N397E

HISTORY OF FLIGHT

On May 3, 2004, at 2345 Pacific daylight time, a Bell OH-58A+, N397E, struck a power line during an autorotation to a residential street near Bakersfield Junior College, Bakersfield, California. The loss of engine power preceded the autorotation. The Kern County Sheriff's Department (KCSD) operated the helicopter as a routine patrol mission, as a public-use flight under the provisions of 14 CFR Part 91. The flying pilot (FP), a commercial helicopter rated pilot, and the commercial helicopter rated tactical flight officer (TFO) were not injured. Visual meteorological conditions prevailed for the local area surveillance flight, and a company visual flight rules (VFR) flight plan had been filed. The flight departed Meadow's Field Airport (BFL), Bakersfield, about 2226. The flight was scheduled to terminate at BFL.

The National Transportation Safety Board investigator-in-charge (IIC) interviewed both pilots. According to the pilots, the first flight of the night lasted 2 hours, with no discrepancies encountered. They indicated that after the first flight, they refueled the helicopter; however, during the refueling the fuel truck ran dry. The pilots indicated that 20 gallons of fuel had been pumped onboard the helicopter. While the deputies were on break, the operator refilled the fuel truck, and prior to the accident flight an additional 24 gallons of fuel was pumped onboard the helicopter.

The accident occurred about 1 hour 15 minutes into the second flight. The pilots received a call regarding a stolen car about 2 miles from their current position. The FP made a 180-degree turn to respond to the call. Halfway through the turn, both pilots heard a "big boom" and the helicopter shuddered. The FP leveled the helicopter and assessed the situation. He made a decision to land in a nearby parking lot. About 30 seconds later while they were en route to the parking lot, the pilots heard another loud boom followed by the engine out audio and warning lights.

PILOT STATEMENTS

Pilot-in-command/Flying Pilot (FP)

According to the FP's written statement to the Safety Board, he reported that they departed BFL about 2226 as Air One. About 2345, Air One was in the vicinity of Alfred Harrell Highway, west of Fairfax when they were requested to respond to a possible carjacking in the Oildale area. He noted their altitude at 1,100 feet mean sea level (msl), with an airspeed of 60 knots, prior to adding power. The pilot added power (about 80 percent torque) and initiated a right turn towards the west while accelerating to about 80 knots.

During the turn both he and the tactical flight officer (TFO) heard a loud boom and felt a vibration in the helicopter. The FP immediately reduced the power by lowering the collective, and reduced the airspeed to about 60 knots. They discussed the cause of the noise and were in the process of deciding to land or return to BFL when they heard a second loud boom followed immediately by a loss of engine power. The FP lowered the collective and entered into an autorotation.

The southwest parking lot of Bakersfield College was in front of them, and had been chosen as their primary emergency landing zone prior to the loss of engine power. While maneuvering to land, the FP recognized that he was going to overshoot the landing zone (LZ). He initiated a flare, but decided to continue over flying the LZ, while maintaining his airspeed. The TFO suggested Haley Street for landing. The FP made a turn northbound and lined up with Haley Street. About 60 to 75 feet above the ground the FP initiated the flare for landing. During the flare, they felt a "strong jolt" and an increased rate of descent. The FP reported noticing a loss of rotor rpm (revolutions per minute).

The FP maintained a level attitude, and about 10 feet above the ground he applied full collective pitch, and the helicopter landed hard with very little forward airspeed. After they secured and exited the helicopter, they realized that the helicopter had clipped power lines.

Tactical Flight Officer (TFO)

According to the TFO's written statement to the Safety Board, he reported that they received a call to respond to a possible carjacking about 2 miles to the west of their location. The TFO noted that during the turn to respond to the call, the pilot added power. While still in the turn he heard a loud boom and felt a vibration in the helicopter. At first he thought they had hit a bird and they were discussing the situation and their options when the heard a second loud boom, followed by a loss of engine power.

The TFO reported that during the first loud boom he noted the engine oil pressure gage and N1 gage were in the normal range. He further noted that the time between the two booms was between 30 seconds to a minute. When the engine quit, the TFO heard the engine out audio warning through his helmet and saw both the red and yellow caution warning lights illuminate on the instrument panel. At that point he turned his attention outside the helicopter to aid the FP in finding a suitable landing spot.

PERSONNEL INFORMATION

Pilot in Command/Flying Pilot

According to KCSD, the pilot was hired on August 22, 1977, and assigned to the Aviation Division on July 16, 1988. The pilots' most recent quarterly check ride, conducted by KCSD, was completed on March 10, 2004.

A review of Federal Aviation Administration (FAA) airman records revealed the FP held a commercial helicopter certificate.

The pilot held a second-class medical certificate issued on June 26, 2003. It contained the limitation that the pilot must wear corrective lenses.

According to NTSB Form 6120.1/2, Pilot/Operator Aircraft Accident Report, the pilot reported accumulating a total flight time of 5,773.4 hours, with a total flight time of 548 hours in the accident make and model helicopter. He logged 91.3 hours in the last 90 days, with 36.6 hours in the accident make and model. He logged 34.9 hours in the last 30 days, of which 28.3 hours were in the accident make and model. The FP logged 3.6 hours in the accident make and model in the last 24 hours.

Tactical Flight Officer

According to KCSD, the pilot was hired on November 28, 1984, and assigned to the Aviation Division on April 1, 1995. The pilot's most recent quarterly check ride, conducted by KCSD, was completed on March 9, 2004.

A review of Federal Aviation Administration (FAA) airman records revealed the TFO held a commercial helicopter certificate.

The pilot held a second-class medical certificate issued on August 8, 2003. It contained no limitations or waivers.

According to NTSB Form 6120.1/2 Pilot/Operator Aircraft Accident Report, the pilot reported accumulating a total flight time of 2,821.2 hours, with a total time of 765 hours in the accident make and model helicopter. He logged 99.2 hours in the last 90 days, and 46 hours in the accident make and model. He logged 30.5 hours in the last 30 days, of which 8.7 hours were in the accident make and model. The TFO logged 4.5 hours in the accident make and model in the past 24 hours.

AIRCRAFT INFORMATION

Airframe

The helicopter was a Bell OH-58A+, serial number 70-15442. A review of the helicopter's logbooks revealed a total airframe time of 6,667.1 hours at the last 100-hour inspection. The last 100-hour inspection was completed on April 13, 2004. An annual (Phase) inspection was completed on February 25, 2004, at an aircraft total time of 6,499.4 hours.

Engine

A Rolls-Royce/Allison, model 250-C20B, serial number CAE 835723 engine, was installed on the helicopter. Total time on the engine at the last 100-hour inspection on April 13, 2004 was 8,787.2 hours.

Acro Aerospace, Inc., Richmond, British Columbia, Canada, conducted a 1,750-hour inspection of the engine, which was completed on December 30, 2003. As a result of the inspection the second stage gas producer turbine nozzle diaphragm was replaced by machining out the old diaphragm and brazing in a new diaphragm. The engine then ran for an additional 161.7 hours before the accident.

According to the flight crew, at the time of departure (2230), the helicopter had a total of 88 gallons of Jet A fuel prior to the accident flight. Examination of the maintenance and flight department records revealed no unresolved maintenance discrepancies against the helicopter prior to departure.

The Rolls-Royce/Allison 250-C20B is a two-shaft turboshaft engine with a combination compressor, which consists of a six-stage axial compressor attached to a one-stage centrifugal compressor. The engine incorporates a reverse-flow annual combustor, a two-stage high-pressure turbine (also referred to as the N1, gas producer turbine), and a two-stage low-pressure turbine (also referred to as the N2 power turbine). The gas path along the Rolls-Royce/Allison 250 engine flows into the inlet, through the compressor's axial and centrifugal stages, into two external air transfer tubes and to the combustor, which is located at the very rear of the engine. The gases then turn 180 degrees toward the front of the engine and proceed through the two-stage gas producer turbine (N1) and a two-stage power turbine (N2). Finally, the gases are directed out of the exhaust collector and upward through two exhaust outlets.

The gas producer (GP) turbine, consisting of turbine wheels and nozzles #1 and #2, drives the compressor section of the engine through an inner shaft, while the power turbine (PT), consisting of turbine wheels and nozzles #3 and #4, drives the power output gear (to the main rotor transmission) and the accessory gearbox through an outer shaft. The inner shaft rotates independently within the outer shaft.

TESTS AND RESEARCH

Tests

The Safety Board investigator and representatives from Rolls-Royce/Allison engines and Kern County Sheriff's Department, who were parties to the investigation, examined the helicopter and engine at the Kern C...