Rocky Mountain Airways Flight 217

Rocky Mountain Airways Flight 217, referred to in the media as the "Miracle on Buffalo Pass", was a scheduled domestic passenger flight from Steamboat Springs, Colorado to Denver that crashed on Buffalo Pass. The aircraft, a de Havilland Canada DHC-6 Twin Otter 300, impacted terrain on a gentle slope and was partially buried in snow. All of the 22 passengers and crew survived the impact, but a female passenger died before rescue could arrive, and the captain died of his injuries 3 days after the accident. The investigation, conducted by the National Transportation Safety Board, determined that formation of ice on the wings combined with downdrafts associated with a mountain wave led to conditions which were beyond the aircraft's ability to maintain flight. Contributing to the accident was the captain's decision to fly into weather conditions that were beyond company's limitations.

Flight

Rocky Mountain Airways Flight 217 was intended to depart Steamboat Springs Airport at 16:45, but was delayed because the inbound flight from Stapleton International Airport, Flight 216, arrived at 18:21 due to a delayed departure from Stapleton and strong headwinds en route. The crew reported that they encountered heavy rime icing during the descent into Steamboat Springs but the flight was otherwise smooth and without turbulence. Both the captain and first officer had to remove ¾ inches (1.9 cm) of ice from the aircraft after landing.

Captain Klopfenstein planned a flight plan using instrument flight rules (IFR) between Steamboat Springs Airport and the Gill VOR along the V101 airway at 17,000 ft and from Gill, proceed with visual flight rules (VFR) to Denver.

Accident

Flight 217 departed from Steamboat Springs at 18:55, two hours and ten minutes behind schedule, and was cleared to climb to its assigned altitude of 17,000 ft. First Officer Coleman, who was in command of the flight, flew the aircraft following the published departure for the airport, reversed course at 10,000 ft, crossed the non-directional beacon (NDB) over Steamboat Springs Airport at 12,000 ft, and intercepted the V101 airway flying east. The aircraft encountered minor freezing precipitation and entered a cloud bank as it was climbing over Buffalo Pass. The Twin Otter encountered severe icing conditions on the aircraft's propellers and windshield, but the aircraft's deicing systems was able to remove the ice. The flight was able to climb up to 13,000 ft, but neither the first officer nor the captain was able to make the aircraft climb to a higher altitude at the normal engine power settings. Due the aircraft's inability to reach an altitude above 13,000 ft before the Kater intersection, a point at the intersection of two radials, the captain elected to return to Steamboat Springs at 19:14, without informing the passengers.

Flight 217 transmitted to Denver Center, the air traffic control (ATC) in contact with the flight, that they would have to return to Steamboat Springs. Denver Center soon called the station agent at Steamboat Springs, telling him that Flight 217 was returning to airport. Later, the flight reported that they had encountered heavy icing conditions and that they recommended that no other flights should attempt to fly in the area. The flight turned back west and soon crossed the 335° radial from the Kremmling VOR. At this time, the flight encountered its first severe icing conditions while returning for approximately 12 seconds. The flight descended uncommanded from 13,000 ft to 11,600 ft before Captain Klopfenstein was able to extend the flaps on the wings. At this time, the flight had an indicated airspeed of 90-100 knots and roughly 1.5-2 in thick ice. At 19:39, the aircraft transmitted, "...want you to be aware that we're having a little problem here maintaining altitude and proceeding direct Steamboat beacon." Denver controllers offered their assistance, but the flight replied with, "not now," which would be the final transmission from the flight. Shortly after this transmission, the aircraft encountered another area of severe icing. This resulted in the Twin Otter beginning another uncontrolled descent at a rate of 800–1,000 fpm, even with the engines at maximum climb power. Shortly before impact, the first officer advanced the engine levers to maximum takeoff go-around power, selected fully extended flaps, and told the captain to bank right. However, the aircraft's right wingtip impacted a high-voltage electrical tower, causing a short circuit and a power outage in the nearby town of Walden. At 19:45, Flight 217 impacted the ground near another electrical tower, coming to rest on its right side, without its left wing and with a severely damaged right wing. The wreckage distributed on a 200 ft was on a 1–6° slope, partially buried in snow at an elevation of 10,530 ft. The aircraft remained mostly intact, although the fuselage around the wing fittings had openings in them.