DEN01LA050

**This report was modified on 2/18/2016. Refer to the public docket for this accident for an explanation of the changes.**

After completing a flight from Washington, DC, and after touchdown on runway 29, the airplane departed the left side off the runway and came to rest in the snow. The left main landing gear collapsed and the left wing, wing slats, and the No. 3 engine nacelle were damaged. Examination of the brake system found an electrical anomaly in one of two tacho-generators in the right main landing gear. Postaccident testing determined that the anomaly was not sufficient to affect brake performance. Analysis of cockpit voice recorder (CVR) information, weather data, and runway conditions indicated that the flight crew flew a straight-in global positioning system/non-directional beacon approach to runway 29. CVR and weather information indicated that both approaches to runway 29, including a missed approach, were flown below reported approach minimums of 2 miles visibility, although after the accident, the flight crew reported they had the runway in sight at 2 miles on the second approach. CVR information indicated that the final approach was unstabilized and required airplane configuration changes and maneuvering at a low altitude. Postaccident runway evidence (tire tracks on the snow-covered runway) indicated that the Falcon's right main landing gear touched down left of the runway centerline. The airport manager reported that light snow covered the runway and that there was no evidence of skidding.

**This report was modified on 2/18/2016. Refer to the public docket for this accident for an explanation of the changes.**

On February 6, 2001, at 2050 mountain standard time, a Dassault-Breguet Mystere Falcon 900 airplane, N59CF, sustained substantial damage when it departed the side of the runway during landing roll at Pinedale, Wyoming. The airline transport certificated pilot and co-pilot, the flight attendant, and the 5 passengers were not injured. The flight was operating on an instrument flight rules flight plan under Title 14 CFR Part 91. The flight originated from Ronald Reagan Memorial Airport, Washington, DC, at 1826 eastern standard time. Instrument meteorological conditions prevailed for the landing at Pinedale.

CVR information reviewed by Safety Board investigators determined that the flight crew flew two straight-in approaches to runway 29 at Pinedale Airport. Both approaches, including the first missed approach, were flown with visibility reported as 1 3/4 miles, below instrument flight rules minimums of 2 miles. After the accident, the flight crew reported that they had the runway in sight at 2 miles on the second approach. CVR information also indicated that the airplane's ground proximity warning system activated with "sink rate" and "pull up" alerts during final approach and that the flight crew used air brakes during the descent and just before touchdown to slow the airplane, contrary to the Falcon's airplane flight manual. The pilot-in-command, who was the pilot not flying seated in the right seat, stated that the "final approach to the runway was on speed and stable. Round out was normal just to the left of centerline." He added that the runway was reported to the flight crew as "clear/dry." Weather at the time of the accident was reported as visibility between 3/4 and 1 3/4 miles, ceiling 800 feet to 1,000 feet overcast, winds 4 knots from 290°, with light and blowing snow.

According to the flight crew, immediately after touchdown, the airplane pulled to the left and corrective action, including nose-wheel steering and differential braking, did not prevent the airplane from exiting the left side of the 100-foot wide runway. The airplane came to rest opposite the landing direction in snow-covered terrain about 30 feet left of the edge of runway 29. The left main landing gear collapsed, and the left wing, left wing slats, and the No. 3 engine nacelle were damaged.

Tests on the airplane's anti-skid system at a contract facility in Florida determined that one of two tacho-generators from the right main landing gear was not operating according to design specifications listed in brake manufacturer Messier-Bugatti's component maintenance manual (CMM). The tests determined that tacho-generator serial no. 180 had an armature resistance of 1198 to 1581 ohms, rather than 550 ohms and 750 ohms, as specified in the CMM. Subsequent testing and analysis in 2002 by Messier-Bugatti confirmed that the initial, postaccident tests indicated an out-of-specification condition for the serial no. 180 tacho-generator but that brake performance was not affected. Subsequent testing by Messier-Bugatti determined that the anomaly produced about a 1 percent variation in release current, with no impact on brake performance. Safety Board airplane systems specialists in Washington, DC, reviewed Messier-Bugatti's postaccident test protocols and results.