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Last updated: 27 November 2021
Statuts:Enquête Officielle
Date:mardi 27 février 1979
Heure:08:07
Type/Sous-type:Silhouette image of generic DHC6 model; specific model in this crash may look slightly different
de Havilland Canada DHC-6 Twin Otter 300
Compagnie:Rocky Mountain Airways
Immatriculation: N24RM
Numéro de série: 372
Année de Fabrication: 1973
Heures de vol:16024
Moteurs: 2 Pratt & Whitney Canada PT6A-27
Equipage:victimes: 0 / à bord: 2
Passagers:victimes: 0 / à bord: 14
Total:victimes: 0 / à bord: 16
Dégats de l'appareil: Substantiels
Conséquences: Repaired
Lieu de l'accident:2,4 km (1.5 milles) E of Cheyenne Airport, WY (CYS) (   Etats-Unis d'Amérique)
Phase de vol: En montée initiale (ICL)
Nature:Transport de Passagers Nat.
Aéroport de départ:Cheyenne Airport, WY (CYS/KCYS), Etats-Unis d'Amérique
Aéroport de destination:Denver-Stapleton International Airport, CO (DEN/KDEN), Etats-Unis d'Amérique
Numéro de vol: 801
Détails:
Rocky Mountain Airways Flight 801, crashed into rolling terrain shortly after takeoff in visual flight conditions from runway 34 at Cheyenne Municipal Airport, WY (CYS). Two passengers were injured slightly.
The DHC-6 Twin Otter had arrived at Cheyenne at 07:56 after a flight from Denver. Fourteen passengers boarded for the return flight to Denver. The left engine was restarted and at 08:03, the aircraft was taxied to the threshold of runway 34 for takeoff. The tower gave the flight an IFR clearance to Denver. About 08:05, after selecting 10 degrees of flaps and arming the propeller autofeather system, the crew began takeoff.
According t o the first officer, near 65 kts, back pressure was applied to the control wheel and shortly thereafter, the aircraft lifted off. The aircraft continued to accelerate after liftoff to about 90 kts, the best-angle-of-climb speed.
About 150 ft agl, the captain heard a bang and a roaring noise as the aircraft yawed to the right. The prop autofeathered and the airspeed dropped from 90 kts to 85 kts.
The flight crew stated that since they could not maintain both altitude and airspeed they were forced to sacrifice altitude to maintain flying speed. When it became apparent that a forced landing was inevitable, the aircraft was turned toward an open area; the speed of the aircraft was 82 kts. The flaps remained at 10 degrees to aid in choosing a landing spot among the large knolls on the terrain. The first touchdown was made close to stall speed, and on the main gear on the upslope of a large, grassy knoll. A slight dip in the knoll caused the aircraft to bounce slightly. The aircraft became airborne again as it traversed the crest of the knoll and then touched down again on another knoll about 30 yards away. They stated that the aircraft again became airborne and it was necessary to use some power to prevent a stall on the downslope side of the second knoll. The aircraft touched down a third time on top of a fence which surrounded a fire station. The left main landing gear separated from the aircraft. The aircraft slid through a chainlink fence and hit several barrels of oil located behind the fire department. The barrels of oil ignited, but the aircraft slid past them and did not catch fire. The aircraft came to a stop about 30 yards past the fence.

Probable Cause:

PROBABLE CAUSE: "The National Transportation Safety Board determined that the probable cause of the accident was the flight crew's erroneous determination that the aircraft was not capable of single-engine flight and their actions which precluded obtaining maximum available performance from the aircraft. The cause of the engine failure was an erroneous assessment by company maintenance personnel of damage sustained by the right engine during an overtemperature condition and their poor judgment in deciding to repair and release the engine for flight without replacing the engine's power turbine section."

Accident investigation:
cover
Investigating agency: NTSB
Status: Investigation completed
Duration: 142 days (5 months)
Accident number: NTSB/AAR-79-10
Download report: Final report


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Plan
Ce plan montre l'aéroport de départ ainsi que la supposée destination du vol. La ligne fixe reliant les deux aéroports n'est pas le plan de vol exact.
La distance entre Cheyenne Airport, WY et Denver-Stapleton International Airport, CO est de 152 km (95 miles).

Les informations ci-dessus ne représentent pas l'opinion de la 'Flight Safety Foundation' ou de 'Aviation Safety Network' sur les causes de l'accident. Ces informations prélimimaires sont basées sur les faits tel qu'ils sont connus à ce jour.
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