Wind Shear Overview

     On July 2, 1994, at 6:43 PM, a plane collided with trees and a private residence near the Charlotte/Douglas International Airport. The crew and 14 passengers sustained serious injuries; 37 passengers died.

     The flight originated in Columbia, where the weather information provided to the crew indicated that conditions at Charlotte were similar to those encountered when they had departed an hour earlier. The flight was routine until the plane was on final approach to Charlotte. During approach, the officer commented that there was more rain than he had expected. They observed on the airborne weather radar two "cells," the first located to the south and the second east of the airport. They then noticed that one of the cells moved right onto the runway. They made contingency plans to bail out to the right in case they would need to do a missed approach and remarked that there was a chance of windshear. The captain asked for a report from the last pilot to land, whom the controller said reported a "smooth ride all the way down the final." They then heard an air traffic controller issue a takeoff clearance to another USAir departing flight along with the information that "aircraft just departed ahead of you said smooth ride on departure." The captain received and acknowledged two transmissions about the wind conditions and told the officer to "stay heads up." The captain then commented "here comes the wipers," followed 3 seconds later by the sound of rain. The first officer commented "there’s, ooh, ten knots right there" and the captain said "OK, you’re plus twenty [knots] take it around go to the right," meaning that the weather conditions were adverse enough to warrant aborting the landing and coming around again. In accordance with the procedure, the first officer raised the flap handle. While the wing flaps were retracting, the airplane encountered a severe windshear at an altitude of 275 feet, causing it to drop "like riding a roller coaster."

     An on-board windshear alert system did not detect the severe windshear conditions during the go-around because it was programmed not to work while the flaps retract in order to reduce nuisance alarms. During the design of the alert system, the system was simulated with many different types of windshear profiles and flap settings, but not in the case where flaps are in transition. Therefore, the nuisance alarms were not discovered until the system was used in operations.

     Pilots are trained to be sensitive to windshear conditions in simulators. Several pilots have characterized the windshear profiles used in the simulator training as readily identifiable because it always happens during the initial takeoff or final approach phase of flight, and that all of the profiles were preceded by turbulence, unlike in this case.