Investigation Summary
Flight 2 was an eastbound multi-stop service scheduled from Seattle to Chicago, with intermediate stops at Spokane, Butte, and Billings. After departing Butte, Montana, the crew diverted north of their usual course to avoid a dust storm over Bozeman Pass. At 15:05 MST, the first officer reported reaching their cruising altitude of 9,000 feet. Shortly thereafter, ground witnesses observed the aircraft drop suddenly, enter a stall, and spin into a snow-covered peak. The wreckage was found charred and twisted, with the tail surfaces missing from the main impact site. Investigators determined that the twin-tail design was susceptible to flutter, a phenomenon where aerodynamic forces cause surfaces to vibrate uncontrollably until they fail. The investigation revealed that Lockheed's original vibration testing equipment had provided inaccurate data, leading to an underestimation of the aircraft's natural vibration periods. The severe turbulence encountered near the Bridger Range acted as the trigger for this catastrophic structural failure.
Final Conclusions
The Investigating Board concluded that the probable cause was a structural failure of the upper vertical fins and rudders due to flutter, which resulted in a total loss of control. The flutter was likely initiated by severe to extreme turbulence encountered during the flight.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Nick B. Mamer
Systems & Failure Modes
Empennage (Tail Section)
The twin-tail assembly, consisting of two vertical fins and rudders, failed structurally in flight due to aeroelastic flutter.
Lockheed Vibration Testing Machine
The equipment used by Lockheed to measure natural vibration periods was found to be inaccurate, leading to a design that did not sufficiently account for flutter risks.
Interesting Facts
- 01This was the first fatal crash of a Lockheed Super Electra aircraft.
- 02The aircraft was brand new, having been manufactured in 1937 with MSN 1407.
- 03The Department of Commerce grounded all Lockheed Super Electras within 24 hours of the accident.
- 04Testing after the crash revealed that Lockheed's vibration measurement machines had given misleading results during certification.
- 05The pilot, Nick Mamer, was a well-known aviation pioneer with over 10,000 flying hours.
Safety Actions & Advisories
Fleet Grounding
The Department of Commerce ordered the immediate grounding of all Lockheed Super Electras following the crash to investigate structural integrity.
Rudder Modification
Authorities ordered all Super Electra rudders to be modified to eliminate the possibility of flutter causing in-flight break-ups.