# NTSB FTW94FA158: Bell 47G-2, N47GY, Tulsa, OK, May 16, 1994 - Type: NTSB accident investigation - Classification: Accident · Fatal · Field investigation · Final report - Date: May 16, 1994, 15:02 local (20:02 UTC) - Place: Tulsa, OK - Coordinates: 36.020656, -95.929634 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=36.0207&lon=-95.9296&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: Fatal - Injuries: 1 fatal - Status: Completed, report December 7, 1994 - Report: Approved by Office Director - NTSB case key (mKey): 18899 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW94FA158 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18899/pdf - Page: https://openairdocs.org/ntsb/FTW94FA158 ## Probable cause IN FLIGHT LOSS OF CONTROL DUE TO THE PILOT'S IMPROPER USE OF THE CYCLIC AND COLLECTIVE CONTROLS WHEN HE MANEUVERED ABRUPTLY TO AVOID COLLIDING WITH A FLOCK OF BIRDS. FACTORS WERE THE BIRDS AND THE INFLIGHT SEPARATION OF THE LEFT SYNCHRONIZED ELEVATOR. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Abrupt maneuver, cruise - normal - object - bird(s) (contributing factor) - cyclic - improper use of, pilot in command (cause) - collective - improper use of, pilot in command (cause) - Airframe/component/system failure/malfunction, maneuvering - rotorcraft flight control,synchronized elev ctl - separation (contributing factor) - In flight collision with terrain/water, descent - uncontrolled - terrain condition - residential area ## Analysis WITNESSES HEARD A LOUD NOISE AND SAW AN OBJECT SEPARATE FROM THE SECOND OF TWO HELICOPTERS. THIS HELICOPTER THEN IMPACTED INVERTED IN THE BACK YARD OF A RESIDENCE. THE LEFT SYNCHRONIZED ELEVATOR AND END CAP WERE FOUND 240 FEET AWAY. AN INDENTATION ON THE LEADING EDGE OF ONE OF THE MAIN ROTOR BLADES MATCHED THAT OF THE END CAP. THE PILOT OF THE FIRST HELICOPTER SAID HE HAD WARNED THE SECOND PILOT OF A FLOCK OF BIRDS, AND THAT HE HAD TO BANK SHARPLY TO AVOID HITTING THEM. WHEN HE RECEIVED NO REPLY, HE TURNED AROUND BUT THE OTHER HELICOPTER WAS NOT IN SIGHT. ## Factual narrative HISTORY OF FLIGHT On May 16, 1994, at 1502 central daylight time, N47GY, a Bell 47G-2, was destroyed when it impacted terrain during an uncontrolled descent in Tulsa, Oklahoma. The commercial pilot was fatally injured. Visual meteorological conditions prevailed for the ferry flight. Eye witnesses were interviewed and thirteen witness' statements were submitted. The consensus of these statements revealed: The accident helicopter was following a lead helicopter [both helicopters were enroute to Tulsa Helicopters, Inc., a helicopter repair facility, for maintenance to be performed on the accident helicopter (see attached map)]. Five witnesses reported hearing a loud "pop," "exploding," or "backfire" noise. Two witnesses indicated that there was a power loss. Eight witnesses saw something separate from the helicopter. One witness saw the helicopter tilt left and go sideways. "I could see top of rotors from my view point which told me copter was completely sideways," he wrote. Another witness verbally reported seeing the helicopter roll 90 degrees to the left, and said he also saw the top of the rotor disc. Five witnesses said the helicopter went inverted, four witnesses said the helicopter entered a spin or spiral, and another witness said it "tumbled." WRECKAGE AND IMPACT INFORMATION The helicopter impacted the back yard of a residence at 3324 E. 83rd Place, causing minor damage to the chimney structure. Two of the three longitudinal tail boom trusses were found severed. Approximately 240 feet away, on the west side of Harvard Avenue, the left synchronized elevator and end cap were located. These were the only parts that were found to have separated from the helicopter. One of the main rotor blades had an indentation on its leading edge near the blade tip. Measurements made on this indentation matched those made to the elevator end cap. MEDICAL AND PATHOLOGICAL INFORMATION An examination of the body was performed by the Oklahoma State Medical Examiner's Office in Oklahoma City, Oklahoma. Toxicological examination by the FAA's Civil Aeromedical Institute (CAMI) disclosed 32.000 (ug/ml, ug/g) salicylate in the urine. According to a CAMI spokesman, salicylate is the same as aspirin. TESTS AND RESEARCH A metallurgical examination of the fractured surfaces concluded that they were the result of overload forces. Measurements taken from a three dimensional scale drawing of the Bell 47G-2 indicate that in order for the main rotor blade to contact the synchronized elevator, the rotor system would have to tilt aft approximately 18 degrees. According to a report by Bell Helicopter's Rotor System Design Group, static stops limit the angular movement of the rotor mast. In a static state, the rotor blades will clear the tailboom about 14 inches. The report noted, "In trimmed, high speed forward flight, the rotor would have about 8 degrees of collective pitch, and 8 degrees of cyclic pitch, and the rotor flapping would be near 0 degrees. However, an unusual and violent maneuver such as a maximum rate drop of the collective pitch with full aft cyclic pitch applied simultaneously could command aft flapping exceeding the stop-to-stop clearance. Under this circumstance, heavy flapping stop contact could occur, and with large mast and blade bending deflections a blade strike on the tail boom is possible." ADDITIONAL INFORMATION The lead helicopter pilot said that shortly after departing the airport, he was forced to bank sharply to avoid a flock of birds. He radioed this information to the second helicopter pilot but received no reply. When he turned around, the second helicopter was not in sight. A "Release of Aircraft Wreckage," NTSB Form 6120.15, was executed on August 3, 1994, but it was never returned by the owner. ## Aircraft - Registration: [N47GY](https://openairdocs.org/deregistered/N47GY-2011-01-03), registration cancelled 2011-01-03, S/N 2207, built 1958 (OpenAirDocs) - Reported make and model: BELL 47G-2 - Registry model: [Bell 47G-2](https://openairdocs.org/model/bell-47g-2) (registry code 1181008) (OpenAirDocs) - Registry engine: [Lycoming VO-435 series](https://openairdocs.org/engine/lycoming-vo-435-series) (registry code 41525, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 2207 - Airframe hours: 7844 - Engines: LYCOMING VO-435-A1D 260 horsepower reciprocating - Damage: Destroyed - Flight: Ferry, Part 91 - Registered owner: Cypert, Gerald - Airworthiness certificate: Standard, Normal - Departed: RVS, JENKS, OK ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 64; private, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 2, valid medical--w/ waivers/lim; seat: left; toxicology performed; flight hours: 3,919 total, 24 in this make and model, 3,283 as pilot in command, 58 in the last 90 days, 18 in the last 30 days, 2 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 120° at 5 knots - Visibility: 15 statute miles - Lowest ceiling: none - Temperature: 84 °F, dew point 61 °F - Altimeter: 30.00 inHg - Observed at: RVS, 2 nm away ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19940516011039A](https://openairdocs.org/incident/19940516011039A), May 16, 1994: Bell 47G2, Tulsa, OK, Destroyed, 1 fatal. Main rotors struck tail boom in flight. Spun out of control. Indicates abrupt control use. Large birds in area. From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.