A Meteorological Analysis of the American Airlines Flight 1420 Accident

Late in the day on June 1, 1999, an American Airlines flight (AAL 1420) arriving at Little Rock, AR from Dallas-Fort Worth, TX was involved in a fatal accident upon landing on runway 4R at Adams Field (LIT). There were eleven casualties, including the pilot, and numerous injuries among the 145 passengers and crew on board. At the time of the accident, 0451 UTC (11:51 PM CDT), severe thunderstorms existed in the vicinity of the airport. These storms were sparked by an approaching cold front and pre-frontal trough and were developmentally aided by veering low-level wind and warm air advection, which helped to further destabilize the atmosphere. This report will focus on the meteorological conditions preceding and immediately following the accident that could have played a contributing role in the crash. However, no theories on the actual cause will be put forth.

Data from a variety of meteorological sources will be considered herein. Initially, the surface observations as reported by the National Weather Service's Automated Surface Observing System (ASOS) will be presented. The second section will focus on expert analysis of the reflectivity and velocity base data obtained from the National Weather Service's Next Generation Weather Radar (NEXRAD), located in North Little Rock, AR (KLZK). Finally, surface wind data, as recorded by the six-sensor Low-Level Wind Shear Alert System (LLWAS), will aid in the depiction of the actual wind conditions at the surface and will also corroborate the information presented by the ASOS and NEXRAD sensors. In addition to these data sources, National Track Analysis Program (NTAP) beacon data (courtesy of the National Transportation Safety Board) for AAL 1420 was used to determine the position of the aircraft in time and space relative to both the airport and thunderstorms.

Many of the high-profile aircraft accidents involving less-than-desirable weather conditions are attributed to a phenomenon called the microburst. This form of low-level wind shear has been given enough publicity that pilots are generally well informed and trained on the consequences of flying into such an event. However, there can be other weather-related causes of near-ground aircraft accidents besides the wind shear and microbursts, including excessive crosswind and heavy precipitation. It is hoped that the information presented will serve as a reminder to those in the aviation community that underestimating the effects of weather on an airborne aircraft can and does have serious consequences, especially in the critical phases of take-off and landing.