N813CE

History of Flight

On August 8, 1995, at 1545 hours Pacific daylight time, an Aerospatiale AS-355-F1, N813CE, entered ground resonance before lifting off a privately-owned helipad at Daggett, California, and sustained substantial damage. The pilot was beginning a visual flight rules business flight to John Wayne Airport, Santa Ana, California. The helicopter was registered to and operated by Southern California Edison (SCE), Ontario International Airport, Ontario, California. Neither the certificated airline transport pilot nor his passenger was injured. Visual meteorological conditions prevailed.

Preliminary examination revealed one of the arms (yellow) of the Starflex assembly was fractured between the elastomeric spherical bearing and its associated frequency adapter. The rotor mast assembly components were intact. The main rotor blades showed no evidence of any ground impact signatures. The transmission support tubes were intact and not buckled.

National Transportation Safety Board investigators interviewed the pilot on August 14, 1995, at the operator's flight operations/maintenance facility. The pilot said that he departed the operator's facility at 0640 hours and landed at John Wayne Airport about 0657 hours to pickup a passenger. The flight departed John Wayne Airport about 0700 hours and arrived at the operator's Coolwater Generating Station, Daggett, California, about 0750 hours and deplaned the passenger.

About 1540 hours, the passenger returned to the helipad and boarded. The pilot said that after starting the engines he let them idle for about 2 minutes until the gyroscopic flight instruments stabilized. He then applied power to begin the lift-off.

When the pilot felt the engines respond to the application of the power levers (the No. 2 engine was about 75 percent Ng and the No. 1 engine was slightly behind), the helicopter entered ground resonance. The helicopter began to turn, wobbling on each skid, about 45 degrees to the right and the pilot immediately shutdown both engines.

The pilot said that there was no advance warning of the resonance. Later he said that it appeared as if something in the rotor head broke. He also said that both previous landings and the entire flight were smooth.

The pilot described the winds as "light and variable (less that five knots)."

On January 31, 1996, the pilot said in a telephone interview that after starting the first engine he allowed the engine to remain in the idle position. He did not say that he advanced the fuel flow control lever to the "flight gate" position. He then started the second engine. The pilot said that the rotor speed during idle was about 290 rpm.

In a subsequent written statement (dated February 1, 1996), the pilot said that he started both engines while idling. He also said that this procedure was in accordance with the flight manual, whereas the engine(s) should be stabilized for 1 minute before advancing the fuel flow control lever to the flight gate position. He also said that the cyclic friction and the force trim mechanisms were engaged.

In a written statement, the passenger said that after boarding the helicopter, the pilot started both engines. The pilot then continued to ". . . perform additional operations on his control console. We were not yet ready to commence lift-off operations. . . ."

The passenger then stated:

Without any initiating event, we suddenly began to oscillate in a rhythmic fashion on the helipad. The oscillations started out quite small in amplitude, but began to build quite rapidly. As the oscillations built in intensity, we began to rotate slightly (clockwise) around the helipad.

Crew Information

The pilot holds an airline transport certificate with rotorcraft helicopter and AS-350 type ratings. The certificate is endorsed for commercial privileges with airplane ratings for single-engine land, multiengine land, instruments, and SK-61 type ratings. He also holds an unrestricted first-class medical certificate dated July 12, 1995.

The flight hours reflected on page 3 of this report were obtained from the pilot's company flight records. The records disclosed that the pilot accrued 12,242 total flight hours, of which 11,987 hours were flown in helicopters. The pilot also accrued 183 hours in the accident helicopter make and model.

The pilot satisfactorily completed a biennial flight review 17 months before the accident. A biennial flight review is required every 24-calendar months.

Aircraft Information

Safety Board investigators reviewed the helicopter's maintenance records at SCE maintenance facilities. The maintenance records' examination showed that SCE maintenance personnel accomplished the last annual inspection on February 16, 1995, and the last 100-hour inspection on June 1, 1995; the helicopter accrued 3,101 hours at the time of the 100-hour inspection. At the time of the accident, the helicopter accrued 3,170 hours (airframe and engines).

The maintenance records also revealed that the helicopter's previous owner installed the affected Starflex assembly on April 7, 1987; the assembly accrued 992.3 hours when it was installed.

On August 30, 1988, other maintenance personnel replaced all of the Starflex assembly sleeves.

At the time of the accident, the Starflex assembly accrued 2,177.6 hours. According to the manufacturer, the Starflex is a life-limited item and must be replaced when it accrues 2,200 operational hours.

On November 9, 1992, SCE maintenance personnel replaced the yellow Starflex sleeves; the helicopter accrued 2,500.6 hours.

On November 3, 1993, SCE maintenance personnel replaced the spherical thrust bearings and the red and blue sleeves.

On April 7, 1995, SCE maintenance personnel repaired the Starflex assembly according to the maintenance manual MRR repair card 62.20.00.601, Paragraph 3.1.3 (Temporary Repair). The maintenance manager told Safety Board investigators that the repairs were done in concert with the manufacturer's technical representative. The representative did not tell the mechanic that the full repair under MRR repair card 62.20.00.772 would have to be accomplished at a later time.

The mechanic told investigators that he contacted a manufacturer's technical representative before he started the repairs. He told the representative that the arms were splintered. The mechanic said he contacted the representative because he did not fully understand the explanation in the manual.

The representative then instructed the mechanic on how to repair the splintered arms. The representative said to blend the area on each side of the repaired area smoothly. He did not instruct the mechanic to remove the assembly and fully chamfer the entire affected arm.

The representative also told the mechanic that splintered arms were not uncommon and assured him that ". . . there has never been a Starflex failure. . . ."

During the helicopter examination the technical representative said that he instructed the mechanic on the repair procedure. The technical representative and an American Eurocopter engineer said the repairs were satisfactory.

Wreckage and Impact Information

The Safety Board did not conduct an on-scene investigation. The helicopter examination began on August 15, 1995.

Aircraft Examination:

The yellow arm of the Starflex assembly (serial No. M2060) fractured about 5 1/2 inches outboard of the elastomeric spherical bearing attach brackets; the red and blue arms were found intact. Visual examination of the fractured area showed adhesive separation.

The Starflex assembly yellow, red, and blue sleeves attach bolts were found tight. The lower side of the yellow arm upper sleeve displayed a single impact signature about 4.5 inches outboard of its vibration adapter assembly.

The Starflex assembly elastomeric bearings did not show any rubber material extrusions.

SCE maintenance personnel checked the forward and aft cross tube horizontal distance in accordance with the AS-350-F1 maintenance manual (32.13.00.601 page 1). The forward cross tube distance measured 76 inches and the rear cross tube distance measured 76.75 inches. According to the maintenance manual, the maximum allowable distance for the forward cross tube is 77.63 inches and 79.52 inches for the rear cross tube.

The deflection of the left spring blade, measured from the rear skid to the bottom of the blade, was 94 mm and the right spring blade was 88 mm. According to the maintenance manual, the distance should be greater than 85 mm.

The vibration device springs were numbered 414. The associated weight was a -21. The associated weight is required to be matched with the vibration device springs. According to the manufacturer, the numbered springs were properly matched with the associated weight. The weight weighs 929.7 grams. According to the overhaul manual, the minimum weight is 900 grams.

The left landing gear (skid) shock absorber measured about 9.2 inches between the attach clamp and the frame bulkhead; the right landing gear shock absorber measured 9.32 inches. According to the repair card, the distance should be 9.3 inches.

The main rotor swash plate rotated freely; no evidence of any binding was observed. The swash plate moved at 4.5 pounds tensionometer pull force. According to the maintenance manual, the maximum pull force is 5.6 pounds.

The main transmission mast chip detector was free of any metal particles.

Visual inspection of the vibration frequency absorbers showed no evidence of any laminate separations. (See AS-355-F1 maintenance manual 32.13.00.601, page 1.)

The main rotor mast did not display any vertical, lateral, or longitudinal looseness.

The main rotor blade pins did not display any abnormal wear patterns. The inner diameters of all of the blade attach bushings were 1.179 inches. According to the overhaul manual, the inner diameter limits are between 1.179 and 1.181...