What happened
On the night of April 22-23, 1953, an N1693M Boeing aircraft, operated by American Air Transport, Inc., was performing a ferry flight from Columbia, South Carolina, to Seattle, Washington. After an initial leg to Cheyenne, Wyoming, the crew transitioned to a new flight plan. Following a departure from Cheyenne, the flight proceeded under VFR conditions through Idaho and Oregon before transitioning to IFR operations.
As the aircraft approached Washington, the pilot received instructions to descend from 8,000 feet toward Boeing Field. At approximately 0048, the pilot contacted Seattle Center to report passing over Easton at 8,000 feet. The controller issued a clearance instructing the aircraft to cross Hobart at 8,000 feet and then descend to at or above 4,000 feet. During the read-back, the pilot incorrectly understood the instructions regarding both the crossing altitude and the reporting procedures. While the controller corrected the error regarding the reporting station, the misunderstanding of the altitude requirement remained uncorrected.
Following this communication, no further transmissions were received from the aircraft. After the flight failed to arrive at its destination and missed a scheduled report over Hobart, search and rescue operations were launched. The wreckage was located the following day near a mountain crest, where two survivors were recovered.
Findings
Investigations into the accident determined that the primary cause was the pilot's failure to correctly interpret the ATC clearance, which led to a failure to verify required altitudes against navigational charts and an unauthorized descent below the minimum en route altitude. The aircraft struck terrain at approximately 4,000 feet MSL after descending below the prescribed 8,000-foot limit.
Additional contributing factors included:
- The controller's failure to identify the pilot's incorrect read-back regarding the crossing altitude.
- Potential physiological factors, specifically that the crew may have suffered from fatigue and hypoxia.
- No mechanical failures or malfunctions were identified in the aircraft components.