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ASN Wikibase Occurrence # 150448
Last updated: 3 September 2019
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Date:12-JAN-2006
Time:03:43
Type:Silhouette image of generic B105 model; specific model in this crash may look slightly different
MBB Bo 105CBS-2
Owner/operator:Aviane Air Ambulance
Registration: N495LF
C/n / msn: S-645
Fatalities:Fatalities: 0 / Occupants: 4
Other fatalities:0
Aircraft damage: Written off (damaged beyond repair)
Location:Ponce -   Puerto Rico
Phase: Take off
Nature:Ambulance
Departure airport:Ponce, PR
Destination airport:San Juan, PR
Narrative:
After the patient was placed aboard the helicopter, the pilot started the engines and performed a hover check. He then moved the helicopter forward to gain airspeed and initiated a climb to cruise altitude. After reaching an altitude of about 100 feet, the main rotor rpm light and audio warning system activated, and the number 2 engine N1 rpm and torque began to decay. The pilot attempted to regain normal engine parameters, but was unable to regain engine rpm. The pilot maneuvered to avoid several light poles as he attempted to land in a parking lot. By this time, main rotor rpm had bled off sufficiently to prevent the hydraulic pumps from pressurizing the hydraulic system, and all flight controls locked is a slight right banked attitude. This prevented the helicopter from reaching the parking lot. The helicopter impacted a construction area in a right bank, nose down attitude. An on-site and later follow-up investigation by FAA and Rolls-Royce investigators revealed a B-nut on the Pc line connecting the power turbine governor (PTGOV) to the fuel control unit (FCU) had become loose at the T-fitting end. It was partially torqued and could be moved with the fingers. The female end was threaded onto the male end three-quarters of a turn. There was no cross-threading. The torque stripe was broken. According to Rolls-Royce Allison, "This line serves a critical function to the engine control system and when leakage occurs will cause the engine to roll back to an idle or near idle condition."
Probable Cause: A loose B-nut on the PC line connecting the power turbine governor (PTGOV) to the fuel control unit (FCU) that created a leak and caused the engine to roll back to an idle condition, causing a low hydraulic system pressure and subsequent control lock. A contributing factor was the unsuitable terrain (construction area) on which to make a forced landing.

Sources:

NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20060118X00085&key=1


Revision history:

Date/timeContributorUpdates
30-Oct-2012 04:32 TB Added
30-Oct-2012 04:38 TB Updated [Time, Total occupants, Location, Phase, Departure airport, Source, Narrative]
10-Oct-2016 17:29 TB Updated [Source]
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
05-Dec-2017 09:01 ASN Update Bot Updated [Cn, Other fatalities, Departure airport, Destination airport, Source, Narrative]
10-Dec-2018 18:45 TB Updated [Cn, Other fatalities, Damage]

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