Investigation Summary
The mission, part of the Hurricane Energetics experiment, was intended to study the low-level environment of Hurricane Hugo, which was estimated to be a Category 3 storm. Due to a temporary failure of the belly radar, the crew lacked real-time high-resolution data on the storm's intensification. They entered the eyewall at 1,500 feet, significantly lower than the 5,000 feet typically recommended for major hurricanes. Upon entry, they encountered Category 5 winds and extreme vertical drafts. The violent motion caused 200-pound life rafts and cabin equipment to break loose, denting the ceiling. During this period, a sensor failure in the fuel control unit of the number 3 engine allowed an unregulated flow of fuel, leading to a massive engine fire. The pilots managed to shut down the engine and feather the propeller while battling severe downdrafts that brought the plane within 880 feet of the sea. Once inside the eye, the crew discovered the number 4 engine's deicing boot was peeling off, threatening the only other engine on the right wing. They dumped 15,000 pounds of fuel and scientific equipment to lighten the aircraft, eventually climbing to 5,000 feet where they were inspected by a U.S. Air Force C-130 (Teal 57). After the inspection, they continued their climb to 7,000 feet to exit the storm through a path scouted by Teal 57.
Final Conclusions
The NOAA investigation concluded that the primary cause of the engine fire was a failure of the sensor on the fuel control unit, which resulted in an over-rich fuel mixture. The extreme turbulence, while not the cause of the mechanical failure, exacerbated the emergency by forcing the aircraft into a dangerous dive and complicating recovery efforts. The investigation also identified the presence of mesovortices (small tornado-like features within the eyewall) which the crew could not detect in time due to the earlier radar malfunction and the low entry altitude.
Photographic Evidence (1)
Video Analysis
NOAA Hurricane Hunters: The Wildest Ride — Footage and interviews regarding the most turbulent flights in NOAA history, including the infamous 1989 encounter with Hurricane Hugo.
If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Fuel Control Unit (FCU)
A sensor failure within this unit allowed excessive fuel to flow into the number 3 engine, causing the fire.
Belly Radar
The primary weather radar used for storm structure analysis; its temporary failure prevented the crew from seeing the mesovortices in the eyewall.
Deicing Boot
The rubber boot on the number 4 engine began to detach during the incident, risking further engine damage if it had been ingested.
Interesting Facts
- 01The aircraft experienced extreme G-forces recorded between +5.8 g and -3.7 g, significantly exceeding its design limits.
- 02The crew dumped 15,000 pounds of fuel and ejected scientific equipment (bathythermograph probes) while circling in the eye to lighten the aircraft.
- 03The eyewall winds were measured at approximately 185-200 miles per hour, indicating Category 5 intensity.
- 04The eye of Hurricane Hugo was measured at approximately 9 to 12 miles across, requiring tight maneuvering while the aircraft was crippled.
- 05The aircraft was nicknamed 'Kermit' and 'The Princess', carrying the registration N42RF.
- 06The flight is recorded as the most turbulent mission in the history of NOAA's Hurricane Hunters.
Safety Actions & Advisories
Minimum Altitude Revision
NOAA implemented a mandatory minimum altitude of 5,000 feet for aircraft penetrating the eyewall of intense hurricanes.
Mission Review Protocols
New requirements were established for crews to conduct thorough mission reviews and weather updates immediately prior to eyewall penetration.