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Mon, Jan 24, 2005

Was DC Medical Helo Downed By Wake Turbulence?

NTSB Says Passenger Jet Passed Over Less Than Two Minutes Before Fatal Accident

From the NTSB:

On January 10, 2005, at 2311 eastern standard time, N136LN, a Eurocopter EC135 P2, operated by Air Methods Corporation, d.b.a. LifeNet, was destroyed during an impact with the Potomac River near Oxon Hill, Maryland. The certificated commercial pilot and flight medic were fatally injured, and the flight nurse received serious injuries. Visual meteorological conditions prevailed, and a company flight plan had been filed for the flight. The flight originated at Washington Hospital Center (DC08), Washington, D.C., at 2304, and was destined for the Stafford Regional Airport (RMN), Stafford, Virginia. The air ambulance positioning flight was conducted under 14 CFR Part 91.

The operator of the helicopter reported that the helicopter crew picked up a patient at the Frederick Hospital, Fredrick, Maryland, and transported the patient to Washington Hospital Center, arriving at 2219.

According to flight-following Global Positioning System (GPS) data recorded by the operator, the helicopter lifted from Washington Hospital Center at 2304, and proceeded southeast and then southwest, along a route consistent with Route 1, on a National Oceanic and Atmospheric Administration (NOAA), Washington, D.C. Helicopter Route Chart. The helicopter turned to a southerly heading in the vicinity of Washington National Airport, and continued along a route consistent with Route 4, on the Washington, D.C. Helicopter Route Chart, towards the Woodrow Wilson Bridge.

A review of the NOAA Chart revealed that it depicted a maximum altitude restriction of 200 feet north of the Woodrow Wilson Bridge, and a maximum altitude restriction of 300 feet, south of the Woodrow Wilson Bridge.

Preliminary radar data provided by the Federal Aviation Administration (FAA) revealed the helicopter flew southbound (180-degree flightpath) along the Potomac River, at an altitude of 200 feet. At 2311, the helicopter was observed just south of the Woodrow Wilson Bridge, maintaining its southbound heading and 200-foot altitude. Four seconds later, the helicopter was observed on an approximate 190-degree heading, and an altitude of 100 feet. The next and last recorded radar hit, was 5 seconds later, on an approximate 200-degree heading, at an altitude of zero feet.

A Safety Board investigator interviewed the flight nurse in the hospital. According to the flight nurse, he was seated in the left front (copilot) seat, the pilot was in the right front (pilot) seat, and the flight medic was seated immediately behind the flight nurse, in the left-side, aft-facing seat.

As the helicopter approached the Woodrow Wilson Bridge from the north, it passed abeam Washington National Airport at a "lower than normal altitude," but climbed 200 to 300 feet before reaching the Wilson Bridge. About 1 mile prior to the bridge, the helicopter appeared to be at the same, or higher altitude, than the marking lights on the cranes, which were positioned near the bridge. The flight nurse "called the lights," on both sides of the river, and the pilot acknowledged him.

As the helicopter climbed, the flight nurse noticed an airplane descending towards Washington National Airport, and wondered if there would be a conflict, or a wake turbulence hazard. Additionally, he stated he was not sure what the relationship was between the helicopter and the airplane, as the airplane passed overhead.

The flight continued along the river close to the Maryland shoreline; however, as the helicopter approached the bridge, the pilot maneuvered the helicopter to cross over the mid-span of the inner loop (westbound) bridge.

The flight nurse remembered being over the outer loop (eastbound) span of the bridge, and then being submerged in the water with his seatbelt on, and his helmet off. He stated, "I don't remember striking something, but my initial reaction was that we must have hit something."

The flight nurse also stated that at no time did the Master Caution lights, or the panel segment lights illuminate. He also did not hear any audio alarms sound. The helicopter was neither high nor low, but "on altitude," relative to other flights which he had been on in the past.

The pilot did not perform any evasive maneuvers, and did not communicate any difficulties either verbally or nonverbally in the vicinity of the bridge. The flight nurse did recall observing a large white bird fly up from the lower left towards the helicopter, but made no mention of striking it. When asked what he thought might have caused the accident to occur, the flight nurse stated, "We must have hit an unlit crane."

The helicopter came to rest in the Potomac River about 0.5 miles south of the Woodrow Wilson Bridge.

The pilot held a commercial pilot certificate with ratings for airplane single and multiengine land, rotorcraft-helicopter, and instrument helicopter. His most recent second-class FAA medical certificate was issued on May 28, 2004.

According to records maintained by the operator, the pilot was hired in June 2004, at which time he reported 2,750 hours of total flight experience, 2,450 of which were in helicopters.

Examination of maintenance records revealed that the helicopter was being maintained in accordance with an FAA Approved Aircraft Inspection Program (AAIP). The last AAIP 50-hour inspection was performed on the helicopter on December 17, 2004. The last 100-hour inspection was performed on November 23, 2004, at an aircraft time of 94.5 total flight hours. The maintenance log indicated that the radar altimeter was inoperative and included a listing of the malfunction in the Approved Minimum Equipment List (MEL) record. As of January 10, 2005, the helicopter had accumulated 166.6 total flight hours.

Weather reported at Washington National Airport, at 2251, included calm winds, 10 miles visibility, broken clouds at 13,000 feet, broken clouds at 20,000 feet, temperature 45 degrees Fahrenheit, dew point 35 degrees Fahrenheit, and altimeter setting 30.25 inches of Hg.

The helicopter was recovered from approximately 5 feet of water in the Potomac River. Debris from the helicopter was recovered along a wreckage path oriented on a southbound heading, consistent with the helicopter's flight path prior to the Wilson Bridge.

The main fuselage section was separated into the lower cockpit area and upper cockpit area. The lower cockpit area contained the flightcrew floorboard section, anti-torque pedals, forward skid frame, and fragments of the ruptured fuel tank. The upper cockpit area contained the flight control tubes, the center electrical and flight control structure (broom closet), the upper flight control deck, the main rotor gearbox, rotor head, and engines.

The mechanical flight control system was assisted by hydraulic actuators and an automatic flight control system (AFCS). The system was controlled by two dual controllable pilot cyclics and collectives. For the EMS mission, the co-pilot controls had been removed. The anti-torque pedals were routed to the tail rotor servo via a Teleflex cable. The cyclic and collective controls were routed through mechanical linkages to an upper deck dual hydraulic servo control system, which controlled lateral, longitudinal, and collective control.

The cyclic, collective, and yaw controls were examined for evidence of malfunctions or pre-impact failures. Continuity could not be established due to breaks in the system and missing portions of the push-pull tubes; however, the breaks were matched and examined for evidence of pre-impact malfunction or failure. Examination of the breaks revealed no pre-impact mechanical malfunctions, and the fractures were consistent with overload fractures and water impact.

The main rotor mast was in place and intact in the main transmission. All four main rotor blades remained attached to their respective mounting areas, which bolted directly to the mast. Three out of four of the pitch change links were integral to their two attach points, the fourth (red) pitch change link was fractured in the middle. The fracture was consistent with compression bending overload.

The root ends of all four main rotor blades remained attached to the main rotor hub. Portions of all four main rotor blade tips were accounted for, and matched to their respective blades. All four main rotor blades contained overload fractures between 6-12 inches from the blade hub, and chordwise scoring on the lower blade skin in the same area. The main rotor blades contained fractures along the span of the blade, consistent with impact damage. No indications of an object or bird strike were noted along the blades.

The main gearbox remained attached to the center section of the upper airframe structure. All four mounting points were intact. The main transmission turned freely, no chips were found on the detectors, and the transmission appeared intact and functional.

Both engines remained attached to the upper fuselage section. Both engines sustained relatively minor damage, and their N1 and N2 sections rotated freely.

The main fuselage was separated from the tail boom section at the aft fuselage frame. The tail section included the tail gearbox, the tail rotor assembly and the complete fenestron assembly.

The tail rotor driveshaft was shifted about 1.5 inches forward. The aft portion of the driveshaft (carbon composite) was found fractured and torsionally cracked and deformed. The tail rotor blades remained complete and attached to the fenestron structure. A rotational scrape was noted on the fenestron shroud structure at the 5 o'clock position corresponding with the blade width.

Several of the helicopter components were retained for further examination.

Safety Board investigators examined sites along the Potomac River that matched the coordinates recorded by ATC radar data and the operator's flight-following GPS. The projected track along these locations toward the accident site was about 300 feet from the nearest crane, and no additional obstructions were observed along the track.

Five of the closest cranes along the Potomac River, near the Wilson Bridge construction project (Maryland side) were examined, and no structural damage or aircraft strike indications were observed.

A Maryland Department of Transportation traffic surveillance video was secured and sent to the Safety Board's Video Laboratory for examination. Preliminary examination revealed an aircraft flying, and then descending, over the bridge about the time of the accident. According to the video, the aircraft passed above and beyond the cranes prior to beginning its descent.

Examination of additional ATC radar data revealed that a 70-passenger Canadair Regional Jet 700 (CRJ-7), passed over the Woodrow Wilson Bridge about 1 minute and 45 seconds before the accident helicopter passed over the bridge. The radar data indicated that the helicopter passed 900 feet directly beneath the flight path of the CRJ-7, while heading in the opposite direction.

FMI: www.ntsb.gov

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