ASN Wikibase Occurrence # 36677
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| Date: | Monday 19 April 1993 |
| Time: | 15:52 |
| Type: |  Mitsubishi MU-2B-60 Marquise |
| Owner/operator: | South Dakota Department of Transportation |
| Registration: | N86SD |
| MSN: | 765SA |
| Year of manufacture: | 1979 |
| Total airframe hrs: | 4580 hours |
| Engine model: | GARRETT TPE-331-10 |
| Fatalities: | Fatalities: 8 / Occupants: 8 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | near Zwingle, Jackson County, Iowa -
 United States of America
|
| Phase: | Approach |
| Nature: | Executive |
| Departure airport: | Cincinnati Municipal Airport–Lunken Field, Cincinnati, Ohio (LUK/KLUK) |
| Pierre Regional Airport, Pierre, South Dakota (PIR/KPIR) | |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The aircraft was destroyed when it lost height and collided with a cattle feed silo during an instrument approach to
Dubuque Regional Airport (DBQ/KDBQ) eight miles southwest of Dubuque, a city in Dubuque County, Iowa. The accident happened in the late afternoon and in poor weather with a 300 foot overcast, 1.5 miles visibility in rain and wind 060 degrees at 20 knots. The aircraft came down near Zwingle, Jackson County, Iowa (at approximate co-ordinates 42°17′52″N, 90°41′13″W).
All eight person on board (crew of two plus six passengers) were killed. Among those killed in the crash was George Mickelson, Governor of South Dakota. The aircraft had been en route from Cincinnati, Ohio to Pierre, South Dakota, but the pilot had elected to divert to Dubuque due to a problem with the left engine and a loss of pressurisation.
It was subsequently determined that while cruising at FL 240, a propeller hub arm on the left propeller failed, releasing the propeller blade, which struck a 2nd blade, breaking off its tip. This resulted in a severe engine vibration and shutdown of the left engine. The left engine was forced downward and inboard on its mounts. The cabin de-pressurised, possibly from blade contact.
The aircraft was incapable of maintaining altitude and descended in instrument conditions. The left propeller hub failed from fatigue that initiated from multiple 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, de-carburisation, and residual stresses.
The NTSB determined the probable cause of the accident to be: 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 (de-carburisation, residual stress, corrosion, mixed micro
structure, and machining/scoring marks) that reduced the fatigue resistance of the material, probably combined with exposure to higher-thannormal cyclic loads during operation of the propeller at a critical vibration frequency (reactionless mode), which was not appropriately considered during the aircraft/propeller certification proces
Accident investigation:
 |
|
Sources:
1. NTSB Identification: DCA93GA042 at https://www.ntsb.gov/ntsb/brief.asp?ev_id=20001211X12106
2. FAA: http://registry.faa.gov/aircraftinquiry/NNum_Results.aspx?omni=Home-N-Number&nNumberTxt=86SD
3. http://www.ntsb.gov/investigations/AccidentReports/Reports/AAR9308.pdf
4. http://flightsafety.org/ap/ap_apr94.pdf
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 24-Oct-2008 10:30 | ASN archive | Added |
| 06-Mar-2016 18:57 | Dr.John Smith | Updated [Operator, Location, Nature, Departure airport, Destination airport, Source, Narrative] |
| 06-Mar-2016 18:58 | Dr.John Smith | Updated [Narrative] |
| 21-Dec-2016 19:23 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 05-Jun-2018 15:54 | mkulda | Updated [Narrative] |
| 15-Feb-2020 18:50 | harro | Updated [Source, Accident report, ] |
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