On March 7, 1994, a Cessna 170B (registration N4310B) operated by Michael A. Petrie was involved in an aviation accident near Chugiak, AK. Investigators recorded the probable cause as: THE PILOT-IN-COMMAND'S IMPROPER INFLIGHT DECISION MAKING. FACTORS CONTRIBUTING TO THE ACCIDENT WERE THE MOUNTAINOUS TERRAIN AND THE DOWNDRAFT WEATHER CONDITIONS. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A pilot attempting to navigate up a valley encountered strong downdrafts that prevented maintaining altitude despite full power application, resulting in an emergency landing in deep snow on a steep incline.
What happened
The pilot was operating the aircraft when he attempted to fly up a valley. During this phase of flight, he encountered significant downdrafts that affected the aircraft's performance. To counteract the loss of altitude caused by these downdrafts, the pilot applied full power to maintain his current height.
Despite applying maximum available power, the pilot did not have sufficient airspeed to execute a turn out of the valley. The lack of airspeed rendered the aircraft unable to maneuver effectively within the confined space of the valley. Consequently, the pilot was forced to make an emergency landing in deep snow on a steep incline. This landing occurred at the 3000 ft level, which was located 100 feet below the ridge line.