Ryan International Airlines Flight 590

Investigation

Less than an hour after the accident occurred, the NTSB was notified about it. A go-team traveled to Cleveland four hours later. The United States Postal Service and airport workers recovered mail that had not been destroyed in the crash.

The left wing and number-one (left) engine were both destroyed during the accident sequence, but the right wing and number-two (right) engine, were mainly intact. The number-one engine had a high rotation speed at the time of impact. The flaps were extended to 20° at the time of impact, though the flap handle (part of it having been bent on impact) was positioned near 30°. The horizontal stabilizer was at 34° nose up. The engine anti-ice heat switches were in the "ON" position at the time of impact. Despite witnesses stating that the aircraft was on fire or exploded before impact, the only fire and explosions had occurred during the impact sequence.

According to the CVR, the most notable information was during the takeoff sequence, including captain Reay's callouts, as well as the stick shaker and engine compressor stalls. According to the flight data recorder (FDR), the aircraft had reached a maximum airspeed of 155 kn during its flight. The stick shaker had activated at 150 kn. Flight 590 had experienced a sudden drop in normal acceleration to 0.7 g during its takeoff. The NTSB compared the takeoff of Flight 590 with another DC-9-10 in similar conditions. The acceleration of the comparison flights only dropped to almost 0.9 g during takeoff.

The NTSB examined other accidents that were involved icing, such as Ozark Air Lines Flight 982, Air Florida Flight 90, and Continental Airlines Flight 1713. Following the Flight 1713 accident, McDonnell Douglas presented a paper warning about ice accumulation on DC-9s. The FAA had also disagreed with a safety recommendation from the Flight 1713 accident (labeled as A-88-134), which recommended DC-9-10 series aircraft be de-iced with strong glycol during icing conditions.

Ryan International Airlines' DC-9s flight crew operations manual (FCOM) required the first officer to inspect the aircraft for ice after landing in icing conditions. However, according to ground witnesses, neither crew member left the aircraft while it was parked. The NTSB believed that this was because of the flight crew's previous experience with larger variants of the DC-9, which have leading edge devices and are less vulnerable to icing conditions, and possibly the fact that no other flight requested deicing before takeoff. The NTSB even considered fatigue as a reason the crew did not inspect the aircraft (as well as if it was a factor in the accident altogether), the crew had been on the same flight schedule on the same route for six days and captain Reay may have been experiencing a cold; the demanding schedules can hamper illness recovery and contribute to fatigue. Nevertheless, the NTSB had insufficient evidence and was unable to determine if fatigue did indeed play a role in the accident.

The NTSB also noted that both Douglas and the FAA had been aware of previous DC-9 accidents in icing conditions, but had poor oversight. Ryan International Airlines was also unaware of these accidents when they purchased the DC-9s.

Conclusion

The NTSB published its final report nearly nine months later, stating:

The NTSB determined that the accident had been caused by the icing contamination as a result of the flight crew failing to conduct an external examination of the aircraft after landing in cold weather, as well as the failure of the FAA, McDonnell Douglas, and Ryan International Airlines to respond appropriately from previous ice-related accidents, and their lack of understanding of icing condition of the DC-9-10 aircraft.

Six safety recommendations were issued to the FAA, and recommendation A-88-134 was reiterated.