Aviation Accident Summaries

Aviation Accident Summary WPR09LA043

Hanna, UT, USA

Aircraft #1

N8387N

CESSNA 170B

Analysis

The pilot checked the weather forecast twice prior to departing on the cross-country flight, with both reports indicating that visual flight rule (VFR) conditions would prevail. The pilot stated that after taking off and climbing to an altitude of 10,500 feet mean sea level (msl), he was able to survey the approaching mountain and its summit, and initiate a rate of climb that would clear the terrain. As the flight approached the mountain, the flight encountered increasing tailwinds that reduced the effective altitude gain over distance traveled to an amount insufficient to clear the terrain. The pilot reported that as the mountain range approached he encountered unusually strong downdrafts in relation to terrain contours leading to the summit. The pilot further stated, "...we also began experiencing a loss in altitude, speed, and rate of climb, as well as increasingly adverse terrain, causing our speed to become too slow for a safe turn without further loss of control or altitude with the increasing elevation." As the airplane was losing altitude, the pilot elected to pick out a clearing to make a forced landing, as the airspeed was too low for an evasive maneuver. The airplane impacted terrain in a snow-covered clearing at an elevation of 9,800 feet msl, coming to rest upright in an open meadow surrounded by mountainous terrain about 150 feet from the initial touchdown point. The airplane sustained substantial damage to both wings and fuselage. The pilot reported no mechanical failures or malfunctions with the airplane at the time of the accident.

Factual Information

On November 21, 2008, about 1130 mountain standard time (MDT), a Cessna 170B, N8387N, sustained substantial damage following a forced landing in mountainous terrain about 12 nautical miles northwest of Hanna, Utah. The pilot and right front seat passenger sustained serious injuries, and the left rear seat passenger was killed. Visual meteorological conditions prevailed for the personal cross-country flight, which was conducted in accordance with 14 Code of Federal Regulations (CFR) Part 91. A flight plan was not filed. The flight departed the Salt Lake City International Airport (SLC), Salt Lake City, Utah, about 1030. Its destination was the Garfield County Regional Airport (RIL), Rifle, Colorado. In a statement submitted to the Safety Board investigator-in-charge (IIC), the pilot reported that he checked the weather for the route of flight the day before and the morning of the accident, which indicated that visual flight rules (VFR) conditions were forecast. The pilot further reported that after taking off and climbing to an altitude of 10,500 feet mean sea level (msl), "...we were able to visibly survey the approaching mountain and its summit, and prepare an acceptable rate of climb to clear the terrain, while adjusting for moderately increasing tailwinds." The pilot stated that as the mountain range approached he encountered unusually strong downdrafts in relation to contours leading to the summit. The pilot further stated, "...we also began experiencing a loss in altitude, speed, and rate of climb, as well as increasingly adverse terrain, causing our 'flight speed' to become too slow for a safe turn without further loss of control or altitude with the increasing elevation. [I] began looking for a direct level clearing for an emergency landing." The pilot reported that [his] efforts were focused on controlling the approach with flaps in the optimal climb position, "...but the aircraft continued losing altitude despite full engine power. The aircraft impacted the ground in a tree clearing in approximately 18 inches of snow." Recovery personnel reported to the IIC that the airplane came to rest upright in an open meadow surrounded by rising mountainous terrain about 150 feet from the initial touchdown point. The accident site was located about 87 nautical miles northwest of SLC, at an altitude of about 9,800 feet mean sea level. The recovery team reported that both wings remained attached to the airplane, the main landing gear separated from the fuselage, and the fuselage partially separated at the aft cabin bulkhead area. Additionally, the airplane's engine had separated and came to rest about 10 feet in front of the main wreckage. About 7 gallons of aviation fuel was drained from both wing tanks. An examination of the airplane under the supervision of a Federal Aviation Administration (FAA) airworthiness inspector revealed that flight control continuity was established throughout the airplane, the flap handle was in the first detent, the 10 degree position, and the fuel selector handle was in the BOTH position. The propeller remained attached to the engine. Both blades exhibited leading edge damage, tip curling, and "S" bending. One propeller tip displayed a semi-circular separation on the leading edge of the tip and was bent aft about 30 degrees starting about 12 inches from the hub. The remaining blade was bent aft about 15 inches, starting at the hub and progressing outward to the propeller tip. The outboard 1 inch of the tip was curled aft about 80 degrees. The pilot reported to the IIC that there were no anomalies with the airplane prior to or during the en route portion of the flight. The pilot stated, "It was working just fine." At 1053, the Automated Surface Observing System (ASOS) at the Salt Lake City International Airport (SLC), Salt Lake City, Utah, located 87 nautical miles northwest of the accident site, reported winds from 350 degrees at 6 knots, visibility 10 statute miles, few clouds at 13,000 feet, scattered clouds at 17,000 feet, broken clouds at 20,000 feet, temperature 6 degrees Celsius, dew point minus 4 degrees Celsius, and an altimeter setting of 30.36 inches of Mercury.

Probable Cause and Findings

The flight's encounter with adverse tailwinds and downdrafts in mountainous terrain that exceeded the airplane's climb capability.

 

Source: NTSB Aviation Accident Database

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