Event Details

Title:Loss of directional control, Western Air Lines, Inc., Boeing 720-047B, N3166, Ontario International Airport, Ontario, California, March 31, 1971
Micro summary:This Boeing 720-047B rolled and yawed to the right while executing a simulated missed approach with the #4 engine inoperative.
Event Time:1971-03-31 at 0633:29 PST
File Name:1971-03-31-US.pdf
Publishing Agency:National Transportation Safety Board (NTSB)
Publishing Country:USA
Report number:NTSB-AAR-72-18
Site of event:3140' west of approach end and 420' north of centerline of RWY 25
Latitude/Longitude:N3403', W11736'
Departure:Ontario International Airport, Ontario, California, USA
Destination:Ontario International Airport, Ontario, California, USA
Airplane Type(s):Boeing 720-047B
Flight Phase:Missed Approach
Operator(s):Western Air Lines
Type of flight:Revenue
Serious Injuries:0
Other Injuries:0
Executive Summary:A Western Air Lines, Inc., Boeing 720-047B, N3166, operating as Flight 366, crashed on the Ontario International Airport, Ontario, California, at 0633:29 Pacific standard time, on March 31, 1971. All five crewmembers, the only occupants of the aircraft, were fatally injured. The aircraft was completely destroyed by impact and ensuing fire.

Flight 366, a routine proficiency check flight, was executing an Instrument Landing System approach to Runway 25 at Ontario with the No. 4 engine reduced to idle power to simulate an engine-out approach. The flight had been cleared to land or to execute a missed-approach procedure at the pilot-in-command'sdiscretion. At decision height, approximately 100 feet above the runway, a simulated engine-out missed approach procedure was initiated. The aircraft began to climb and the landing gear was retracted. The aircraft continued to climb to an altitude of about 500 feet above the runway while rotating to the right about its roll and yaw axes. As the rotation continued, the nose of the aircraft descended to a near-vertical downward position, and the aircraft crashed on a southeasterly heading approximately 3,140 feet west of the approach end and 420 feet north of the centerline of Runway 25.

The weather at Ontario about 3 minutes after the accident was: 600 feet overcast, 3/4-mile visibility in fog, haze and smoke, wind from 250' at 4 knots, and a Runway 25 visual range of more than 6,000 feet. Similar conditions were reported 34 minutes prior to the accident, except the ceiling and visibility were 500 feet and 518-mile, respectively.

Investigation revealed that the rudder hydraulic actuator support fitting had failed, resulting in the complete loss of left rudder control shortly after commencement of the missedapproach. The fitting failed due to a combination of stress-corrosion cracking and high tensile loading.

The National Transportation Safety Board determines that the probable cause of this accident was the failure of the aircraft rudder hydraulic actuator support fitting. The failure of the fitting resulted in the inapparent loss of left rudder control which, under the conditions of this flight, precluded the pilot's ability to maintain directional control during a simulated engine-out missed-approach. The existing weather conditions degraded external visual cues, thereby hampering rapid assessment of aircraft performance by the flight check captain.
Learning Keywords:Operations - Training Flight
Operations - Uncontrolled Flight into Terrain
Systems - Flight Control System
Systems - Hydraulics
Consequence - Hull Loss


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