What happened
On July 11, 1961, a United Air Lines DC-8, registered as N8040U, experienced a series of mechanical issues during its flight from Omaha, Nebraska, to Denver, Colorado. Following takeoff from Omaha, the crew encountered hydraulic difficulties. Adhering to established emergency procedures for abnormal hydraulic conditions, the crew proceeded toward Stapleton Airfield.
As the aircraft approached Denver, the crew attempted to extend the flaps to 25 degrees. This action caused the hydraulic pressure to drop to zero. In response, the crew adjusted the hydraulic system selector to the No. 3 position to maintain the gear and flap downlock status and continued the approach for landing.
Upon touchdown on the runway, the crew engaged the reverse thrust by moving the throttles to the idle reverse position. Immediately after applying power, the aircraft veered uncontrollably from the runway. The plane subsequently struck a panel truck, causing fatal injuries to the truck driver. While none of the 122 occupants sustained severe injuries from the initial impact, 16 passenger fatalities occurred due to carbon monoxide poisoning during the ensuing fire. Additionally, one passenger died later from shock following ankle fractures sustained during the evacuation.
Findings
Investigations into the accident determined that the primary cause was asymmetric thrust caused by the failure of the thrust reversers on engines 1 and 2 when reverse power was applied during the hydraulic emergency. A secondary factor involved the failure of the first officer to properly monitor the thrust reverse indicator lights at the moment reverse thrust was engaged.