NTSB Identification: ERA10MA188
14 CFR Part 91: General Aviation
Accident occurred Thursday, March 25, 2010 in Brownsville, TN
Probable Cause Approval Date: 01/19/2012
Aircraft: EUROCOPTER AS-350-B3, registration: N855HW
Injuries: 3 Fatal.
NTSB investigators traveled in support of this investigation and used data obtained from various sources to prepare this aircraft accident report.
The accident pilot was preparing to return to the helicopter’s home base at night after dropping off a patient at a hospital helipad near the end of his 12-hour duty period. The oncoming pilot, who was scheduled for the next duty period, arrived at the helicopter’s home base and saw that the helicopter was gone. He was concerned about the weather and called a flight-following center, locating the helicopter on the hospital helipad. The accident pilot then called the oncoming pilot via cellular telephone and asked about the weather. He stated that he was still on the helipad waiting for the flight nurses to return and that he “wanted to get the helicopter out.” The oncoming pilot further indicated in postaccident interviews that when he suggested that the accident pilot park the helicopter on the helipad, the accident pilot said that another helicopter already occupied the lower elevation pad, which the oncoming pilot took to mean that the accident pilot did not want to leave the helicopter on the hospital’s elevated pad. The two pilots then discussed an approaching weather system. The oncoming pilot reported that the accident pilot told him that he believed he had about 18 minutes to beat the storm and return to home base, so he was going to leave the flight nurses behind and bring the helicopter back.
The oncoming pilot stated that he later called the flight nurses, only to learn that they were on board the helicopter. Rechecking visibility, the oncoming pilot then communicated with one of the nurses on board and told her that she “had the weather beat,” and she responded that they were about 30 seconds from arrival. Three witnesses near the accident site stated that they saw lightning and heard thunder at the time of the accident. One witness stated that it was very windy at the time, and another stated that heavy rain bands were passing through the area. After the oncoming pilot heard a loud clap of thunder and saw lightning, he tried to call the crew, but there was no response. The helicopter crashed in an open wheat field about 2.5 miles east of the home base.
Examination of the wreckage revealed no evidence of any preimpact failures or malfunctions of the engine, drive train, main rotor, tail rotor, or structure of the helicopter. Additionally, there was no indication of an in-flight fire.
An examination of meteorological data revealed that the helicopter likely encountered the leading edge of a line of thunderstorms, moving at 61 knots groundspeed. A portion of this line of thunderstorms included localized instrument meteorological conditions, heavy rain, lightning, and wind gusts up to 20 knots. The near-surface region immediately ahead of this advancing line, known as the “gust front,” is an area prone to extreme low-level wind shear that often occurs in clear air. Based on these conditions, the helicopter likely encountered severe turbulence from which there was no possibility of recovery, particularly at low level. No evidence existed of a lightning strike at the time of the accident.
Although the pilot encountered an area of deteriorating weather, this did not have to occur as the pilot could have chosen to stay at the hospital helipad. The pilot, however, decided to enter the area of weather, despite the availability of a safer option. Based on the pilot’s statement to the oncoming pilot about the need to “beat the storm” and his intention to leave the flight nurses behind and bring the helicopter back (even though the nurses made it back on board), he was aware of the storm and still chose to fly into it. The pilot made a risky decision to attempt to outrun the storm in night conditions, which would enable him to return the helicopter to its home base and end his shift there, rather than choosing a safer alternative of parking the helicopter in a secure area and exploring alternate transportation arrangements or waiting for the storm to pass and returning to base after sunrise when conditions improved. This decision making error played an important causal role in this accident.
At the time of the accident, the pilot was nearing the end of his 12-hour duty shift, during which he had flown previous missions and may have had limited opportunities to rest. Further, he had been on duty overnight, and the accident occurred at an early hour that can be associated with degraded alertness. The pilot’s length of time awake, his night shift, and the early hour of the accident provide risk factors for fatigue that could have significantly degraded his decision making. However, without complete evidence regarding his sleep and rest activities, the National Transportation Safety Board was unable to determine whether or to what degree fatigue contributed to the pilot’s faulty decision to attempt to outrun the storm.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The pilot’s decision to attempt the flight into approaching adverse weather, resulting in an encounter with a thunderstorm with localized instrument meteorological conditions, heavy rain, and severe turbulence that led to a loss of control. Full narrative available
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