SEA97FA076

Before flight, both wing fuel tanks were 'topped off' with 50 gallons of usable fuel. At about 0950 MST, the pilot departed Worland, Wyoming, en route to Cody, Wyoming, to commence the second half of an aerial pipeline patrol route. After an estimated 20 minutes of flight, the aircraft crashed in an area of uneven, sage covered, terrain. The flaps were found extended 8 degrees, the ignition had been switched to 'LEFT,' and there was evidence that the pilot had slowed the aircraft before it impacted uneven terrain. No evidence was found to indicate that the engine was developing power when impact occurred; aft bending of the propeller was noted with minimal abrasion and chordwise scratching. Extensive hydraulic effect was noted on both main fuel tanks, as well as on one of the brass floats within the carburetor float chamber. An engine teardown revealed no preimpact mechanical malfunction, and no anomaly was found with the aircraft's fuel, air, or ignition systems. Postcrash testing of the aircraft's auxiliary fuel system revealed no mechanical malfunction. Temperature and due point at Worland were 54 and 32 degrees; according to icing probability charts, these conditions were conducive for carburetor ice; however, carburetor icing was not verified.

History of flight

On March 26, 1997, approximately 1010 mountain standard time, a Cessna 172P, N97527, registered to and being operated by Brentco Aerial Patrol, Inc., and being flown by a commercial pilot, was destroyed during impact with terrain following a loss of control in flight approximately 11 nautical miles (nm) south-southwest of Burlington, Wyoming. The pilot was fatally injured. Visual meteorological conditions existed and no flight plan had been filed. The flight, which was an aerial pipeline patrol, was to have been operated under 14CFR91, and originated from Worland, Wyoming, approximately 0950.

According to personnel stations at the operator's base at Durango, Colorado, the pilot departed Bridger, Montana, where he based the aircraft, and commenced an aerial pipeline patrol flight sometime early on the morning of Wednesday, March 26, 1997. Several credit card receipts were found showing fuel purchased at the fixed base operator at the Worland, Wyoming airport. These receipts provided the following information:

Monday (03/24/97) 07:48AM 28.6 gallons 100LL avgas Tuesday (03/25/97) 10:18AM 39.0 gallons 100LL avgas Wednesday (03/26/97) 09:48AM 34.7 gallons 100LL avgas

The fueler at the Worland airport reported that he was accustomed to seeing N97527 stop for fuel. He also reported that on the morning of Wednesday, March 26, he topped off the wing fuel tanks after which the aircraft immediately departed (note the time of the credit card transaction shown at 0948).

The operator reported that the pilot was contractually required to patrol each of the designated pipeline routes a minimum of once per week. The pilot was given flexibility as to when to conduct the various patrol flights and in what order.

The aircraft's emergency locator transmitter (ELT) operated subsequent to the accident and signals were reported to Seattle Air Route Traffic Control Center at 1135. The aircraft was subsequently visually located at 1544.

The aircraft was found at a point 32 nm west-northwest of the Worland airport, and on a direct line toward the Cody airport (refer to CHART I). Documentation found at the crash site showed a series of patrol routes, of which one was observed to begin at a point named Silver Tip (arrow A on CHART I) and continue southeast past the Worland airport and thence southwest and west to a point named Gooseberry (refer to CHART I). An intermediate point on this route named Slick Creek was observed to lie just east of the Worland airport (refer to arrow B on CHART I, and CHART II). Additionally, a separate portion of this route was observed to begin just east of the Cody airport at Cody Booster (refer to arrow C on CHART I, and CHART II) and terminate approximately 10 nm southeast of the airport at Oregon Basin (refer to CHART II). This termination point was approximately 25 nm north of Gooseberry (refer to ATTTACHMENT I which names the patrol route points for the entire route).

Personnel information

No pilot logbooks were located and the flight time entered into the core report were provided by the Operator. The pilot was hired by the Operator on February 6, 1996, and began flying pipeline patrol flights in the Southwest (Texas-New Mexico) shortly thereafter. He was transferred to pipeline routes in Wyoming on January 29, 1997, and moved to Bridger, Montana (refer to CHART I).

N97527 was, according to the Operator, assigned to the pilot after he was hired. According to the airframe log, the aircraft accrued approximately 1,109 hours for flight time between February 18, 1996, and the date of the accident.

Aircraft information

N97527, a Cessna 172P, was equipped with two 27 gallon metal fuel tanks, one located in each wing root area. Or the 27 gallons available in each tank, all but 2 gallons were usable. The fuel is fed by gravity from the wing tanks through a four position selector valve and on to the carburetor. The selector valve positions are (from the 6 o'clock position clockwise) OFF, LEFT, BOTH, and RIGHT.

Additionally, the aircraft had been modified per Supplemental Type Certificate SA615NE, dated 10/18/88, to include an 18 gallon aft baggage compartment fuel tank. The aluminum tank was serviced through a filler port on the right side of the fuselage (refer to photograph 4). Fuel within the tank was transferred via an electric pump into the right wing tank. The tank was equipped with both a sump drain and vent line.

The transfer pump was operated via a control panel located immediately aft of the fuel selector valve on the floor of the cockpit and between the front seats. The control panel was equipped with a round, analog fuel gauge located in the center with marked positions showing "E" (empty), "1/2" and "F" (full). A three position switch controlling the electric pump was located to the left of the gauge and a single, small incandescent light was located to the right of the gauge.

The axis of the toggle switch, which in its mid position, was normally parallel to the aircraft's vertical axis, could be moved aft to the OFF position, or forward to the START position. THE START (forward) position was spring loaded such that the switch, when released, would return to the mid position, marked RUN. The OFF (aft) position was not spring loaded (refer to photograph 19).

Operating procedures for the fuel transfer system were to:

1. "Operate on main tanks until right fuel gauge reads 2/3 full." 2. "Move transfer switch to momentary position and hold for 10 seconds. Light should illuminate and remain illuminated when switch is released." 3. "If light does not stay illuminated, repeat step 2." 4. "Transfer while operating on right main tank in straight and level flight only." 5. "Transfer is in progress when transfer light is illuminated." (refer to ATTACHMENT M pages 1-4)

Meteorological information

The aviation surface weather observation taken at Cody, Wyoming at 0855 on the morning of the accident reported winds from 220 degrees magnetic at 13 knots with gusts to 17 knots. One hour later (0955) the station reported winds from 260 degrees magnetic at 13 knots with gusts of unreported intensity.

The aviation surface weather observation taken at Worland, Wyoming, at 0855 on the morning of the accident reported winds from 310 degrees magnetic at 3 knots. One hour later (0958) the station reported winds from 300 degrees magnetic at 3 knots. Winds remained light throughout the day with no gusts reported.

Wreckage and impact information

The ground impact site was established at 44 degrees 17.078 minutes north and 108 degrees 33.262 minutes west latitude and longitude respectively using a hand held global positioning unit. The elevation of the site was approximately 5,850 feet above mean sea level. The terrain at the site was characterized by uneven, sage covered terrain with numerous moderate slope changes (refer to CHART III).

According to personnel responding from the Big Horn County Sheriff's office, the aircraft was observed by search and rescue personnel at the accident site in a nose low, nearly vertical attitude with respect to the terrain. During the night following the accident strong winds reportedly blew the aircraft over onto its back.

The investigative team observed the aircraft in an inverted attitude with the longitudinal axis oriented along a 091/271 degree magnetic bearing line (tail east). The slope at the initial impact site was measured at -35 degrees towards the east-northeast. The crush along the underside of the aircraft's engine/forward fuselage was measured to be approximately 27 degrees. The left wing was observed to be displaced aft somewhat of the aircraft's lateral axis, whereas the right wing was displaced forward to the same approximate degree. The left main landing gear displayed greater aftward deformation compared to the right main landing gear. The auxiliary fuel tank cap was observed hanging