Investigation Summary
The accident occurred during the final leg of a multi-stop flight from Appleton, Wisconsin, to Lincoln, Nebraska. As the aircraft approached its destination, it encountered a line of severe thunderstorms. To avoid turbulence, the crew requested and received clearances to lower altitudes, eventually descending toward 3,000 feet. During this descent, the aircraft entered a cell of extreme precipitation. The volume of water entering the engine intakes exceeded the flameout protection capabilities of the Garrett TPE331 engines, causing both to fail simultaneously. The NTSB investigation highlighted a breakdown in the weather information chain. Although meteorologists at the Minneapolis Air Route Traffic Control Center (ARTCC) were aware of the storm's severity and had issued warnings, this information was not passed down to the Omaha Radar Approach Control controllers or the flight crew. Furthermore, the aircraft's X-band weather radar suffered from attenuation, where heavy rain near the aircraft absorbed the radar pulses, preventing the crew from seeing the even more intense storm cells directly ahead. This 'radar shadowing' led the pilots to believe they were flying into moderate rain when they were actually entering a catastrophic weather system.
Final Conclusions
The NTSB determined the probable cause was the flight crew's continued flight into an area of severe thunderstorms, resulting in a precipitation-induced flameout of both engines at an altitude from which recovery could not be made. Contributing factors included the crew's failure to utilize all available weather sources, the air traffic control system's failure to disseminate critical weather information, and the limitations of X-band radar in heavy precipitation (attenuation). The final report, NTSB-AAR-80-15, was adopted on December 9, 1980.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Peter A. Grab, age 37.
First Officer
Nicholas Gallmeister, age 28.
Systems & Failure Modes
Garrett TPE331-3VW-303G Engines
Twin turboprop engines that suffered simultaneous flameouts due to massive water ingestion exceeding their design limits.
X-band Weather Radar
The onboard radar system suffered from attenuation, where heavy precipitation blocked the radar's ability to detect the core of the severe thunderstorm.
Interesting Facts
- 01One of the fatalities was Walter Rumsey, a survivor of the 1949 Mann Gulch fire.
- 02The aircraft's X-band radar was unable to penetrate the heavy rain, a phenomenon known as attenuation.
- 03Both engines were successfully relit before impact, but the aircraft had already lost too much altitude and control.
- 04The aircraft had a total of 8,055 airframe hours at the time of the accident.
- 05Severe storm warnings had been issued for the Omaha area but were not relayed to the flight crew by controllers.
- 06The aircraft's manufacturer serial number (MSN) was TC-228.
Safety Actions & Advisories
NTSB Safety Recommendation A-81-23
Issued to improve the dissemination of critical weather information within the ATC system to ensure pilots receive timely warnings of severe convective activity.