Introduction
On June 10, 2010, at approximately 1034 central daylight time, a Bell 206 L-3 helicopter, registration N108PH, operated by Petroleum Helicopters Incorporated (PHI) of Lafayette, Louisiana, experienced a possible tail rotor failure while en route to an oil platform in the Gulf of Mexico. The helicopter made a forced landing on the water and subsequently rolled inverted due to partial deployment of the emergency floats. The commercial pilot was not injured, and the two passengers sustained minor injuries. A company visual flight rules flight plan was filed for the on-demand air taxi flight conducted under 14 Code of Federal Regulations Part 135. Visual meteorological conditions prevailed. The helicopter had departed PHI's base in Port O'Connor, Texas, around 1000, destined for Mustang Island Block 103.
Incident Narrative
According to the pilot, this was his third flight of the day. The flight was normal until approximately 10 minutes from the platform at an altitude of 900 feet. He reported hearing a pop, followed by the aircraft pitching down and to the right with strong vibrations. He lowered the collective and stabilized the aircraft, noting that the engine was running normally (rotor speed approximately 101 percent) but there was no response from the pedals. A brief attempt to apply collective resulted in a right rotation, indicating the helicopter was not controllable. The pilot entered a full autorotation, brought the throttle to idle, and deployed the emergency floats before the flare. He observed the floats start to inflate but noted that the center float on the right side did not inflate. After a controlled landing on the top of a swell, the helicopter settled and rolled to the right, becoming inverted almost immediately. The pilot did not activate the emergency life raft switch. He exited the helicopter once fully inverted, inflated his life vest underwater, and surfaced to see the two passengers. One passenger had not inflated his vest, and the other helped him. The three held onto the skids of the helicopter, which was about one foot under water, and waited for a rescue boat from a nearby barge. The pilot noted no damage to the underside of the tail boom and could see one tail rotor blade. He did not use the external emergency t-handle for the life rafts because the rescue boat was approaching rapidly.
Passenger Account
One passenger, seated in the front left seat, described the flight as normal except for a strong headwind. About 30 minutes into the flight, at 900–950 feet, the helicopter suddenly pitched over almost 90 degrees without warning. He described it as a sudden "nose dive." He and the pilot hit their heads on the cabin roof. The pilot regained control, leveled the helicopter, and attempted to fly forward. The pilot stated, "This ain’t gonna work…we lost our tail rotor." Almost immediately after, the pilot deployed the floats and said, "we’re gonna roll." The passenger estimated the time from the nose dive to landing was 10 seconds, describing the touchdown as normal. Within 1–2 seconds, the main rotor blades contacted the water (the engine still under power), and the helicopter rolled right and inverted. The passenger removed his headset, unbuckled his seatbelt, and exited through the left front door. Once his head was above water, the helicopter was completely inverted and floating just below the surface. He saw the other passenger, swam to him, and inflated his life vest. All three climbed onto the belly of the helicopter. The tail boom was still attached, but the condition of the tail rotor was uncertain. They saw the rescue boat from a nearby barge about 150 yards away approaching. The pilot did not discuss deploying the external life raft because the boat was so close. The boat crew used a ladder to help the pilot and the passenger aboard; divers assisted the other passenger, who was injured. A tugboat approached, and divers tied the helicopter to the tug for towing to the barge. The rescue boat was instructed not to dock at the barge because the Coast Guard needed a clear deck. The boat returned to the tug to pick up divers, by which time the seas had become rough. The passenger noted that the tail boom had separated from the helicopter, likely due to towing and wave action.
Investigation
The tail boom, aft portion of the left skid, and attached aft float were not recovered. The main body of the helicopter, including the main rotor system and engine, were recovered and examined at PHI's facility in Lafayette, Louisiana, on June 14–15, 2010, by the Investigator-in-Charge along with representatives from Apical Industries, Inc., Bell Helicopter, PHI, and Rolls Royce. Examination of the engine and airframe (minus the tail boom and tail rotor) revealed no pre-mishap anomalies.
Float System Findings
The emergency float system consisted of six floats: one attached to each skid at the forward, mid, and aft positions on each side. The floats were connected to a helium reservoir that supplied compressed gas through a system of hoses to specific fittings. Each fitting was designed to regulate gas flow to a particular float to ensure simultaneous inflation despite varied capacities and distances. Examination of the recovered floats showed that the right-side mid float had burst from excessive pressure and that the aft float did not fully inflate. Investigation revealed that the hoses from the mid and aft floats had been installed incorrectly to the port fitting; they were interchanged (crossed). This allowed unrestricted and excessive gas flow to the mid float, causing the burst. The aft float received insufficient gas.
Maintenance and Recommendations
In October 2006, Apical Industries, Inc., had released a Service Instruction Letter addressing customer concerns about proper installation of the emergency floats. The letter warned: "CAUTION…The port fitting incorporates restricted orifices to manage the flow of gas to each of the floats. Incorrect routing of hoses from the port fitting may result in low inflation pressures in some chambers of the floats and rupture of other chambers. Check to ensure that the hoses are routed according to the figures below." The letter included photographs and diagrams with part numbers. A review of maintenance records showed that the three-year test/inspection of the emergency float system was last completed by PHI maintenance personnel in March 2010, and the improper hose installation on the incident helicopter should have been identified at that time. The Safety Board issued a safety recommendation to Apical Industries to redesign the hoses to minimize the risk of maintenance personnel interchanging them during installation.