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ASN Wikibase Occurrence # 144491
Last updated: 6 October 2019
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Date:16-MAR-2012
Time:10:15
Type:Silhouette image of generic C172 model; specific model in this crash may look slightly different
Cessna 172K Skyhawk
Owner/operator:Skywarrior Inc
Registration: N79509
C/n / msn: 17258140
Fatalities:Fatalities: 0 / Occupants: 2
Aircraft damage: Substantial
Category:Accident
Location:Gulf Breeze, Pensacola Bay, FL -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Nature:Training
Departure airport:Pensacola, FL (PNS)
Destination airport:Pensacola, FL (PNS)
Investigating agency: NTSB
Narrative:
During the training flight, the single-engine airplane was in cruise flight about 1,000 feet above ground level when the engine stopped operating. The flight instructor assumed control of the airplane and unsuccessfully attempted to restart the engine while descending for an emergency landing. He ditched the airplane into a nearby bay. The airplane sustained substantial damage to the windshield during the accident sequence and was submerged in salt water. Postaccident examination of the engine revealed that the bolt or lockplate, which attaches the crankshaft gear to the aft end of the crankshaft, was missing. Further, the alignment dowel was fractured across about one-third of the cross-sectional area. The bolt and lockplate were likely either not installed or were improperly installed, which would allow the bolt to loosen and become disengaged. Measurements of the dowel, pilot flange, and counterbore recess diameters were all within the manufacturer's specifications; the dowel also met the manufacturer's hardness requirement. Because the components were within manufacturer's specifications, it is likely that the components did not have any preexisting wear or manufacturing issues. Additionally, wear marks on the crankshaft, dowel, and gear were likely caused by the newly installed gear and were consistent with either no installation or improper installation of the bolt or lockplate. Therefore, it is likely that when the wear on the dowel had proceeded through about one-third of the cross-section, the stresses in the dowel became sufficiently high to initiate fatigue cracks at the base of the worn part of the dowel and eventually led to a fatigue fracture. The evidence is consistent with the failure of maintenance personnel to install, or properly install, the bolt and lockplate during the engine’s last overhaul, which resulted in the crankshaft gear becoming separated from the crankshaft and a total loss of engine power. If the engine had failed at a point that would have allowed the pilot to land the airplane on land, the airplane damage is less likely to have been substantial; therefore, contributing to the accident was the lack of suitable terrain.

Probable Cause: A total loss of engine power due to the improper installation of the crankshaft gear bolt or lockplate by maintenance personnel. Contributing to the accident was the lack of suitable terrain for a forced landing.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20120320X73601&key=1
http://www.nwfdailynews.com/articles/rosa-48237-santa-county.html
[LINK NOT WORKING ANYMORE:http://www.fox10tv.com/dpp/news/local_news/santa_rosa/small-plane-crashes-in-hickory-shores]
https://www.faa.gov/data_research/accident_incident/preliminary_data/events01/media/03_79509.txt
https://www.skywarriorinc.com/index.php?option=com_content&task=view&id=16&Itemid=27_
https://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20120320X73601&key=1
https://flightaware.com/photos/view/38276-7d3e75fc4896f8a93f203221f12032d8227dd66f/all/sort/votes/page/5140


Images:


Taken in Turner Maine, about 1971 or 72.

Revision history:

Date/timeContributorUpdates
19-Mar-2012 15:53 Geno Added
19-Mar-2012 16:04 Geno Updated [Narrative]
21-Mar-2012 23:42 RobertMB Updated [Aircraft type]
27-Mar-2012 21:52 Geno Updated [Time, Location, Source, Damage, Narrative]
21-Dec-2016 19:26 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
27-Nov-2017 20:25 ASN Update Bot Updated [Other fatalities, Departure airport, Destination airport, Source, Narrative]
30-Jul-2018 17:34 pabobfin Updated [Date, Source, Photo, ]

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