Accident Overview
On a visual flight rules pipeline patrol flight, a Cessna 172L aircraft (serial number 17260159) departed Trenton, Nova Scotia, at 1120 Atlantic standard time. The aircraft was flying along the Halifax lateral portion of the patrol when, at approximately 1445, it struck a tree and crashed to the ground. Snowmobilers located the wreckage at 1615 alongside the pipeline, approximately 31 miles northeast of Halifax International Airport. The pilot, the sole occupant, sustained fatal injuries, and the aircraft was destroyed.
Flight Details
The pilot had flown from Trenton to Port Hawkesbury to start the patrol and was on the fifth leg, the Halifax lateral portion, from the Tufts Cove power generating station to the junction of the main pipeline near New Glasgow. Radar data showed the transit leg flown at approximately 4600 feet above sea level (asl) with a ground speed of 120 knots. The highest obstacle in the area was approximately 1600 feet asl. Upon reaching the start of the patrol, the aircraft descended to between 400 and 550 feet above ground level (agl) and remained there until just south of Halifax International Airport. The pilot communicated normally with Halifax tower while transiting the control zone. While in the zone, the aircraft descended further, and the remainder of the flight captured on radar was flown at altitudes between 150 and 450 feet agl, with the majority between 150 and 250 feet agl. At one point, approximately seven nautical miles northeast of the airport, the aircraft briefly disappeared from radar. Throughout this portion, the aircraft closely followed the pipeline track and terrain contours. The last radar return was 19 nm northeast of the airport at an altitude between 350 and 450 feet agl, approximately 14 minutes before the accident.
Contract and Operational Context
The Nova Scotia pipeline aerial patrols were contracted to Coastal Aviation Ltd. by Maritimes & Northeast Pipeline. The contract called for weekly patrols at an altitude of about 1000 feet agl, or lower at the pilot's discretion. The aircraft operator reported that patrols were normally flown at 500 feet agl, and industry common practice is 500 to 700 feet agl.
Weather Conditions
Weather at Halifax International Airport at the time was: winds 310° at 7 knots, visibility 15 statute miles, sky clear, temperature minus 7°C, dewpoint minus 18°C.
Accident Site and Impact
The accident site was in a snow-covered, clear-cut area on the east side of the pipeline, just beyond a small grove of trees. The clear-cut area extends approximately one mile back along the flight path before reaching a large uncut area. The terrain gently up-slopes from the uncut area to beyond the site. The right wing, right wing strut, and right main landing gear tire struck the top portion of a spruce tree that was protruding above other trees, breaking it off at approximately 55 feet agl. The impact caused the right wing to separate. The aircraft then rolled inverted and travelled 547 feet before striking the ground in an 80-degree nose-down, inverted attitude. After impact, it flipped over and came to rest upright, facing the opposite direction. Tree impact damage corresponds to a wings-level attitude at initial impact.
Wreckage Examination
Examination confirmed flight control system continuity at impact. No pre-impact discrepancies were found that would have affected operation. Although the fuel system was compromised, traces of fuel were found, and a fuel sample from the gascolator was free of contamination. Propeller damage was consistent with engine power at impact. The engine tachometer indicated an rpm of 2350, consistent with cruise power. The exhaust system showed normal light tan deposits. The emergency locator transmitter was extensively damaged and unable to transmit.
Pilot Information
The pilot obtained his commercial pilot license in July 2001 and started working for Coastal Aviation Ltd. in October 2001. The accident flight was his 12th pipeline patrol since checkout on 03 December 2001. He had 361 total flying hours, 336 of which were in Cessna 172 aircraft. He was qualified for the flight.
Medical and Toxicology
Autopsy results revealed no pre-existing medical condition that would have contributed. Toxicology tests for alcohol and drugs were negative. Blood analysis identified a low level of carbon monoxide (10% saturation), deemed not to have an adverse effect on performance.
Findings as to Causes and Contributing Factors
The investigation found that the pilot consistently flew the aircraft below the required altitude for effective observation and inadvertently struck a tree.