Fuel exhaustion Accident Sikorsky S-61N N805AR, Tuesday 6 September 2016
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Date:Tuesday 6 September 2016
Time:13:40
Type:Silhouette image of generic S61 model; specific model in this crash may look slightly different    
Sikorsky S-61N
Owner/operator:AAR Airlift Group
Registration: N805AR
MSN: 61717
Year of manufacture:1974
Total airframe hrs:40296 hours
Engine model:GE CT58-140-2
Fatalities:Fatalities: 3 / Occupants: 3
Other fatalities:0
Aircraft damage: Destroyed
Category:Accident
Location:Palm Bay, FL -   United States of America
Phase: Manoeuvring (airshow, firefighting, ag.ops.)
Nature:Test
Departure airport:Melbourne International Airport, FL (MLB/KMLB)
Destination airport:Melbourne International Airport, FL (MLB/KMLB)
Investigating agency: NTSB
Confidence Rating: Accident investigation report completed and information captured
Narrative:
The helicopter flight crew, consisting of a pilot, copilot, and maintenance crewmember, was performing 20-knot rearward flight about 200 ft above ground level as part of a post-maintenance functional check flight (FCF). While the pilot was flying and recovering from the first rearward flight maneuver, unusual sounds were heard, which the flight crew identified as a compressor stall. The pilot then told the maintenance crewmember that they were returning to their home airport; however, after discussing compressor stalls and engine exhaust gas temperatures with the copilot, the pilot changed his mind and told the maintenance crewmember that they were going to try the maneuver again in a different direction relative to the wind (with the wind off the nose). While the pilot was recovering from the second rearward flight maneuver, there was a change in background noise, which the maintenance crewmember identified as a compressor stall. About 2 seconds later, there was another change in background noise, consistent with a decay in drivetrain rpm, which was followed by the helicopter descending and impacting the ground.

Although the crew identified the sounds and loss of power as compressor stalls, a sound spectrum study could not characterize the gas generator speed (Ng) behavior, due to overdriven audio on the CVR, to determine the engine anomaly the crew identified as a compressor stall. It is likely that the cause of the overdriven audio is related to an engine anomaly. At the same time the engine anomaly occurred, the sound spectrum revealed Nr quickly decayed due to a dual loss of engine power coupled with a high collective setting. Because main rotor speed (Nr) decayed at the same time the overdriven audio occurred, it is likely both engines lost power nearly simultaneously. No anomalous damage to the engines was found that would have explained the dual loss of engine power and the main rotor drive system did not exhibit evidence of preimpact mechanical malfunction. Fuel exhaustion was unlikely given the estimated fuel load at the time of the accident. After the overdriven audio, the rate of Ng decay for each engine appeared similar to engine Ng decay when at a lower power setting. Due to a lack of a flight data recorder or a cockpit image recorder, the behavior of the engines as well as the position of the cockpit engine control levers at the time of the anomaly could not be determined.

- Probable Cause:
A dual loss of engine power for undetermined reasons after the pilot's improper decision to attempt another maneuver after recovering from a perceived compressor stall, rather than returning to the airport.

Accident investigation:
cover
  
Investigating agency: NTSB
Report number: ERA16FA311
Status: Investigation completed
Duration: 2 years and 6 months
Download report: Final report

Sources:

NTSB
http://aerossurance.com/helicopters/aar-fatal-s61n-dual-power-loss/

Location

Images:


Photo: NTSB

Media:

Revision history:

Date/timeContributorUpdates
06-Sep-2016 22:04 Aerossurance Added
06-Sep-2016 22:05 Aerossurance Updated [Country, Damage, ]
06-Sep-2016 22:06 Aerossurance Updated [Phase, Departure airport, Narrative, ]
06-Sep-2016 22:09 Aerossurance Updated [Registration, Cn, Operator, Source, Embed code, ]
06-Sep-2016 22:13 Aerossurance Updated [Embed code, Narrative, ]
06-Sep-2016 22:16 Aerossurance Updated [Embed code, ]
07-Sep-2016 10:50 Iceman 29 Updated [Embed code, ]
08-Sep-2016 11:02 CTYONE Updated [Operator, Total occupants, Nature, Source, ]
08-Sep-2016 13:52 Aerossurance Updated [Source, Narrative, ]
08-Sep-2016 21:20 Aerossurance Updated [Source, Narrative, ]
11-Sep-2016 16:05 Aerossurance Updated [Time, Source, Embed code, ]
11-Sep-2016 16:09 Aerossurance Updated [Source, Embed code, ]
11-Sep-2016 16:24 Aerossurance Updated [Other fatalities, Phase, Destination airport, Narrative, ]
14-Sep-2016 10:46 Aerossurance Updated [Time, Source, Narrative, ]
08-Mar-2019 16:02 Aerossurance Updated [Embed code, ]
08-Mar-2019 16:04 Aerossurance Updated [Source, Embed code, Narrative, ]
08-Mar-2019 19:56 ASN Update Bot Updated [Time, Operator, Nature, Departure airport, Destination airport, Source, Embed code, Narrative, Accident report, ]
08-Mar-2019 20:00 harro Updated [Nature, Departure airport, Destination airport, Embed code, Narrative, Photo, ]
18-Jun-2020 18:50 Aerossurance Updated [Operator, Source, ]
17-Mar-2021 00:50 Captain Adam Updated [Narrative, ]

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