CINCINNATI, OH, USA
N911NC
Eurocopter BK-117-A4
The pilot stated he approached the lighted rooftop helipad from the southwest, at night, with light winds. The helipad and hangar were just ahead of him, and he initiated a right pedal turn to align the helicopter towards the south. He heard a loud bang, and the helicopter rotated uncontrollably, nose right. He lowered the collective, and the helicopter struck the landing area. Examination revealed the tail rotor blade ends were fragmented, and marks on the top corner of the hangar were similar to a tail rotor blade strike. Due to other helicopters parked on the ramp, the only approach was from the southwest. Winds were estimated to be from 220 degrees at 10 knots with gusts to 15 knots. Examination of the hydraulic pump and hydraulic tail rotor actuator found no evidence of failure or malfunction. Personnel reported the windsock would occasionally get caught on its support structure, and not indicate the true nature of the wind. There was no other wind information available to the pilot.
HISTORY OF FLIGHT On May 6, 2000, at 2335 Eastern Daylight Time, a Eurcopter BK-117-A4, N911NC, operated by Petroleum Helicopters, Inc. (PHI), was substantially damaged while landing at the rooftop heliport at University Hospital (8OH9), Cincinnati, Ohio. The certificated airline transport pilot received serious injuries. Visual meteorological conditions prevailed for the medivac positioning flight that originated from Lunken Airport (LUK), Cincinnati, Ohio. The flight was operating on a company visual flight rules (VFR) flight plan under 14 CFR Part 91. The pilot was completing his sixth flight of the night. He had earlier made two landings at a nearby hospital, and had left the medical flight crew there after the second landing. He then flew to LUK to refuel, and was returning the helicopter to 8OH9 when the accident occurred. The pilot reported there were two other helicopters already on the heliport when he initiated his approach from the southwest. He observed the windsock hanging limp, not changing direction, and indicating a light wind from the southwest. He planned to make a nose-right pedal turn over the touchdown area, and point the helicopter to the south upon touchdown. The pilot further reported that the helicopter crossed the edge of the landing area and was almost to a hover when he heard a "loud noise or bang" from the rear of the helicopter. Simultaneously with the noise, the left rudder pedal pushed rearward, and the nose started to move to the right. The pilot reported that he recognized this as a loss of tail rotor thrust and immediately closed the throttles/power levers. He could see the concrete surface of the landing area through the windshield and knew he was going to hit the landing area. In the Pilot/Operator Report it stated, "While on final approach on an approximate heading of 070 [degrees], and just as the pilot was initiating a right pedal turn to align the aircraft towards the South, he reported hearing a loud bang followed by a hard pedal push." The helicopter struck the ground, and came to rest with the engines still running. The pilot then shut down both engines and closed the firewall shutoffs for the fuel lines. The main rotor was still turning, and he applied the rotor brake to stop it. The pilot was then assisted out of the helicopter, and taken to the emergency room for treatment. A witness in the emergency room who was flight following the helicopter, reported that she observed its approach on a closed circuit monitor. She saw the glow of the helicopter's landing lights, then looked away for a few seconds. When she looked at the monitor again, the helicopter was at the top of the monitor screen, and rotating nose-right, faster than normal. While rotating, it was also oscillating along its longitudinal axis. She saw the helicopter fall to the landing area and come to rest. The pilot door opened and she could see the pilot inside the cockpit. She tried to call him on the radio, but did not receive an answer. An off duty pilot was in the pilot lounge, one level above the landing area. He felt the building shake, and went outside to see what had happened. He could hear the helicopter's engines running, and looked around the corner of the hangar. He saw the pilot slumped over in his seat with the main rotor turning. After a few seconds, the pilot looked up, shut down the engines, and then applied the rotor brake to stop the main rotor. Additional people then came to the rooftop heliport, and they assisted in the removal of the pilot from the helicopter. The accident occurred during the hours of darkness, at 39 degrees, 8 minutes, 14 seconds north latitude, and 84 degrees, 30 minutes, 9 seconds west longitude. OTHER DAMAGE The southwest corner of the hangar roof was damaged. PERSONNEL INFORMATION The pilot held an airline transport pilot certificate for rotorcraft - helicopters, with a VFR type rating in the Bell 47. In addition, he held a commercial pilot certificate for rotorcraft - helicopter, and instrument helicopter. He was last issued a Federal Aviation Administration (FAA), second class airman medical certificate, on March 20, 2000 with a limitation to wear corrective lenses. The pilot had been employed by PHI for several years, operating in the Gulf of Mexico, and performing daytime rooftop landings on offshore oil platforms. He requested and was reassigned to Cincinnati, his first emergency medical services (EMS) assignment. According to company records, the pilot had received his initial BK-117 training from PHI, and passed his checkride on August 2, 1999. He passed another checkride on December 20, 1999. No problems were noted on his training form or checkrides. According to PHI, the pilot's total flight experience was 10,379 hours, with 189 hours of night flight experience. His total flight experience in the BK-117 was 91 hours. In the preceding 90 days, he had flown 30 hours, which included 8.5 hours of night flight experience, and 44 night landings. AIRCRAFT INFORMATION The helicopter was configured for medical work. The flight controls for the left front seat had been removed. In addition, there was a side-facing bench seat, and space for a stretcher. The pilot reported that, at the time of the accident, the fuel load was about 985 pounds. METEOROLOGICAL INFORMATION Following is a list of the winds from surrounding airports with their distance and bearing from 8OH9. Airport Time Distance Bearing Winds LUK 2353 4.4 NM 121 Calm CVG 2351 9.2 NM 238 Calm The closest weather-reporting site to the accident site was LUK. At 2253, and again at 2353, LUK reported visibility's of 1/4 mile and fog. The off duty pilot who assisted the accident pilot out of the helicopter reported the weather conditions on the landing pad right after the accident as, "...[visibility] better than 5 miles, winds variable at 5 to 10 kts, with slightly higher gusts." An archived, base radial velocity image from the NEXRAD radar at Cincinnati, Ohio (elevation 1,171 feet), revealed a wind from the southwest at 20 knots or greater within about 1,500 feet of the surface, at the time of the accident. The terrain between CVG and 8OH9 was rolling. CVG had an elevation of 897 feet. The terrain increased to 914 feet just prior to the Ohio river, and then dropped to 460 feet at the river. After crossing the river, the elevation climbed to 886 feet, and stayed near that for the next three miles, where it dropped to 490 feet, and then climbed to near 800 feet. The heliport was mounted on the roof of one of the buildings. AIRDROME INFORMATION (Destination) The heliport had a lighted concrete surface, which measured 114.5 feet wide and 75 feet deep. The landing perimeter was outlined by red obstruction lights, and lights on the roof of the hangar illuminated the landing area. According to FAA data, the published elevation of the site was 915 feet. The investigation found that the correct elevation was 937 feet. A hangar and building occupied the north side of the landing area. There were three designated landing pads. Pad 1 was on the east-side, pad 2 was on the south side, and pad 3 was on the west side. An illuminated windsock was located on the roof of the hangar, about 40 feet above the landing area. The lead mechanic and lead pilot for PHI at the University Hospital base both reported the windsock would periodically catch on its structure, and at other times was free. There were no photographs taken of the windsock on the night of the accident, and none of the people who initially responded to the scene remembered checking it. Examination of photographs taken by PHI on June 7th revealed that the windsock was free. The windsock was snagged when viewed on May 8, 2000, during the day. The accident investigation team returned to visit the landing area on the night of May 8, 2000, with the off duty pilot. At the time of the visit, the team estimated the winds as predominately from the southwest at 10 knots with higher gusts to 15 knots. However, there were periods of calm winds, and other times the winds swirled around the buildings in different directions. The off duty pilot stated that the winds were similar to those he observed when he walked out on the heliport immediately after the accident. On May 9, 2000, the accident investigation team climbed to the roof and examined the windsock. The winds were similar to those observed the preceding night. The windsock appeared to be limp, indicating a light wind from the southwest. Examination of the windsock revealed, that the end of the windsock was caught on a horizontal pipe midway up it's support. When the windsock was freed, it stood nearly straight out, indicating a wind from the southwest, and moved back and forth in a plus or minus 15 to 20 degree arc. WRECKAGE AND IMPACT INFORMATION The helicopter was examined at the accident site on May 8th and 9th. Prior to the arrival of the Safety Board, the helicopter had been rotated on the pad and the main rotor blades, which were not damaged, were removed to allow more room for arriving and departing medivac helicopters. In addition, the tail rotor gearbox, which was attached to the tailboom by the pitch change rod, was removed to prevent further damage. Loose debris had also been gathered up so it would not blow off the roof or make contact with the rotor systems of the operating helicopters. The skids of the helicopter were spread and the fuselage touched the ground. There was a small fuel leak under the fuselage. There were wrinkles on both sides of the fuselage from top to bottom. Flight control continuity was verified between the rudder pedals, collective and cyclic, and their respective pitch change control rods. The 90 degree gear box and top 6 inches of the vertical fin had separated from the lower portion of the vertical fin. Compression wrinkles were found on the right side of the fracture. Both halves of the fractured tail rotor structure were forwarded to the Safety Board Material Laboratory. Metallurgical examination revealed the fracture surfaces were consistent with over load. Fuel was found in the lines leading to the engines. The fuel filters contained fuel and were absent of debris. Both engine compressors rotated freely. There was no evidence of damage to either the inlet compressors or exhaust turbines. The main rotor head rotated without binding and the freewheeling clutch was operational. The cockpit had been secured, and there was no documentation that contributed to the investigation. Two vertical cuts were found on the southwest corner of the hangar roof. The cuts were through the dark red painted metal edge of the roof. One cut measured 6 inches deep and the other measured 3 1/2 inches deep. The cuts were separated by 1 3/4 inches. A scrape mark was found on the edge of the hangar wall. The tail rotor blades, which were originally 30.15 inches in length, were reduced to a length of about 21 inches each. Small pieces of blades, blade skin, and interior foam were recovered from the landing area. A 9-inch long piece of leading edge tail rotor blade was recovered. The leading edge had impact damage, chord wise scratches, and a dark red paint transfer on it. The dark red paint transfer marks on the blade visually matched the dark red paint on the metal edge of the roof. MEDICAL AND PATHOLOGICAL INFORMATION Toxicological samples had been taken from the pilot. However, when the pilot was not admitted, the hospital elected to discard the samples were prior to the arrival of the Safety Board investigator. TESTS AND RESEARCH The helicopter was equipped with two hydraulic pumps, which were powered by the main rotor transmission. The number two hydraulic pump powered the tail rotor pitch control actuator. Both the pump and actuator were examined under the supervision of FAA inspectors. According to the FAA inspectors, no problems were reported for either unit. ADDITIONAL INFORMATION The center of pad 2 was located 51.5 feet south of the hangar and 22 feet from the western edge of the landing area. The BK-117 main rotor diameter was 36 feet, and the aft tip of the tail rotor was located 30.3 feet aft of the main rotor mast. The cockpit was located 5.6 feet forward of the main rotor mast. With the main rotor mast located over the center of the desired landing area, the aft edge of the tail rotor was located 21.2 feet from the hangar. The height of the hangar roof was 22 feet above the landing pad. The height of the tail rotor drive shaft was 11 feet above the ground, as measured from sitting on the ground. On the night of the accident, another BK-117, on call for medivac duty, occupied pad 1. A Eurocopter BO-105 helicopter, main rotor diameter 32.2 feet, occupied pad 3. This helicopter was an unassigned spare, used as a backup helicopter if either of the two primary helicopters became unavailable. PHI personnel reported that the spare helicopter was normally kept in the hangar, but had been left out on the night of the accident. The investigation revealed that when pad 1 and pad 3 were occupied, the only approach to pad 2 was from the southwest. Adjacent to the west-side of pad 2 was a U-shaped open area, about 50 feet wide, which extended to street level. The open side of the U was pointed south, and was about 50 feet wide. The accident pilot and other pilots reported that when landing at pad 2, the final part of the approach was partially over the U-shaped open area. The aircraft wreckage was released to the chief pilot of Petroleum Helicopters on May 9, 2000.
the pilot's misjudgment of his closure rate, while turning to land on the rooftop helipad, which resulted in a collision with the building. Factors in the accident were the tailwind and the stuck windsock.
Source: NTSB Aviation Accident Database
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