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ASN Wikibase Occurrence # 56849
Last updated: 12 December 2017
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Date:04-JAN-2009
Time:14:09
Type:Silhouette image of generic S76 model; specific model in this crash may look slightly different
Sikorsky S-76C
Owner/operator:PHI Inc
Registration: N748P
C/n / msn: 760629
Fatalities:Fatalities: 8 / Occupants: 9
Airplane damage: Written off (damaged beyond repair)
Category:Accident
Location:near Houma, Terrebonne Parish, LA -   United States of America
Phase: En route
Nature:Non Scheduled Passenger
Departure airport:Amelia, LA (7LS3)
Destination airport:Tambelier 301B, GM (301B)
Investigating agency: NTSB
Narrative:
A Sikorsky S-76C departed on an air taxi flight from PHI, Inc.ís heliport en route to an offshore oil platform with two pilots and seven passengers. Data from the helicopterís flight data recorder indicated that the helicopter established level cruise flight at 850 feet mean sea level and 135 knots indicated air speed. About 7 minutes after departure, the cockpit voice recorder recorded a loud bang, followed by sounds consistent with rushing wind and a power reduction on both engines and a decay of main rotor revolutions per minute. Due to the sudden power loss, the helicopter departed controlled flight and descended rapidly into marshy terrain.

Examination of the wreckage revealed that both the left and right sections of the cast acrylic windshield were shattered. Feathers and other bird remains were collected from the canopy and windshield at the initial point of impact and from other locations on the exterior of the helicopter. Laboratory analysis identified the remains as coming from a female red-tailed hawk; the females of that species have an average weight of 2.4 pounds. No defects in the materials, manufacturing, or construction were observed. There was no indication of any preexisting damage that caused the windshield to shatter. Thus, the fractures at the top of the right section of the windshield and damage to the canopy in that area were consistent with a bird impacting the canopy just above the top edge of the windshield. The fractures in the other areas of the windshields were caused by ground impact.

The S-76C helicopter has an overhead engine control quadrant that houses, among other components, two engine fire extinguisher T-handles and two engine power control levers (ECL). The fire extinguisher T-handles, which are located about 4 inches aft of the captainís and first officerís windshields, are normally in the full-forward position during flight, and each is held in place by a spring-loaded pin that rests in a detent; aft pulling force is required to move the T-handles out of their detents. If the T handles are moved aft, a mechanical cam on each T-handle pushes the trigger on the associated ECL out of its wedge-shaped stop, allowing the ECL to move aft, reducing fuel to the engine that the ECL controls. (Flight crews are trained to move an engineís fire extinguisher T-handle full aft in the event of an in-flight fire so that the ECL can move aft and shut off the fuel flow to the affected engine.)

The impact of the bird on the canopy just above the windshield near the engine control quadrant likely jarred the fire extinguisher T-handles out of their detents and moved them aft, pushing both ECL triggers out of their stops and allowing them to move aft and into or near the flight-idle position, reducing fuel to both engines. A similar incident occurred on November 13, 1999, in West Palm Beach, Florida, when a bird struck the windshield of an S-76C helicopter, N276TH, operated by Palm Beach County. The bird did not penetrate the laminated glass windshield, but the impact force of the bird cracked the windshield and dislodged the fire extinguisher T-handles out of their detents; however, in that case, the force was not great enough to move the ECLs.

Maintenance records indicated that PHI replaced the original laminated glass windshields delivered on the accident helicopter with after-market cast acrylic windshields about 2 years before the accident. The after-market windshields provided a weight savings over the original windshields. PHI again replaced the windshields (due to cracking) with cast acrylic windshields about 1 year before the accident. Aeronautical Accessories Incorporated (AAI) designed and produced the after-market windshields and obtained supplemental type certificate (STC) approval from the Federal Aviation Administration (FAA) in April 1997. AAI did not perform any bird-impact testing on the cast acrylic windshields supplied for the S-76C , and the FAAís approval of the STC did not require such testing.

PHI also replaced the original windshields on other helicopt
Probable Cause: (1) the sudden loss of power to both engines that resulted from impact with a bird (red-tailed hawk), which fractured the windshield and interfered with engine fuel controls, and (2) the subsequent disorientation of the flight crewmembers, which left them unable to recover from the loss of power. Contributing to the accident were (1) the lack of Federal Aviation Administration regulations and guidance, at the time the helicopter was certificated, requiring helicopter windshields to be resistant to bird strikes; (2) the lack of protections that would prevent the T handles from inadvertently dislodging out of their detents; and (3) the lack of a master warning light and audible system to alert the flight crew of a low-rotor-speed condition.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20090104X12037&key=1

Safety recommendations:

Safety recommendation A-10-136 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-137 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-138 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-139 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-140 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-141 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-142 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-143 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-144 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-145 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-146 issued 23 November 2010 by NTSB to FAA
Safety recommendation A-10-147 issued 23 November 2010 by NTSB to FAA


Revision history:

Date/timeContributorUpdates
04-Jan-2009 21:02 DavidLandry Added
04-Jan-2009 21:04 harro Updated
05-Jan-2009 09:07 robbreid Updated
11-Jun-2010 02:32 TB Updated [Operator, Location, Nature, Source, Narrative]
11-Jun-2010 03:06 TB Updated [Time, Aircraft type, Departure airport, Destination airport, Source, Narrative]
12-Jun-2010 12:29 TB Updated [Location, Source]
13-Jun-2010 13:44 TB Updated [Source, Narrative]
21-Sep-2014 14:07 Aerossurance Updated [Nature, Source, Narrative]
21-Dec-2016 19:25 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
01-Jan-2017 17:58 Aerossurance Updated [Time, Source, Embed code]
07-Jan-2017 14:59 Aerossurance Updated [Source, Narrative]
01-Dec-2017 11:38 ASN Update Bot Updated [Time, Aircraft type, Operator, Other fatalities, Departure airport, Destination airport, Source, Embed code, Narrative]

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