Story ID: 004
Accidents: January 2021
By: David Jack Kenny
Caption: Preliminary and final accident reports
Word Count: 1595
Preliminary Reports
Compressor Blade Failure Detected in Submerged Helicopter

Garlick Helicopters UH-1H, Jan. 9, 2020, Ben Boyd Reservoir, New South Wales, Australia – In a second update published October 30, the ATSB reported that a borescope examination found a broken rotor blade in the compressor section of the engine of a firefighting helicopter that ditched in the Ben Boyd Reservoir following a loss of power. A subsequent teardown inspection by the manufacturer found that the number 21 roller bearing, which supports the front of the power turbine shaft, and the number 1 ball bearing, supporting the front of the rotating compressor assembly, had worn to the point that they could no longer maintain centerline alignment of their respective rotating assemblies. 

The helicopter had rolled inverted after touching down in the water, and the pilot credited his recent Helicopter Underwater Egress Training with his escape.  The wreckage was subsequently recovered for examination.

EMS Flight Crashes On Hospital Roof

Agusta A109, Nov. 6, 2020, Los Angeles – Two passengers escaped unharmed and the pilot suffered only minor injuries after a helicopter EMS flight crashed onto the rooftop helipad of the USC Keck Medical Center following an apparent loss of tail rotor authority. During a steep approach offset to the left to improve his view of the landing zone, the pilot saw no indication of wind from either the pad’s windsock or nearby trees. As he slowed the ship to 45 knots, he increased power for the approach. At about 40 feet above the pad, a slight right yaw began that he could not correct with full left pedal. It increased “violently” as he began to contemplate flying away, rendering the helicopter uncontrollable. He “dumped” the collective while trying to remain above the pad. The helicopter touched down hard and rolled onto its left side, destroying all four main rotor blades and strewing debris across the pad and onto the ground. The pilot shut down the engines, and he and the passengers were able to evacuate the wreckage without assistance.

Footage filmed from an adjacent building shows the helicopter rotating slowly clockwise about its vertical axis during the approach, then arresting its descent while rotating another 360 degrees before rotating another 180 degrees during its final descent onto the helipad. The tail rotor and 90-degree gearbox were among the components recovered from the accident site.

PC-12 Ditched on Ferry Flight

Pilatus PC-12 47E, Nov. 6, 2020, Pacific Ocean about 1,000 miles east of Hilo, Hawaii – A new, 2020-model Pilatus PC-12 NGX ditched in the Pacific on the first leg of a planned ferry flight from California to Australia following a total loss of engine power at FL 280. The two-pilot crew evacuated the aircraft through the right overwing exit and boarded their covered six-person life raft, escaping without injury. The crew of a container ship rescued them some 22 hours later.

The airplane had been fitted with an auxiliary fuel system, including a factory-installed ferry fuel fitting and check valve in the left wing, two aluminum tanks inside the cabin, transfer and tank valves, and two 30-psi transfer pumps. The flameout occurred just after the copilot transferred the last usable fuel from the rear tank. She shut off the transfer pump with fuel still visible in the transparent pressurized line, but the low fuel pressure indicator illuminated within 15 seconds, and the engine stopped and the propeller feathered before she could return to the cockpit.

The crew made multiple unsuccessful attempts to restart the engine, then committed to an ocean ditching as they descended through 8,000 feet. The pilot landed the airplane gear-up with full flaps at an angle to swells he estimated as five to 10 feet, spaced 20 feet apart. They reached Oakland Center via satellite phone and the Coast Guard initiated rescue efforts. A C-130 reached the scene about four hours later and attempted to coordinate rescue efforts by an oil tanker, but the rough seas and the speed of the ship prevented the pilots from being able to grasp the lines. A container ship using rope cannons rescued them the following afternoon.

After initially remaining afloat, the airplane is now considered lost at sea.
Final Reports
Cause of Inflight Breakup Remains Undetermined

Cessna 441, Nov. 17, 2018, Harmon, North Dakota – The NTSB was unable to identify a definitive reason why the pilot of a Conquest II air ambulance lost control of the airplane eight minutes after takeoff, causing an inflight breakup that resulted in a debris field some 2,500 feet long and 750 feet wide. A flight nurse and a paramedic also perished in the accident, which occurred at about 10:40 p.m. local time in instrument meteorological conditions. Examination of the engines and propellers found no sign of malfunction or mechanical failure, and the points at which the wing spars failed in overload showed “no evidence of any pre-existing conditions that would have degraded the strength of the airplane structure.” Weather models indicated a high probability of icing conditions, but no evidence of structural icing was found at the scene.

The flight was dispatched from Bismarck to Williston to bring a patient back to Bismarck for emergency medical treatment. The pilot filed an IFR flight plan with a cruising altitude of 14,000 feet, estimating 45 minutes en route at 281 knots. No alternate airport was filed. The 1982-model twin took off at 10:31 p.m., climbing to 14,000 feet on a direct course to Williston. Eight and a half minutes later it entered a right descending turn, losing 7,800 feet in the next 39 seconds. Radar contact was lost nine seconds later with the airplane now turning left.

The 48-year-old airline transport pilot had nearly 4,000 hours of pilot-in-command experience but only 70 in the accident make and model. The extent and currency of his experience in actual instrument conditions was not reported. The Board concluded that the failure signatures were “consistent with the pilot initiating a pull-up maneuver that exceeded the airplane spars’ structural integrity during an attempted recovery from the spiral dive” but could not pinpoint a cause for the initial deviation from his intended course.

Messages retrieved from his mobile phone contained reports of discrepancies involving the portable backup attitude heading and reference system and the panel-mounted horizontal situation indicator on earlier flights. No data could be retrieved from the enhanced ground proximity warning system or multi-hazard awareness unit.

Tail Rotor Fouled by Tether Line

Airbus Helicopters AS350, Feb. 17, 2019, Wakefield, Nelson, New Zealand – The loss of directional control necessitating a forced landing of a helicopter conducting firefighting operations was caused by the tether line suspending its monsoon bucket coming into contact with the tail rotor blades, disabling the tail rotor. TAIC investigators found that one or more of the hook-and-loop fasteners that secured the stainless-steel shape ring to the fabric bucket had detached, causing a deformation of the bucket’s shape that abruptly changed its aerodynamic stability. It then streamed out behind the helicopter until the tether rose into the tail rotor.

The pilot responded to a series of uncommanded yaws and a loud bang by jettisoning the bucket and initiating an emergency landing. When the helicopter began to spin, he made an emergency autorotation into light brush and was met within minutes by firefighters on the scene. He suffered a minor injury to one ankle. Later generations of monsoon buckets from the same manufacturer discontinued the hook-and-loop fasteners in favor of a two-piece composite ring permanently attached to the fabric.

Software Quirk Caused Engine Shutdown

Gulfstream G650, July 7, 2019, over Co. Waterford, Ireland – A discrepancy between the commanded and detected positions of the aftmost stage of the variable stator vanes (VSV) led the electronic engine controller (EEC) to shut down the Gulfstream’s left engine as it climbed through FL 290. The shutdown command was peculiar to the software governing the Rolls Royce BR700-725 series engines; in other engines in the BR700 family, a VSV discrepancy would trigger a “Do Not Dispatch” maintenance message without affecting engine operation. Teardown of the left engine found that corrosion in the bore in the compressor casing increased the torque required to activate the VSV3 vane to 129 Nm, more than 2.5 times that specified in the relevant service bulletin, and was not reduced by lubrication.

The flight departed Shannon International for Farnborough, U.K., with two pilots, one passenger, and one cabin attendant. Climbing through FL 290, an amber “L Engine Maintenance” warning on the Engine Indicating and Crew Alerting System was followed almost immediately by a red “L Engine Fail” message. Electrical load-shedding after the shutdown caused a momentary loss of air data to the right engine, which reverted to an alternate control mode and disabled the onboard satellite telephone. 

The crew leveled the ship at FL 310 and, after some discussion, chose to return to Shannon via a gradual descent profile. En route, they declared an emergency, and after discontinuing the first approach due to a gear-door warning message, landed without further incident.

Rolls-Royce had modified the BR725’s EEC software to conform to that of other BR700-series engines following a similar event in September 2018, but operators were given two years to perform the update. It had not yet been done on the subject airplane. Following this episode, the update was expedited and completed on all BR725 engines by September 2019. Rolls-Royce also issued a service bulletin mandating torque checks on all engines older than 24 months and added a scheduled maintenance task of re-lubrication every 1,200 flight hours or 48 months, whichever comes first.