 2011. A risk management worksheet identified bank angles of 35° to 40° below 1000 feet agl as a risk, with risk-control being enhanced ground-school training. The probability of hazard was assessed as low because inspections were carried out at near-maximum cruise airspeeds.
Meteorological Conditions
The nearest weather report (Alberta Forest Service Willow Creek station, 11 nm northeast) at 1800 recorded temperature 19°C, dewpoint 6°C, wind 5 knots gusting 12 knots. Pilot photographs showed unlimited visibility and clear sky. There was a risk of light carburetor ice at any power setting above descent power.
Aircraft Performance
C-GRGW was certified and maintained per regulations with no known deficiencies. It was equipped with main tanks (190 litres), wing auxiliary tanks (87 litres), and a baggage compartment tank (68 litres) under supplemental type certificates. At the accident time, weight was 2306 pounds (below max 2550), centre of gravity 45.9 inches aft of datum (aft limit 47.3 inches).
Stall/Spin Characteristics
Under conditions from the last photo (45° bank, weight 2300 pounds, flaps up, aft CG), the Cessna 172M aerodynamic stall speed would have been 59 KCAS. At 60° bank, stall speed would be 71 KCAS. The aircraft entered a spin and did not recover.