N90230

HISTORY OF FLIGHT

On March 23, 1998, about 0740 hours Pacific standard time, a Bell 205A-1, N90230, owned by the City of Los Angeles, California, and operated by the Los Angeles City Fire Department (LAFD), experienced the separation of its tail rotor blades and the 90-degree gearbox during cruise flight. A forced landing was initiated, and during the autorotative descent the helicopter collided with trees approximately 1.5 statute miles northwest of its destination, Children's Hospital in Los Angeles, California. The purpose of the flight was to provide air ambulance transportation for a seriously injured passenger. Visual meteorological conditions prevailed, and the LAFD was monitoring the helicopter's flight progress. The public-use helicopter was operated under the provisions of Title 14 CFR Part 91. The helicopter was destroyed upon impacting the terrain, and the commercial certificated pilot and one crewmember were seriously injured. Three additional crewmembers and the passenger sustained fatal injuries. The local area flight originated from the Van Nuys Airport, California, about 0722.

Upon dispatch, the helicopter flew about 7 miles northeast and landed about 0731 at the Stonehurst Elementary School playground, near the scene of an automobile traffic accident. At this location, the trauma patient (passenger) was loaded into the helicopter. The pilot took off about 0733.

Using the air traffic control call sign "Lifeguard Fire Three," the pilot flew in a south-southeasterly direction past the Burbank Airport while climbing and leveling off between 1,900 and 2,100 feet mean sea level (msl). Recorded radar track data indicates that the helicopter attained a 104-knot average ground speed.

Between 0737:17 and 0737:22, while cruising over a heavily wooded mountainous area known as Griffith Park, an event occurred which was manifested by an increase in the helicopter's average ground speed to about 118 knots. Seconds later, between 0737:26 and 0737:45, the helicopter's average speed reduced to between 76 and 84 knots, while descending through its last recorded altitude of 1,400 feet msl.

Thereafter, three other pilots and two ground witnesses reported hearing radio transmissions about a helicopter in an emergency or going down in Griffith Park. About 0739 one of these pilots, who was communicating with the Burbank Air Traffic Control Tower, reported hearing an emergency transmission about a helicopter crashing. About 0740, two news media helicopter pilots reported hearing a call from Fire Three that he was experiencing an emergency over Griffith Park. This transmission was followed 20 seconds later with the statement "gonna put it in Griffith Park." Two air support police officers, who were in hangars, heard the following transmissions at 0740: "Fire 3 we have an emergency."

During this approximate time, two hikers were on a mountain trail in Griffith Park. They reported hearing two "bangs" and observing components depart the southerly flying helicopter as it passed west of the Griffith Park Planetarium. Additional witnesses reported seeing the helicopter descend down a canyon and collide with a series of trees before crashing in a partial clearing.

INJURIES TO PERSONS

Two of the six persons onboard the helicopter survived. No one on the ground was injured.

PERSONNEL INFORMATION

Air Operations Unit Management, Duties & Responsibilities.

The Air Operations Unit (AOU) of the LAFD is headed by a commander (manager) who, on a daily basis, is physically located at the airport unit. The commander reports to superior personnel located in the department's downtown Los Angeles headquarters.

In brief, the commander is responsible for helicopter operations including planning, scheduling of training, maintaining records, implementing department orders and communicating with his headquarters management. The commander does not possess a pilot certificate.

The AOU is staffed on a 24-hour basis with LAFD helicopter pilots. According to the AOU commander, the pilots are responsible for the safety of the helicopter in which they are flying. They are in command of the helicopter, and have the authority to veto any proposed operation, which in the pilot's opinion, would be unsafe. (See the extract from the Air Operations Manual for the statement of pilot responsibility.)

Flight Crewmembers.

On the accident flight, the helicopter crewmembers consisted of one pilot, two helitacs and two paramedics. The helitacs are trained to serve as helicopter crewmembers. In part, they are responsible for overseeing the safety of the working environment including providing guidance to ground personnel. The paramedics perform emergency medical aid to the patient, if required.

Pilot.

A review of the pilot's personal flight record logbook indicates that he began primary flight training in July 1990, and he received a private pilot certificate in November, 1990, with an airplane single engine land rating. In June 1993, he began rotorcraft flight training, and 4 months later he was issued a commercial pilot certificate. The pilot subsequently was issued a certified flight instructor certificate with rotorcraft privileges.

In October 1995, after principally training in the Robinson R22 and the Bell 206 helicopters, the pilot received his first flight in the Bell 205A-1 (accident) helicopter. The pilot continued receiving LAFD flight training in the helicopter, and the following year he completed the checkout process.

By the accident date, the pilot had approximately 1,865 total flight hours, of which about 1,440 hours were flown in rotorcraft. His total experience piloting the Bell 205A-1 helicopter, and his experience flying this model during the 90-day period preceding the accident, were 234 and 15 hours, respectively.

Between 1997 and 1998, the pilot received refresher training in emergency procedures including touchdown autorotations and tail rotor failures. On August 4, 1997, the pilot passed an Federal Aviation Administration (FAA) administered proficiency flight check evaluating his knowledge and skill as an air carrier (FAR Part 135) pilot.

AIRCRAFT INFORMATION

Certification and Operations Base.

The FAA issued the newly manufactured transport category helicopter, serial number 30221, a standard airworthiness certificate on March 12, 1976. On May 10, 1976, the FAA registered the helicopter in the name of the City of Los Angeles.

The helicopter was physically based at the LAFD's Van Nuys Airport Air Operations Unit, which is adjacent to the Los Angeles City Helicopter Operations and Maintenance Facility. The Los Angeles City Director of General Services and maintenance facility management reported that the helicopter was maintained in accordance with FAA regulations including Bell's service bulletins.

Helicopter Modifications and Utilization.

The Los Angeles City maintenance participant reported that the helicopter's interior had never undergone a major modification or overhaul. An external, belly-mounted, water tank had been installed on the bottom of the helicopter.

According to the LAFD, the helicopter was principally used for fire-fighting (water drops) and other activities such as flight and swift water rescue training. Secondarily, it was used as an air ambulance, although it had not been configured with any equipment for such usage. During the accident flight, emergency medical equipment for the care of the patient that the LAFD had required, by policy, to be onboard was not carried. (See the L.A. County Prehospital Care Policy Manual for the list of required equipment absent from helicopter.)

Tail Rotor Design and Yoke Straightness.

The Bell Helicopter participant reported that the company had designed the tail rotor assembly of the helicopter with two tail rotor blades. The blades are bolted to a yoke that holds them together. The yoke assembly is mounted onto the output drive shaft of the tail rotor's 90-degree gearbox, which rotates the yoke. The yoke is referred to as a flex-beam yoke. A portion of the yoke is referred to as the "flexure." This portion accommodates movement or flapping of the tail rotor blades during in-flight rotation.

Additionally, the yoke can flex under certain ground operations, and when exposed to adverse environmental conditions. Bell personnel verbally reported to the National Transportation Safety Board investigator during a March 26, 1998, telephone conference, that when bending loads are applied to the yoke which exceed its design strength, its relative "straightness" may be altered, and the yoke's anticipated infinite service life will be reduced.

Bell Helicopter initially placed a retirement life limit of 4,000 hours on the yoke. Bell personnel further reported that following a review of the service history and fatigue evaluation data for this model yoke, and with FAA approval, the yoke's retirement life was increased to 5,000 hours. This action occurred in October 1989.

Alert Service Bulletin.

Bell issued an Alert Service Bulletin (ASB), number 205-96-68, dated August 1, 1996, which was pertinent to the yokes installed in all model 205A-1 helicopters between serial number 30001 and 30228, having a time since new greater than zero hours. In summary, Bell indicated that if the yoke encountered adverse bending loads during specific ground handling or in-flight conditions, it could flex and become deformed. Bell provided the following description of events about which it was concerned:

"...When not turning, the tail rotor yoke flexure is susceptible to static overload if it is loaded by external bending forces. Examples of bending loads include high wind gusts (such as those from prop blast), improper ground handling (where the tail rotor blade has been used as a hand hold), improper feathering bearing removal (where the yoke assembly is not properly supported when pressing out bearings), or a ...