Investigation Summary
The flight departed Steamboat Springs over two hours behind schedule into known winter weather. Earlier that day, the same crew had attempted a flight to Steamboat Springs but were forced to return to Denver due to severe downdrafts. Before the accident departure, the crew had manually cleared approximately 0.75 inches of ice from the airframe. During the climb toward its assigned altitude of 17,000 feet, the aircraft encountered minor freezing precipitation that quickly escalated into severe icing. The crew found the aircraft unable to climb above 13,000 feet, leading Captain Klopfenstein to elect to return to Steamboat Springs. During the return, the aircraft was caught in a mountain wave, a meteorological phenomenon where stable air flowing over mountain ridges creates intense vertical oscillations. These downdrafts, combined with heavy ice accumulation on the airframe, forced the Twin Otter into an uncommanded descent. Despite the crew applying maximum takeoff power and extending flaps to increase lift, the aircraft continued to lose altitude at a rate of 800 to 1,000 feet per minute. The right wingtip struck a high-voltage electrical tower, causing a blackout in the town of Walden, which inadvertently helped searchers locate the general crash area. The aircraft came to rest on a steep, snow-covered slope, where survivors endured temperatures as low as -50 F and 40 mph winds for over 10 hours before rescue teams reached them.
Final Conclusions
The NTSB determined the probable cause was the aircraft's encounter with severe icing conditions and a high-velocity downdraft (mountain wave) which exceeded the climb capability of the aircraft. A contributing factor was the captain's decision to initiate the flight into known icing conditions, which exceeded the conditions under which the company authorized flight. The investigation noted that while the captain was aware of the icing, the specific mountain wave conditions were not mentioned in his meteorological briefings and were likely masked by other weather phenomena during his previous flights that day.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Scott Alan Klopfenstein, age 29.
First Officer
Gary Coleman, age 34.
Systems & Failure Modes
Deicing Systems
The DHC-6 was equipped with deicing boots and propeller heat; while these functioned to remove ice, the sheer volume of accumulation and the force of the downdrafts exceeded the aircraft's performance limits.
High-Voltage Electrical Tower
The aircraft's right wingtip struck a high-voltage electrical tower, causing a short circuit that alerted local authorities to the crash location when the town of Walden lost power.
Interesting Facts
- 01The crash caused a power outage in Walden, Colorado, which helped rescuers narrow the search area.
- 02The aircraft remained mostly intact despite the impact, providing a shelter that was critical for survival in the blizzard.
- 03The aircraft came to rest on its back (inverted) after striking the ground.
- 04Rescuers had to travel 15 miles in open snow cats to reach the crash site.
- 05The female passenger who died succumbed to her injuries approximately four hours after the crash while still at the site.
- 06Captain Scott Alan Klopfenstein died of his injuries in a hospital approximately 70 hours (3 days) after the accident.
- 07One infant was among the 20 passengers on board; all passengers initially survived the impact.
Safety Actions & Advisories
Departure Procedure Revision
The departure procedure for Steamboat Springs was modified to allow aircraft to gain more altitude while flying westward before turning east over the mountain ranges.