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ASN Wikibase Occurrence # 153587
Last updated: 15 January 2022
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Type:Silhouette image of generic MD60 model; specific model in this crash may look slightly different
McDonnell Douglas MD 600N
Owner/operator:San Bernardino County Sheriff's Department
Registration: N625SB
MSN: RN033
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Location:Rialto, CA -   United States of America
Phase: Unknown
Departure airport:Rialto, CA (L67)
Destination airport:
Investigating agency: NTSB
The sheriffs department helicopter was just beginning an evening patrol flight when the engine experienced a deceleration event during transition from climb out to cruise and the helicopter crashed into a residential street during an attempted autorotation. First responders to the accident site, which included sheriff's air unit mechanics, found the engine running at idle and a fire in the engine compartment. The helicopter had just come out of a scheduled 100/300-hour inspection and this was the first mission flight since the maintenance. During the inspection, the engine's fuel control Hydromechanical Unit (HMU) had been removed for compliance with a service bulletin. Prior to this flight, the helicopter had completed a 10-minute post maintenance flight check. The pilot in command (PIC) conducted the preflight inspection. The mission observer flight officer, who held a private pilot certificate with helicopter rating and was attempting to upgrade to a pilot position, had been given permission to fly the helicopter and installed the dual flight controls to the right side. No problems were noted during the preflight, and the takeoff was normal. About 500 feet above ground level during the transition from climb out to cruise, the pilot flying heard the LOW ROTOR voice warning (two times) followed by ENGINE OUT voice warning (two times). Without initiating an autorotation, he requested that the PIC take the flight controls. Simultaneously, the PIC had sensed a problem and took the flight controls. Prior to and during the departure up until the engine deceleration, the PIC performed the observer flight officer duties, which included radio communications with dispatch, and had not monitored the flight instrument readings or the progress of the departure. The LOW ROTOR voice warning activates when Nr falls below 95 percent. The voice warning system for ENGINE OUT activates when N1 falls below 55 percent or a high rate of decay in N1. No discrepancies were noted during the inspection of the airframe. A teardown of the engine disclosed no internal discrepancies; however, the fuel inlet line fitting to the engine HMU was found loose by two flats of the nut. Functional testing of the fire damage ECU (electronic control unit) found no discrepancies. The HMU was installed in a test bench and passed a functional check. The fuel line inlet fitting nut was then loosened incrementally one flat at a time with a functional test conducted each time. Significant fluctuations in metered fuel output flow were noted during one test with the nut three flats loose, and again at one complete turn loose. These results could not be reliably duplicated in subsequent tests. The investigation found that the operator had not established guidance for crew resource management pertaining to crew responsibilities, instrument monitoring responsibilities, emergency procedures initiation, or flight control transfer procedures when flying in a dual pilot operation.
Probable Cause: an engine deceleration event due to a loose HMU fuel line fitting, which was a result of inadequate maintenance procedures in the 100/300-hour inspection. Also causal was the flying pilot's and pilot-in-command's delayed recognition of the power loss, as well as, the flying pilot's failure to initiate an autorotation in a timely manner. The pilot-in-command's failure to regain and maintain adequate main rotor rpm was also causal. A contributing factor to the accident was the pilot-in-command's inadequate supervision and diverted attention due to his concentration on the flight officer observer duties.




Revision history:

27-Feb-2013 10:14 TB Added
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
09-Dec-2017 17:54 ASN Update Bot Updated [Operator, Nature, Departure airport, Source, Narrative]

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