Investigation Summary
While cruising at 8,000 meters (26,000 feet) at a speed of 630 km/h, the flight engineer accidentally moved the flap selector to the 40 degree extension. On the Ilyushin Il-18, this configuration at cruise speeds created massive drag and a severe nose-down pitching moment. The aircraft entered a steep dive, generating intense negative g-forces that pinned the crew away from the pedestal, making it physically impossible for them to retract the flaps. As the aircraft exceeded its structural limits during the descent, the flap assemblies were torn from the wings. The aircraft eventually struck the ground at a pitch angle of 107 degrees (past vertical), creating a crater up to 5 meters deep.
Final Conclusions
The investigation concluded that the primary cause was the accidental deployment of full flaps during level flight. A significant contributing factor was the design of the Il-18 flap selector, which lacked a mechanical lock or guard to prevent accidental movement. Unlike the earlier Ilyushin Il-14, the Il-18's controls were vulnerable to such errors, which proved catastrophic at high cruising speeds.
Video Analysis
No video analysis linked for this case file yet.
Airframe & Maintenance
Systems & Failure Modes
Flap Selector
The control lever used to extend or retract wing flaps, which lacked a safety guard to prevent accidental activation in flight.
Interesting Facts
- 01The aircraft impacted the ground at a pitch angle of 107 degrees, indicating it was slightly past vertical.
- 02The impact crater was measured at 3.5 to 5 meters deep.
- 03Aerodynamic forces were so great during the dive that the port and starboard flap assemblies were ripped from the wings.
- 04The debris field spanned approximately 300 to 350 meters in width.
Safety Actions & Advisories
Flap Selector Redesign
The investigation highlighted the lack of a protection mechanism on the Il-18 flap selector, leading to recommendations for mechanical locks similar to those found on the Il-14.