United Airlines Flight 553 - Crash

Crash

The accident occurred as the airplane was making its final approach to Midway Airport.

The plane was descending too fast, at too low an airspeed, to be within the required "stabilized approach" parameters. That situation was created by the fact that the plane was too fast and too high just prior to reaching the Kedzie Outer Marker Beacon (OMB), 3.3nmi prior to the threshold of runway 31L. The plane was 700 feet above the minimum crossing altitude when it passed over that OMB. The captain extended the spoilers (speed brakes) and steepened the descent.

When it emerged from cloud approximately 400-500' above the ground the airplane was descending at a rate of more than 1500ft/min. This compares to a descent rate of 600-700ft/min required by the precision approach path to runway 31L, and United Airlines' recommended descent rate for the Boeing 737 of 1000ft/min. The captain leveled the plane off, and increased engine power. However, the throttles were not advanced fully and, with the spoilers still extended, did not provide enough thrust to climb or even to maintain level flight without losing speed. The stick-shaker warning system activated 6-7 seconds after the aircraft leveled off and continued until it entered an aerodynamic stall.

It crashed into a house at 3722 W. 70th Place, 1.89 miles (3,043 meters) short of the runway.