Investigation Summary
The flight was operating from Omaha to Denver when the crew detected a hydraulic failure. While the crew initially followed checklists for an abnormal situation and expected a routine landing, the situation escalated to a full emergency when hydraulic pressure dropped to zero during flap extension. The Douglas DC-8 touched down on Runway 26L, but when the crew moved the thrust levers to the reverse position, the reverser buckets for engines 1 and 2 (port side) failed to deploy. This resulted in the right-side engines generating reverse thrust while the left-side engines continued to produce forward thrust. The resulting massive asymmetrical thrust caused the aircraft to veer sharply to the right. The right main landing gear tires blew out under the lateral stress, and the aircraft departed the runway surface, entering a taxiway area that was under construction. The aircraft struck several pieces of heavy construction equipment and a surveyor's panel truck. The impact with the truck killed the driver on the ground and distorted the rear passenger loading door frame, rendering that exit inoperable from the inside. The nose gear collapsed, and a rupture in the right wing fuel tank ignited a massive fire. While many escaped, 16 passengers died from carbon monoxide inhalation, and one elderly passenger died from shock after breaking both ankles during the evacuation.
Final Conclusions
The Civil Aeronautics Board (CAB) determined the probable cause was the mechanical failure of the port side thrust reversers to deploy, combined with the crew's failure to recognize the malfunction in time to mitigate the asymmetrical thrust. Specifically, the First Officer failed to monitor the reverse thrust indicator lights when applying reverse power. The investigation also noted deficiencies in the airport fire department's emergency equipment, although the fire crews were commended for their rescue efforts under the circumstances.
Photographic Evidence (1)
Video Analysis
The Crash of United Airlines Flight 859 | Mini Air Crash Investigation — A detailed look at the 1961 landing accident in Denver involving a Douglas DC-8 that suffered a thrust reverser failure.
If playback is blocked, the owner has disabled embedding — use the link above.
Airframe & Maintenance
Crew Experience
Captain
Captain John Grosso
First Officer
First Officer Arthur F. Putz
Flight Engineer
Flight Engineer James M. Beatie
Systems & Failure Modes
Thrust Reversers
Mechanical buckets that redirect engine exhaust forward to slow the aircraft; on Flight 859, the port side buckets failed to deploy, creating asymmetrical thrust.
Hydraulic System
The aircraft suffered a hydraulic failure earlier in the flight, which necessitated the use of emergency procedures for landing gear and flap extension.
Reverse Thrust Indicator Lights
Cockpit lights intended to signal the successful deployment of reverser buckets; the First Officer failed to monitor these during the landing sequence.
Interesting Facts
- 01The aircraft was nearly brand new, having been manufactured only one month prior to the accident.
- 0216 of the 17 onboard fatalities were caused by carbon monoxide poisoning rather than impact trauma.
- 03The total death toll was 18, including one construction worker on the ground who was killed when the aircraft struck airport vehicles.
- 04The aircraft struck a taxiway that was actively under construction at the time of the landing.
- 05The port side engines (1 and 2) continued to provide forward thrust while the starboard engines (3 and 4) were in reverse.
Safety Actions & Advisories
Airport Fire Equipment Upgrade
Following findings that the airport fire department was deficient in emergency equipment, Stapleton International Airport and other major hubs reviewed and upgraded their crash tender capabilities.
FAA Airworthiness Directive: Hydraulic System
Source ↗The Federal Aviation Agency issued a mandatory Airworthiness Directive requiring extensive modifications to the Douglas DC-8 hydraulic system to prevent similar failures.
FAA Airworthiness Directive: Throttle Interlock
Source ↗A mandatory Airworthiness Directive was issued requiring all DC-8 aircraft to be equipped with a throttle thrust brake interlock to prevent the unintentional application of asymmetric reverse thrust.