Investigation Summary
The accident occurred during a severe snowstorm that had closed Washington National Airport for snow removal. During the delay, Flight 90 underwent de-icing, but heavy snowfall continued. In an attempt to move from the gate, the crew used reverse thrust, which likely blew wet snow and slush onto the wings and into the engine probes. During the taxi, the crew followed a New York Air DC-9 closely, mistakenly believing the jet exhaust would melt ice on their wings; instead, it likely turned the snow into a slushy mixture that refroze. Crucially, the crew failed to activate the engine anti-ice system. This caused the Engine Pressure Ratio (EPR) probes to become blocked with ice, leading to false high thrust indications. When the First Officer set takeoff power based on these false readings, the engines were actually producing significantly less thrust than required for a safe departure. Despite the First Officer noting that the engine instruments 'didn't seem right' during the takeoff roll, the Captain elected to continue.
Final Conclusions
The NTSB determined the probable cause was the flight crew's failure to use engine anti-ice during ground operation and takeoff, their decision to take off with snow/ice on the airfoil surfaces, and the Captain's failure to reject the takeoff when abnormal engine instrument readings were noted. Contributing factors included the prolonged ground delay which allowed for ice accumulation and the crew's lack of experience in cold-weather operations.
Photographic Evidence (1)
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Crew Experience
Captain
Commercial jet experience logged at Air Florida.
First Officer
Experience as recorded in NTSB AAR-82-08.
Systems & Failure Modes
Engine Pressure Ratio (EPR) Probes
Sensors that measure the ratio of turbine discharge pressure to compressor inlet pressure to indicate engine thrust. Blockage by ice caused false high readings.
Engine Anti-Ice System
A system designed to prevent ice buildup on engine components and probes; it was left off by the crew despite freezing conditions.
Stick Shaker
A stall warning device that vibrates the control yoke; it activated almost immediately after liftoff.
Interesting Facts
- 01The aircraft struck seven occupied vehicles on the 14th Street Bridge, killing four motorists.
- 02Only five people on board (four passengers and one crew member) survived the crash and subsequent immersion in the icy river.
- 03Passenger Arland D. Williams Jr. famously passed the rescue lifeline to other survivors five times before drowning.
- 04The First Officer repeatedly questioned the engine instrument readings during the takeoff roll, stating 'that don't seem right,' but the Captain did not abort.
- 05The aircraft was 13 years old and had previously been operated by United Airlines.
Safety Actions & Advisories
De-icing Procedure Revisions
The accident led to stricter regulations regarding the timing of de-icing and the 'clean wing' concept, ensuring aircraft do not take off with any frozen contaminants.
CRM Training
The crash highlighted the need for better Cockpit Resource Management, specifically the need for Captains to listen to concerns raised by First Officers.