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ASN Wikibase Occurrence # 58935
Last updated: 28 July 2020
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Time:09:56 LT
Type:Silhouette image of generic S92 model; specific model in this crash may look slightly different
Sikorsky S-92A
Owner/operator:Cougar Helicopters
Registration: C-GZCH
C/n / msn: 920048
Fatalities:Fatalities: 17 / Occupants: 18
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Location:Atlantic, 35 mi E off St John's, NL -   Canada
Phase: En route
Nature:Passenger - Non-Scheduled/charter/Air Taxi
Departure airport:St John's IAP (CYYT)
Destination airport:Hibernia platform Sea Rose FPSO
On 12 March 2009, at 09:17 Newfoundland and Labrador daylight time, a Cougar Helicopters' Sikorsky S-92A, operated as Cougar 91 (CHI91), departed St. John's International Airport, Newfoundland and Labrador, with 16 passengers and 2 flight crew, to the Hibernia oil production platform. At approximately 09:45, 13 minutes after levelling off at a flight-planned altitude of 9000 feet above sea level (asl), a main gearbox oil pressure warning light illuminated. The helicopter was about 54 nautical miles from the St. John's International Airport.
The flight crew declared an emergency, began a descent, and diverted back towards St. John's. The crew descended to, and levelled off at, 800 feet asl on a heading of 293 Magnetic with an airspeed of 133 knots. At 09:55, approximately 35 nautical miles from St. John's, the crew reported that they were ditching. Less than 1 minute later, the helicopter struck the water in a slight right-bank, nose-high attitude, with low speed and a high rate of descent.
The fuselage was severely compromised and sank quickly in 169 metres of water. One passenger survived with serious injuries and was rescued approximately 1 hour and 20 minutes after the accident. The other 17 occupants of the helicopter died of drowning. There were no signals detected from either the emergency locator transmitter or the personal locator beacons worn by the occupants of the helicopter.

Findings as to Causes and Contributing Factors:

1. Galling on a titanium attachment stud holding the filter bowl assembly to the main gearbox (MGB) prevented the correct preload from being applied during installation. This condition was exacerbated by the number of oil filter replacements and the re-use of the original nuts.
2. Titanium alloy oil filter bowl mounting studs had been used successfully in previous Sikorsky helicopter designs; in the S-92A, however, the number of unexpected oil filter changes resulted in excessive galling.
3. Reduced preload led to an increase of the cyclic load experienced by one of the titanium MGB oil filter bowl assembly attachment studs during operation of CHI91, and to fatigue cracking of the stud, which then developed in a second stud due to increased loading resulting from the initial stud failure. The two studs broke in cruise flight resulting in a sudden loss of oil in the MGB.
4. Following the Australian occurrence, Sikorsky and the Federal Aviation Administration (FAA) relied on new maintenance procedures to mitigate the risk of failure of damaged mounting studs on the MGB filter bowl assembly and did not require their immediate replacement.
5. Cougar Helicopters did not effectively implement the mandatory maintenance procedures in Aircraft Maintenance Manual (AMM) Revision 13 and, therefore, damaged studs on the filter bowl assembly were not detected or replaced.
6. Ten minutes after the red MGB OIL PRES warning, the loss of lubricant caused a catastrophic failure of the tail take-off pinion, which resulted in the loss of drive to the tail rotor shafts.
7. The S-92A rotorcraft flight manual (RFM) MGB oil system failure procedure was ambiguous and lacked clearly defined symptoms of either a massive loss of MGB oil or a single MGB oil pump failure. This ambiguity contributed to the flight crew's misdiagnosis that a faulty oil pump or sensor was the source of the problem.
8. The pilots misdiagnosed the emergency due to a lack of understanding of the MGB oil system and an over-reliance on prevalent expectations that a loss of oil would result in an increase in oil temperature. This led the pilots to incorrectly rely on MGB oil temperature as a secondary indication of an impending MGB failure.
9. By the time that the crew of CHI91 had established that MGB oil pressure of less than 5 psi warranted a "land immediately" condition, the captain had dismissed ditching in the absence of other compelling indications such as unusual noises or vibrations.
10. The captain's decision to carry out pilot flying (PF) duties, as well as several pilot not flying (PNF)

In addition to a TSB investigation the accident lead to a Public Inquiry under Mr Justice Wells commissioned by the Canada-Newfoundland & Labrador Offshore Petroleum Board, which reported in Nov 2010 and Aug 2011.

Following the accident a series of rulemaking activity has been underway to clarify the certification requirements.


Safety recommendations:

Safety recommendation A11-01 issued 29 December 2010 by TSB to FAA
Safety recommendation A11-02 issued 29 December 2010 by TSB to FAA
Safety recommendation A11-03 issued 29 December 2010 by TSB to Transport Canada
Safety recommendation A11-04 issued 29 December 2010 by TSB to Transport Canada

Revision history:

12-Mar-2009 10:26 angels one five Added
12-Mar-2009 10:33 harro Updated
12-Mar-2009 11:04 angels one five Updated
12-Mar-2009 22:02 stjohnsperson Updated
13-Mar-2009 04:02 morethanwords Updated
13-Mar-2009 05:29 stjohnsguy Updated
13-Mar-2009 08:01 Anon. Updated
13-Mar-2009 11:47 harro Updated
03-Mar-2010 23:26 TB Updated [Time, Location, Departure airport, Destination airport, Source, Damage, Narrative]
04-Mar-2010 02:19 TB Updated [Location, Departure airport, Source]
15-Feb-2011 14:06 harro Updated [Time, Location, Departure airport, Source, Narrative]
15-Feb-2011 14:06 harro Updated [Departure airport, Narrative]
15-Feb-2011 14:06 harro Updated [Departure airport, Narrative]
15-Feb-2011 14:06 harro Updated [Departure airport, Narrative]
15-Feb-2011 14:06 harro Updated [Departure airport, Narrative]
15-Feb-2011 14:07 harro Updated [Departure airport, Narrative]
25-Feb-2013 02:44 TB Updated [Location, Source, Narrative]
03-Aug-2014 18:24 Aerossurance Updated [Source, Narrative]
08-May-2016 15:05 Aerossurance Updated [Time, Location, Nature]
04-Aug-2016 07:23 Aerossurance Updated [Source]
06-Mar-2020 17:29 Anon. Updated [Embed code]

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