PRELIMINARY REPORTS
Reported Weather Points to Reduced Visibility in Alaska Helo Fatal
Airbus Helicopters AS350B2, near Skagway, Alaska, May 6, 2016–The commercial pilot died when his helicopter struck snow-covered terrain four miles southeast of its destination in marginal day VMC. The Part 135 on-demand charter flight originated from the operator’s heliport in Skagway at 6:40 p.m. local time and was operating under a VFR flight plan. The helicopter was returning to the heliport when the accident happened at 6:55 p.m.
According to the preliminary report, after dropping off a passenger and 12-dog sledding team at a remote camp on the Denver Glacier, the helicopter flew toward a previously used aerial return route to the southwest before turning north. A second helicopter was dispatched after the accident aircraft was classified as overdue, and crews found the wreckage near a frozen glacial lake in steep mountainous terrain two miles northeast of the dog sledding camp, resting on its left side with the tail boom separated.
Reported visibility along the aerial return route was a quarter mile, and to the north of the dog sledding camp visibility was reported as about a half mile. At 6:53 p.m. the nearest official weather observation station at Skagway Airport (PAGY) reported conditions as wind from 210 degrees at 19 knots, gusting to 28 knots; visibility 10 sm; few clouds at 8,000 feet; temperature 53 degrees F and dew point 37 degrees F; altimeter 29.81 in Hg.
Pilot Regains Control After Pressurization Failure and Loss of Consciousness
Cessna Citation I/SP, near Texarkana, Ark., May 23, 2016–A loss of cabin pressure at FL430 in the night sky led the pilot to lose consciousness, and the jet entered an uncontrolled descent. The pilot regained consciousness and control of the airplane at 7,000 feet msl and was able to land without further incident. The pilot was not injured. The flight had departed from Perryville Municipal Airport (K02) in Perryville, Mo., and was bound for San Antonio International Airport (SAT) in Texas.
Post-flight examination of the airframe revealed substantial damage to both wings from the excessive airframe loading during the descent and recovery, and inspection of the pressurization system revealed the primary pressurization duct into the cabin was detached from its connection to the water separator. The duct’s metal retaining clamp was present and intact, with its retaining screw in place, and was found resting around the metal duct leading to the separator.
FACTUAL REPORTS
Throttle Assembly Wear in Air-tour Training Accident
Airbus Helicopters EC130B4, near Grand Canyon, Ariz., June 8, 2013–NTSB investigators noted “a number of abnormalities,” including an out-of-place throttle return spring, during their examination of an air-tour helicopter that experienced an engine control malfunction and crashed during a training flight three years ago.
According to the updated factual report, the accident happened during a training flight operated by air-tour company Papillon Grand Canyon Helicopters in day VMC. The certified flight instructor (CFI) and recently hired pilot receiving instruction were not injured. The flight departed Grand Canyon National Park Airport (GCN) at 8:15 a.m. local time, with a planned destination of Valle Airport (40G).
Following several uneventful training maneuvers, the CFI initiated a simulated engine failure three miles northeast of Valle Airport. While descending through 200 feet agl the instructor attempted to arrest the descent by rolling in the throttle, but found the twist grip had seized; unable to increase power, he autorotated to a landing. The helicopter’s skids hit dirt terrain in a nose-down attitude, and during subsequent “rocking” the main rotor struck and severed the tail boom.
Disassembly of the pilot’s and copilot’s throttle controls on the collectives revealed the return coil spring grab in the pilot’s twist grip control had traveled out of its notched seat on the tube assembly, which the Board noted would make it more difficult to move the throttle twist grip between the flight and idle positions. Investigators also noted the “operator’s method of storage” had resulted in bending and tearing of the rubber shield where the engagement notch would make contact if the throttle was in the idle position.
Maintenance personnel further noted evidence of foreign object debris damage in the collective pitch torque tube block, and pinching of the wiring harness at the bottom of the copilot’s collective. Heavy wear on the pilot’s throttle twist grip further indicated “that the pilot collective was stiff or harder to manipulate than it should have been,” according to the NTSB.
Troublesome Citation Trim Tab Actuator Tied to Jammed Trim on Takeoff
Cessna Citation S/II, Tampa, Fla., Oct. 4, 2014–The aircraft had just departed Tampa International Airport (TPA) for a short flight to Gainesville, Fla., in day VMC. The copilot was flying the aircraft from the right seat. At 400 feet agl at V2 plus 10 knots, the crew retracted the flaps and turned to the right for the published departure procedure, at which time the copilot reported that the controls were stiff and pushing back against his inputs.
The captain twice advised the copilot to trim the forces away, and he saw the copilots arms were “fully extended” pushing the yoke forward to maintain a stable climb attitude. Efforts to use electric and manual pitch trim to correct the anomaly were unsuccessful, as were hitting the trim disconnect switch and pulling the trim circuit breaker, both standard procedure in the event of a trim runaway condition. The secondary pitch trim remained frozen in the takeoff position.
The crew declared an emergency, and with careful throttle and control inputs they were able to bring the speed down and turn back to the airport. After lowering the flaps to the landing position and extending the gear, the crew reported the aircraft had become more controllable in pitch, and they successfully flew a visual traffic pattern back to an uneventful landing on Runway 19L at TPA.
Post-flight examination of the airplane revealed that with no power on the airplane, and using normal hand pressure, the manual elevator pitch trim would move no more than an inch. When released, the trim popped back to the same position. Nose-down movement felt like it was binding, while nose-up trim appeared normal. The trim moved sluggishly with electrical power on and electric pitch trim activated.
Attempting to isolate the issue, investigators removed, cleaned and lubed the left screw of the left elevator trim tab actuator assembly. When this piece was reinstalled, further inspection revealed the primary and secondary sprockets were separated from the left internal screw (part number [P/N] 5565450-45). The affected left elevator trim tab actuator assembly (P/N 5565450-79, S/N 0378-80) with the fractured screw was then retained for examination by the NTSB Materials Laboratory, which found that the two-sprocket assembly shaft was jammed inside the actuator and could not be rotated manually.
The lab determined that flat roller bearings were missing from both the actuator assembly and actuator housing, and investigators found visible corrosion on the flanges and ends of both assembly shafts. The two-sprocket assembly was disassembled, and the separated end of the mating shaft was found in two pieces between the sprockets. Inspection of these items with a stereo zoom microscope showed the fractures through the shaft end of the internal screw had occurred at the holes for the stake pin, with evidence of overstress on areas that did not have mechanical damage.
The left elevator trim tab actuator assembly is an on-condition item, and had last been installed new on the aircraft on Aug. 8, 1990, at a total airframe time of 1,545.1 hours. There was no record of part removal, overhaul or replacement since that time; a Phase 2 inspection of the assembly, required every 300 hours or 24 months, was last performed on March 7, 2014, at recorded total airframe time of 7,908 hours, with 8,105 hours recorded at the time of the incident.
Since 1995, ten FAA Service Difficulty Reports have been submitted for the part number of the elevator trim tab actuator assembly. Three of those reports were associated with pitch trim, and one of those reports indicated the sprocket separated from the internal screw after separation of the pin that secures the sprocket to the internal screw. The second report indicated that water was found in the actuator housings following inoperative manual and electric pitch trim, and the third report indicated that following a jammed elevator trim, the actuator was worn and the chain on the actuator was very loose and noted to bind when nose-up trim was selected.
While the NTSB noted that none of the reports filed since 1995 mentioned a fractured internal screw, such failures were identified in two reports filed on the same part number before 1995.
FINAL REPORTS
Cause of FCU Bearing Failure Undetermined in Texas EMS Accident
Airbus Helicopters AS350B2, near Texarkana, Texas, June 23, 2014–Failure of two fuel control unit (FCU) drive bearings led to uncommanded engine acceleration and overspeed and a hard landing for an EagleMed medevac helicopter two years ago, but NTSB investigators could not determine why those bearings failed.
According to the Board’s probable cause report, the Part 135 emergency medical services flight had departed Idabel, Okla., at 1:20 p.m. local time bound for Texarkana in day VMC. The helicopter was cruising at 1,000 feet agl when the commercial pilot noticed the rotor rpm had rapidly increased, and the high rotor speed alarm sounded. The pilot attempted an autorotation to a nearby field after he was unable to reduce the rotor speed, and the helicopter was substantially damaged in the run-on collision with the ground. The main rotors partially severed the helicopter’s tail boom, and the front of the left skid was damaged. The pilot and two flight crewmembers were not injured and were able, without assistance, to extract the patient on board.
Disassembly of the FCU revealed the two drive bearings that maintain drive integrity between the FCU and the fuel pump had failed and no longer provided axial or radial positioning of the FCU drive shaft. The splined fuel pump to FCU coupler spun freely on the FCU drive shaft, leading to excessive wear that degraded the driveshaft to the point that it could no longer provide positive drive to the FCU. The FCU interpreted this condition as an underspeed condition, leading it to command more power from the engine.
Metallurgical testing of the FCU drive bearings did not reveal why they had failed. As a result of this accident, engine manufacturer Honeywell adjusted the FCU bearing replacement schedule for the LTS101-700-D from a one-time replacement interval to replacement every 600 hours.
Nonfatal Dynamic Rollover Event Led to Reevaluation of Operator’s Procedures
Airbus Helicopters AS350B2, near Key Lake Airport, Saskatchewan, Jan. 21, 2016–An unanticipated increase in cable tension during electrical transmission line stringing operations set off a chain of events that felled an AStar operated by Airspan Helicopters and seriously injured the sole-occupant pilot, according to a final report issued by the Transportation Safety Board of Canada (TSB).
Stringing operations entailed pulling feeder cable through a series of electrical transmission towers, each approximately 125 feet agl, using a 37-foot-long “needle.” The pilot had completed the first 10 towers on which the flight was working without incident, but while threading the 11th tower in day VMC the needle lunged and abruptly stopped, possibly because it contacted the tower or because the feeder cable snagged something on the ground.
Investigators determined that this abrupt rise in cable tension, combined with “a slight drift of the aircraft” in a crosswind, led to an uncommanded roll and rotation to the left. The pilot jettisoned the cable and attempted to arrest the descent, but within three to five seconds of the initial lunge, the helicopter struck the ground. There was no post-impact fire, and the pilot was able to exit the wreckage and await rescuers notified by the operator’s satellite-based search-and-rescue system.
The TSB asserts that the company’s prior training procedures did not suitably prepare pilots for abnormal flight conditions, and that other normal checks and procedures were often not followed. The report cited inadequate ground monitoring and failure to wear shoulder harnesses. Investigators could not determine if an electrical emergency cable disconnect system had been activated for the accident flight; the pilot used a mechanical disconnect to jettison the cable.
After the accident, Airspan temporarily suspended AS350 line stringing operations and reviewed and amended its standard operating procedures, particularly pre-flight checks, stringing operations and feeder cable-pulling procedures. The company also hired a third-party consultant to revise its safety management system (SMS); although an SMS is not currently required by Transport Canada for operations such as Airspan’s, the issue is high on the Board’s “Watchlist” of safety-related requests. “As this occurrence demonstrates, some transportation companies are not effectively managing their safety risks,” the TSB noted.