History of Flight
On July 4, 2008, at approximately 0030 Pacific daylight time, a Schweizer 269C-1 helicopter, registration N2011A, collided with transmission wires over the Sinclair Freeway (Interstate 680) in Sunol, California. The helicopter was consumed by fire and destroyed. Operated by Silicon Valley Helicopters under 14 Code of Federal Regulations Part 91, the flight was a night cross-country training mission. The certified flight instructor (CFI) and the pilot undergoing instruction (PUI) were killed.
The flight originated from Byron Airport, Byron, California, around 1130 on July 3, destined for Reid-Hillview Airport in San Jose. Visual meteorological conditions prevailed, and no flight plan was filed. Earlier, the pilots had flown from San Jose to Stockton Metropolitan Airport, then to Byron for refueling. The CFI telephoned his spouse indicating he would arrive back in San Jose in 45 minutes.
Witness Account
A witness driving southbound on I-680 observed a small helicopter ahead. The fog was low, and the helicopter remained below the clouds. The helicopter's ground speed decreased, prompting the witness to slow to about 50 mph, suspecting an emergency. The witness then exited the freeway, watching the helicopter increase speed and altitude. Re-entering the freeway, he saw the helicopter drift south as the road grade increased. An explosion occurred as the helicopter contacted transmission wires crossing the interstate. The helicopter came to rest on a street adjacent to the freeway and erupted into flames.
Personnel Information
The CFI, aged 27, held a commercial pilot certificate with rotorcraft and instrument ratings (issued January 2006) and a flight instructor certificate with rotorcraft and instrument ratings (issued April 2006). He held a second-class medical certificate issued June 2007 with no limitations. His logbook recorded 588.8 total hours, all in rotorcraft, mostly in the same make/model. He had about 264 hours as a flight instructor and was hired by the operator in June 2007. A former check pilot recalled flying with the CFI 14-15 months earlier and pointing out high power lines crossing the interstate, noting they were difficult to see and had caused accidents.
The PUI, aged 39, held a private pilot certificate with rotorcraft-helicopter rating (issued May 2007) and a CFI for airplane single and multiengine land and instrument. He had 1,496.1 total hours, including 85.2 in rotorcraft and 670.3 as a fixed-wing CFI. He and the CFI had flown together on two prior occasions totaling 1.4 hours in the accident helicopter, last on April 18, 2008.
Aircraft Information
The Schweizer 269C-1, serial number 0016, was manufactured in 1995. The airframe had about 644 total hours. The most recent annual inspection was completed July 20, 2007. The Lycoming HO-360-C1A engine, serial number L6420-36A, was installed in October 2004; its last annual inspection was March 4, 2008, at 1,233.6 hours.
Meteorological Conditions
A METAR at 0053 from Livermore Municipal Airport (11 miles northeast) reported clear skies, visibility 10 statute miles, wind from 280° at 10 knots, temperature 59°F, dew point 55°F, altimeter 29.96 inHg. An FAA inspector arriving about 3 hours after the accident noted low fog; he could not discern the transmission towers or wires and estimated the cloud layer at about 200 feet AGL. He used windshield wipers due to moisture.
Wreckage and Impact
The accident site was in a small canyon about 3.5 miles long, oriented east-west. I-680, an eight-lane highway, runs through the canyon. Elevation at the site was about 655 feet MSL; surrounding hills about 800 feet MSL. The main wreckage (fuselage and engine) came to rest on Sheridan Road, perpendicular to the interstate. Power lines were adjacent, with four major support structures (unlit) on each side of the interstate; the tallest was 120 feet AGL. The wires crossed the interstate at a near 45° angle, with colored balls on the highest wires. These were the only wires crossing the interstate in that canyon.
The post-impact fire spread to hilly areas east of I-680, burning about 6.1 acres. Approximately 750 customers lost power until about 03:40. The helicopter sustained thermal damage except for the main rotor head, tail boom, and tail rotor. The FAA inspector noted markings indicating the helicopter contacted a high-tension wire, severing it. Two high-tension towers east of the site carried three and six wires, respectively.
Medical and Pathological
Autopsies were performed on both pilots by the Alameda County coroner. Toxicology testing on the CFI was negative for ethanol.
Tests and Research
A Safety Board investigator examined the wreckage on July 23, 2008, at Plain Parts in Pleasant Grove, California. The wreckage had extensive thermal damage. Examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.
A Garmin GPSMAP 496 portable GPS receiver was found in the wreckage. Recorded data plots from 22:50:12 to 22:28:59 showed the flight track from Stockton to Byron, then southwest to I-680, following the interstate at altitudes between 300 and 700 feet MSL and speeds of 30-50 mph. The last four hits (23 seconds) showed speed slowing from 31 to 24 mph then unknown, altitudes: 704, 712, 756, 685 feet MSL. Direction changed from 227° true to 133° true.
Additional Information
The San Francisco VFR Terminal Area Chart (72nd edition, March 18, 2008) depicted the tower and power lines crossing the interstate in the accident area.