Flight 470 Gulf of Mexico Accident (N90893)

Flight Operations and Weather Reports Flight 470 departed Tampa at 1543 local time, following a flight plan filed in Miami for a direct route to New Orleans at 14,500 feet under Instrument Flight Rules. The estimated elapsed time for the 498 statute mile journey was two hours. Weather data attached to the captain's flight plan included a forecast of thunderstorms with moderate to severe turbulence near New Orleans. Air Route Traffic Control cleared the flight at 14,500 feet direct to the destination. At 1614, Flight 470 passed over the NA-3 checkpoint at its cruising altitude and reported to Radio-Tampa, estimating it would pass over NA-2 at 1642. The flight reported local weather as broken clouds at 6,000 feet and 20,000 feet, with a temperature of 4 degrees Celsius. ## Turbulence Advisories Meanwhile, Flight 917 landed at New Orleans at 1612. At 1624, its captain sent a message to Miami Flight Control and company stations between New Orleans and Jacksonville, Florida, including Pensacola, advising of extreme turbulence at all altitudes just east of New Orleans. A follow-up message at 1636 referenced severe turbulence from checkpoint NA-1 to New Orleans, noting that weather appeared better to the west of the city. At 1649, Flight 470 reported passing over NA-2 at 1645 at 14,500 feet and estimated being over NA-1 at 1710. The flight also reported thunderstorms in all quadrants. Pensacola radio acknowledged this and advised the flight of severe turbulence between NA-1 and New Orleans, as reported by Flight 917. When Flight 470 asked what altitude the turbulence was reported at, it was informed of severe turbulence at all altitudes. ## Descent and Loss of Contact At 1654, Flight 470 advised Pensacola that it was reducing power due to turbulence. Five minutes later, it requested clearance to descend from 14,500 feet to 4,500 feet, which was granted with the provision that the descent between 10,000 and 8,000 feet be visual. At 1703, the flight advised passing through 10,000 feet, and at 1712 (recorded), it reported reaching 4,500 feet at 1710. Pensacola repeated this message and provided the 1648 New Orleans special weather report: measured ceiling 800 feet, overcast, visibility 10 miles, wind north-northeast 25 mph with gusts to 34 mph, altimeter 29.61, and barometer unsteady. After the flight acknowledged, there were no further radio contacts. An attempt by New Orleans at 1718 to contact Flight 470 was unsuccessful, as were subsequent attempts by several other stations. At 1840, the Coast Guard's air-sea rescue service was alerted. Low clouds and heavy seas hampered the search by air and sea. ## Recovery and Findings On the following day, February 15, floating debris and 17 bodies were recovered from a localized area in the Gulf of Mexico at approximately 30 degrees 38' North Latitude and 87 degrees 46' West Longitude. This position was about 38 miles to the right of the aircraft's direct course and approximately 20 miles southeast of Mobile Point at the easterly mouth of Mobile Bay. Two wristwatches on recovered bodies were impact-stopped at 1710 local time. ## Probable Cause The Board determined that the probable cause was the loss of control followed by in-flight failure and separation of portions of the airframe structure while the aircraft was traversing an intense frontal-wave type storm of extremely severe turbulence. The severity and location of the storm had not been fully communicated to the pilot. Findings noted that the flight reported thunderstorms in all quadrants after passing NA-2, requested and was granted clearance to descend to 4,500 feet due to turbulence, and its last message reported reaching 4,500 feet at 1710 local time. The aircraft penetrated a storm system of unusual severity, with tornadic conditions including high winds, violent gusts, and possible waterspouts. The storm's movement had not been adequately anticipated in current weather forecasts. Although a special Severe Weather Bulletin issued at Washington, D.C., was received by National Airlines and the Weather Bureau at Miami and New Orleans, no U.S. Weather Bureau advisory weather reports were issued to Air Route Traffic Control to report the unexpected development and movement of the storm to en route flights, and National Airlines did not attempt to relay this information to Flight 470. The aircraft's structure failed at a moment when gust loads combined with violent maneuvering loads were likely being imposed to maintain or regain control. The main wreckage was located in the Gulf of Mexico 3.8 miles offshore and about 52 miles to the right of course, with the left wing found 2,100 feet from the main wreckage. Examination of recovered parts revealed no indication of malfunctioning controls, fatigue failure, fire, explosion, or lightning strike while in flight.