Individually Owned: 150,657
Corporate Owned: 137,281
Dubuque Regional Airport
Aircraft Accident/Incident Report
Zwingle, Iowa 52709
Monday, April 19, 1993 15:52 CDT
NTSB Narrative Summary Released at Completion of Accident
WHILE CRUISING AT FL 240, A PROPELLER (PROP) HUB ARM ON THE LEFT PROP FAILED, RELEASING THE PROP BLADE, WHICH STRUCK A 2ND BLADE, BREAKING OFF ITS TIP. THIS RESULTED IN A SEVERE ENGINE VIBRATION & SHUTDOWN OF THE LEFT ENGINE. THE LEFT ENGINE WAS FORCED DOWNWARD & INBOARD ON ITS MOUNTS. THE CABIN DEPRESSURIZED, POSSIBLY FROM BLADE CONTACT. THE FLIGHT CREW MADE AN EMERGENCY DESCENT & RECEIVED A VECTOR TO DIVERT FOR AN ILS APPROACH TO DUBUQUE. THE AIRPLANE WAS INCAPABLE OF MAINTAINING ALTITUDE & DESCENDED IN INSTRUMENT CONDITIONS. SUBSEQUENTLY, IT COLLIDED WITH A SILO & CRASHED ABOUT 8 MILES SOUTH OF DUBUQUE. AN INVESTIGATION REVEALED THE LEFT PROP HUB FAILED FROM FATIGUE THAT INITIATED FROM MULTIPLE INITIATION SITES ON THE INSIDE DIAMETER SURFACE OF THE HOLE FOR THE PILOT TUBE. THERE WAS EVIDENCE THAT THE FATIGUE PROPERTIES OF THE HUB WERE REDUCED BY A COMBINATION OF FACTORS, INCLUDING MACHINING MARKS OR SCRATCHES, MIXED MICRO- STRUCTURE, CORROSION, DECARBURIZATION, AND RESIDUAL STRESSES. (FOR FURTHER INFO, SEE BLUE COVER RPRT: NTSB/ARR-93/08.)
NTSB Probable Cause Narrative
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 AIRPLANE/PROPELLER CERTIFICATION PROCESS.
Event Information
| Type of Event | Accident |
| Event Date | 4/19/1993 |
| Event Day of the Week | Monday |
| Time of Event | 1552 |
| Event Time Zone | Central Daylight Time |
| Event City | ZWINGLE |
| Event State | IOWA |
| Event Country | -- |
| Zipcode of the event site | 52709 |
| Event Date Year | 1993 |
| Event Date Month | 4 |
| MidAir Collision Indicator | No |
| On Ground Collision occurred ? | No |
| Event Location Latitude | |
| Event Location Longitude | |
| Event Location Airport | DUBUQUE REGIONAL |
| Event Location Nearest Airport ID | DBQ |
| Indicates whether the acc/inc occurred off or on an airport | Off Airport/Airstrip |
| Distance from airport in statute miles | 8 |
| Degrees magnetic from airport | 180 |
| Airport Elevation | 1076 |
| Weather Briefing Completeness | Unknown |
| Investigator's weather source | Weather Observation Facility |
| Time of the weather observation | 1555 Central Daylight Time |
| Direction of event from weather observation facility (degrees) | 360 |
| Weather Observation Facility ID | DBQ |
| Elevation of weather observation facility | 1076 |
| Distance of event from weather observation facility (units?) | 9 |
| Time Zone of the weather observation | CDT |
| Lighting Conditions | Day |
| Lowest Ceiling Height | 200 |
| Lowest Non-Ceiling Height | 200 |
| Sky/Lowest/Cloud Conditions | Unknown |
| Sky Condition for Lowest Ceiling | Overcast |
| Visibility Runway Visual Range (Feet) | 0 |
| Visibility Runway Visual Value (Statute Miles) | 0 |
| Visibility (Statute Miles) | 1 |
| Air Temperature at event time (in degrees celsius) | 8 |
| Dew Point at event time (in degress fahrenheit) | 7 |
| Wind Direction (degrees magnetic) | 40 |
| Variable Wind Indicator | Unknown |
| Wind Speed (knots) | 16 |
| Wind Velocity Indicator | Unknown |
| Wind Gust Indicator | Not Gusting |
| Wind Gust (knots) | 0 |
| Altimeter Setting at event time (in. Hg) | 29.4 |
| Density Altitude (feet) | -- |
| Intensity of Precipitation | Light |
| METAR weather report | -- |
| Event Highest Injury | Fatal |
| On Ground, Fatal Injuries | 0 |
| On Ground, Minor Injuries | 0 |
| On Ground, Serious Injuries | 0 |
| Injury Total Fatal | 8 |
| Injury Total Minor | -- |
| Injury Total None | -- |
| Injury Total Serious | -- |
| Injury Total All | 8 |
| Investigating Agency | NTSB |
| NTSB Docket Number (internal use) | 205 |
| NTSB Notification Source | -- |
| NTSB Notification Date | Apr 19 1993 12:00AM |
| NTSB Notification Time | 2200 |
| Fiche Number and/or location -used to find docket information | 50003 |
| Date of most recent change to record | Dec 18 2002 11:38AM |
| User who most recently changed record | NTSB\GIUV |
| Basic weather conditions | Instrument Meteorological Cond |
| FAA District Office | -- |
Aircraft Involved |
|
|---|---|
Aircraft #1 |
|
| Aircraft Registration Number | N86SD |
| NTSB Number | DCA93GA042 |
| Missing Aircraft Indicator | N |
| Federal Aviation Reg. Part | Public Use |
| Type of Flight Plan filed | IFR |
| Flight plan Was Activated? | -- |
| Damage | Destroyed |
| Aircraft Fire | Ground |
| Aircraft Explosion | None |
| Aircraft Manufacturer's Full Name | MITSUBISHI |
| Aircraft Model | MU-2B-60 |
| Aircraft Series Identifier | MU-2B-60 |
| Aircraft Serial Number | 765 S.A. |
| Certified Max Gross Weight | 11575 |
| Aircraft Category | Airplane |
| Aircraft Registration Class | U.S. Registered/U.S. Soil |
| Aircraft is a homebuilt? | No |
| Flight Crew Seats | -- |
| Cabin Crew Seats | -- |
| Passenger Seats | -- |
| Total number of seats on the aircraft | 10 |
| Number of Engines | 2 |
| Fixed gear or retractable gear | Retractable |
| Aircraft, Type of Last Inspection | Continuous Airworthiness |
| Date of Last Inspection | Apr 12 1993 12:00AM |
| Airframe hours since last inspection | 10 |
| Airframe Hours | 4580 |
| ELT Installed | Unknown |
| ELT Activated | Unknown |
| ELT Aided Location of Event Site | Unknown |
| ELT Type | -- |
| Aircraft Owner Name | STATE OF SOUTH DAKOTA |
| Aircraft Owner Street Address | 700 EAST BROADWAY |
| Aircraft Owner City | PIERRE |
| Aircraft Owner State | SD |
| Aircraft Owner Country | |
| Aircraft Owner Zipcode | 57501 |
| Operator is an individual? | -- |
| Operator Name | |
| Operator Same as Owner? | Yes |
| Operator Is Doing Business As | -- |
| Operator Address Same as Owner? | Yes |
| Operator Street Address | |
| Operator City | |
| Operator State | |
| Operator Country | |
| Operator Zip code | |
| Operator Code | |
| Owner has at least one certificate | None |
| Other Operator of large aircraft? | No |
| Certified for Part 133 or 137 Operation | Unknown |
| Operator Certificate Number | -- |
| Indicates whether an air carrier operation was scheduled or not | Unknown |
| Indicates Domestic or International Flight | Unknown |
| Operator carrying Pax/Cargo/Mail | Unknown |
| Type of Flying (Per_Bus / Primary) | Public Use |
| Second Pilot on Board | Yes |
| Departure Point Same as Event | No |
| Departure Airport Code | LUK |
| Departure City | CINCINNATI |
| Departure State | OH |
| Departure Country | |
| Departure Time | 1400 |
| Departure Time Zone | EDT |
| Destination Same as Local Flt | -- |
| Destination Airport Code | PIR |
| Destination City | PIERRE |
| Destination State | SD |
| Destination Country | |
| Specific Phase of Flight | Approach |
| Report sent to ICAO? | -- |
| Evacuation occurred | -- |
| Date of most recent change to record | Oct 22 2001 3:26PM |
| User who most recently changed record | dbo |
| Since inspection or accident | -- |
| Event Location Runway Number and Location | 31 |
| Runway Length | 6498 |
| Runway Width | 150 |
| Sight Seeing flight | No |
| Air Medical Flight | No |
| Medical Flight | -- |