Event Details

Title:In-flight loss of propeller blade and uncontrolled collision with terrain, Mitsubishi Mu-2B-60, N86SD, Zwingle, Iowa, April 19, 1993
Micro summary:This Mu-2B-60 experienced a catastrophic loss of a propeller, leading to a crash.
Event Time:1993-04-19 at 1552 CDT
File Name:1993-04-19-US.pdf
Publishing Agency:National Transportation Safety Board (NTSB)
Publishing Country:USA
Report number:NTSB-AAR-93-08
Site of event:Near Zwingle, Iowa
Latitude/Longitude:N4215'21.6" W9041'20.4"
Departure:Lunken Field, Cincinnati, Ohio, USA
Destination:Joe Foss Field Airport, Sioux Falls, South Dakota, USA
Airplane Type(s):Mitsubishi Mu-2B-60
Flight Phase:Cruise
Operator(s):South Dakota Department of Transportation
Type of flight:Revenue
Serious Injuries:0
Other Injuries:0
Executive Summary:On April 19, 1993, at 1552 central daylight time, a Mitsubishi MU-2B-60, registered in the United States as N86SD and operated by the South Dakota Department of Transportation, as a public use airplane, collided with a silo on a farm near Zwingle, Iowa, while attempting an approach to an emergency landing at Dubuque Regional Airport, Dubuque, Iowa. The airplane was destroyed in the collision and postcrash fire. The captain, first officer, and the six passengers aboard were fatally injured. Instrument meteorological conditions existed at the time. The flight originated from Cincinnati, Ohio, at 1406, on an instrument flight rules flight plan.

The National Transportation Safety Board determines that the probable cause of this accident was the fatigue cracking and fracture of the propeller hub arm. The resultant separation of the hub arm and the propeller blade damaged the engine, nacelle, wing, and fuselage, thereby causing significant degradation to aircraft performance and control that made a successful landing problematic.

The cause of the propeller hub arm fracture was a reduction in the fatigue strength of the material because of manufacturing and time-related factors (decarburization, residual stress, corrosion, mixed microstructure, and machining/scoring marks) that reduced the fatigue resistance of the material, probably combined with exposure to higher-than-normal cyclic loads during operation of the propeller at a critical vibration frequency (reactionless mode), which was not appropriately considered during the airplanelpropeller certification process.

The safety issues in this report include the propeller hub design, certification and continuing airworthiness, and air traffic control training. Safety recommendations concerning these issues were addressed to the Federal Aviation Administration.
Learning Keywords:Operations - Airspace - Air Traffic Control
Operations - Controlled Flight Into Terrain
Systems - Engine - Uncontained Engine Failure
Other - Certification
Other - Manufacturing Issues
Consequence - Damage - Airframe or fuselage
Consequence - Hull Loss


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