Incident
Before takeoff, the crew of United Airlines Flight 663 (registration N7647U) observed cumulus clouds and virga in the area. At approximately 1327, a DeHavilland Dash 7 crew reported a 25-knot loss of airspeed, however several other aircraft subsequently took off without reporting any issues. Due to radio congestion, the captain did not query other aircrews but decided to climb out at V2 plus 20 knots.
When the air traffic controller cleared Flight 663 for takeoff, he advised the crew of numerous wind shears in three quadrants but used incorrect terminology when issuing the wind shear alert. During the takeoff roll, the aircraft struck an ILS localizer antenna located 1,074 feet from the departure end of the runway, damaging the lower fuselage. After becoming unable to pressurize the aircraft, the crew returned to the airport and landed safely.
Investigation
An investigation revealed that the aircraft encountered wind shear from microburst activity, which reached its greatest intensity as Flight 663 was taking off. The wind sheared from an 8-knot headwind to 40 to 56 knots over a 44-second period. The crew noted a hesitation while accelerating through 120 knots, then at or beyond the rotation speed (Vr) of approximately 141 knots, the aircraft momentarily lost 20 knots of indicated airspeed.