AS50, manoeuvring, East River New York USA, 2018
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|On 11 March 2018, an Airbus AS350 engine failed during a commercial sightseeing flight and autorotation was initiated. The pilot then noticed that the floor-mounted fuel cut-off had been operated by part of the tether system of one of the five passengers but there was insufficient time to restore power. On water contact, the automatic floatation system operated asymmetrically and the helicopter submerged before the occupants could evacuate. Only the pilot was able to release his harness and escape because the unapproved adapted passenger harnesses had no quick release mechanism. The Investigation found systemic inadequacy of the operator’s safety management system.|
|Actual or Potential
|Airworthiness, Loss of Control|
|Aircraft||AEROSPATIALE AS-350 Ecureuil|
|Type of Flight||Public Transport (Passenger)|
|Take off Commenced||Yes|
|Tag(s)||Inadequate Airworthiness Procedures,|
Inadequate Aircraft Operator Procedures,
Ineffective Regulatory Oversight,
|Tag(s)||Loss of Engine Power|
Evacuation difficulties in Water
|System(s)||Equipment / Furnishings|
|Damage or injury||Yes|
|Fatalities||Most or all occupants (5)|
|Causal Factor Group(s)|
On 11 March 2018, an Airbus Helicopters AS350 B2 (N350LH) being operated by Liberty Helicopters on a commercial sightseeing flight around Manhattan in day VMC and carrying five passengers made an autorotation to controlled ditching in the East River after the engine stopped but the automatic flotation system failed to inflate symmetrically and the helicopter immediately rolled over before the occupants could exit and only the pilot was subsequently able to escape. The helicopter remained underwater supported by its partially inflated flotation system until recovered and moved to a hangar the following day.
An Investigation was carried out by the NTSB. The installed image and data recorder, which should have captured imagery of the cockpit instrument and caution/warning panel, pilot inputs to the flight controls and the near-distance external environment, and which should have detected and recorded the helicopter’s position, altitude, roll, pitch, yaw, heading and the angular velocity and acceleration in all the three axes, was found to be inoperative. Its most recent recorded data were over three years old and it had evidently been inoperative since then despite an annual functional check being required in the AMM. However, useful information was available from a digital camera mounted on the ceiling of the helicopter’s passenger cabin and a smartphone belonging to one of the passengers. Smartphone videos of the accident provided by ground witnesses were used to estimate the helicopter’s touchdown point, ground track, ground speed and rate of descent rate.
It was noted that seats on the accident flight had been sold by a separate company ‘Fly NYON’ as seats on an “aerial photography flight” during which passengers would be able to take photographs while extending their feet outside of the helicopter’s removed or open doorways when permitted to do so by the pilot. This was achieved by conducting the flights with the two right side doors and the front left door removed altogether and the left sliding door locked in the open position. Passengers in the rear left and right outer and front left seats could swivel their seats 90° and the left and right inner rear seated passengers were able to leave their seats and sit on the floor at the open doors (see the illustration below).
To ensure that passengers could not fall out, each passenger was fitted with a NYONair-provided body harness/tether system attached to an anchor point in the cabin. This ‘Passenger Safety Restraint System (PSRS) was additional to and quite separate from the mandatory FAA approved lap belt and shoulder harness system. Only the latter was worn by the pilot. Each passenger also wore a headset that enabled them to hear instructions given by the pilot.
It was noted that Liberty Helicopters, an established Part 135 and Part 91 operator which was approved to operate ‘conventional’ air tours with ‘doors-on’ helicopters had been contracted to operate flights for FlyNYON since late in 2017 and the latter had supplied the harness/tether system which Liberty Helicopters had installed. However, unlike Liberty’s own doors-on tour flights, the flights for FlyNYON were explicitly operated under Part 91 as “aerial photography flights” using a longstanding exemption which allowed such flights to be operated outside the scope of the significantly greater regulatory and oversight requirements applicable to Part 135 operators as well as having the effect of excluding regulatory oversight of significant aspects of a Part 91 operation - such as the SPRS - despite the operation being clearly a “commercial revenue-passenger carrying” business.
The 33 year-old pilot involved had a total of about 3,100 flying hours experience, of which 1,430 was on type. The 30 minute ‘sunset’ accident flight was his fifth of the day during a duty period which had begun at 0930. He had been employed by Liberty Helicopters as an A350 pilot for almost two years at the time of the accident.
The flight departed from the Helo Kearny Heliport (65NJ) in New Jersey just before sunset. After initially turning south and flying in the vicinity of the Statue of Liberty with the two inboard rear passengers having removed (with the pilots permission) their mandatory harness and moved to sit on the floor held by their PSRS, the helicopter had proceeded not above 2000 feet QNH as cleared up the East River (see the ground track illustrated below). During this time, video evidence showed that the front seat passenger had manoeuvred himself to take photographs in such a way that the loose tail of the PSRS tether attached to the back of his harness had hung down loosely near the helicopter’s floor-mounted controls. Then after returning to a more upright seated position, “his tether tail appeared taut and was extended in the direction of the floor-mounted controls”. A few seconds later, he could be seen to have “pulled on the hand grip (mounted on the helicopter’s left door frame) to adjust his seating position” and as he did so, his tether tail remained taut but appeared to “pop upward”. A couple of seconds later, as the helicopter turned towards Central Park, audio from the onboard video recorded a sudden reduction in engine noise.
The pilot responded to the apparent loss of power by initiating an autorotative descent from a height of 1900 feet and, after judging that Central Park was too crowded, had commenced a right turn back towards the East River. During the descent he checked the Fuel Flow Control Lever (FFCL), one of three floor-mounted controls (see the left hand illustration below) and confirmed that it was “secure in its detent”.
Subsequently, he stated that when the helicopter was about 600 ft above the river and he was “committed to impact”, he had reached down to position the Fuel Shut Off Lever (FSOL), another floor-mounted control, to the closed position but found that it was already closed as a result of the front seat passenger’s tether tail having snagged the lever (as illustrated in the right hand illustration above) and pulled it up. He had immediately opened it and engaged the engine starter but by this time, there was insufficient time left to achieve a restart and he declared a ‘MAYDAY’ to La Guardia TWR and activated the emergency float system using the lever on the cyclic control (see the illustration below). With the helicopter about 100 feet above the water, the onboard video recorded a single ‘click’ sound followed by the noise of float deployment. The pilot stated that he had taken this ‘pop’ sound to indicate that the flotation system - three air bags at each skid - had deployed and had seen the front of both the left and right floats and had detected the extra drag their deployment had created.
Shore witnesses’ videos showed the helicopter touching down upright and in a slightly shallow flare attitude before immediately beginning to roll to the right with the rotor blades striking the water within about five seconds of touchdown and the roll continuing so that the helicopter was “completely inverted and submerged with only the floats visible” only 11 seconds after touchdown. The pilot reported that he had been fully underwater and unable to release the buckle on his own installed, FAA-approved restraint to escape. None of the five passengers surfaced and divers subsequently found that none of them had been able to release themselves from their SPRS harness/tether systems, an action which would have required them to use a cutting device in a pouch attached to their harnesses to sever the tether.
Following the accident, the wreckage was moved, still inverted, to a pier where it could be seen that three of the six floats were under-inflated and that two of these were on the right hand side (see the illustration below), which would have created the asymmetry which led to the roll on touchdown. It was noted that the AS350 B2 helicopter is not certified for ditching but the accident helicopter, which the operator used in both Part 135 and Part 91 flight operations, had been equipped with a Dart Aerospace STC-approved emergency flotation system which was designed so that the pilot could “pull the handle to fully deploy the floats using only the right hand (the hand operating the cyclic control) without letting go of the cyclic grip (similar to how a bicycle brake lever is operated without letting go of the handlebar)”. However, no description or illustration of the system or of the intended single-handed activation technique could be found and there was no specification of the lever force required to fully activate the system.
The pilot stated that he had believed that the system was fully activated after the ‘pop’ he had heard but examination of the system found it to be have been fully serviceable when deployed but with only one of the two installed compressed nitrogen gas reservoirs having discharged its contents into the floats. Testing was able to demonstrate that the activation lever had not reached its full travel when the first ‘pop’ had occurred and that a second such ‘pop’ was likely to have occurred when the other gas reservoir discharged. It was concluded that the sequential rather than simultaneous operation of the two reservoir discharge valves in this case was a consequence of a slightly mis-positioned activation cable junction box where the activation cable was attached to the two individual reservoir valve release cables.
The Findings from the Investigation as formally documented included, but were not limited to, the following:
- The helicopter’s landing was survivable; however, the NYONair-provided harness/tether system contributed to the passenger fatalities because it did not allow the passengers to quickly escape from the helicopter.
- The Federal Aviation Administration’s (FAA) approval process for supplemental passenger restraint systems (SPRS) that was implemented after the accident is inadequate because it does not provide guidance to inspectors to evaluate any aircraft specific installations or the potential for entanglement that passengers may encounter during emergency egress.
- Although the crossover hose in the accident helicopter’s emergency flotation system design did not perform its intended function to alleviate asymmetric inflation of the floats during a single-reservoir discharge event, buoyancy stability testing showed that even symmetric distribution of the gas from only one reservoir would not enable the helicopter to remain upright in water.
- Although the accident pilot was aware that each gas reservoir may not discharge simultaneously, the high forces required to pull the activation handle, along with the aural and visual cues following a single-reservoir discharge, led the pilot to mistakenly believe that he had successfully pulled the handle fully aft to fully inflate the floats.
- Improved guidance for aircraft certification offices for assessing design features, usability, and inspection methods that ensure successful deployment of an emergency flotation system could help ensure that these important aspects are considered during the certification review process for such systems.
- Through their repeated lack of involvement in key decisions related to Liberty Helicopters operated FlyNYON flights, Liberty’s managers allowed NYONair personnel, particularly NYONair’s chief executive officer, to influence core aspects of the operational control of those flights.
- Ineffective safety management at both Liberty Helicopters Inc. and NYONair resulted in a lack of prioritization and mitigation of foreseeable risks.
- Liberty Helicopters Inc. and NYONair exploited the exception at Title 14 Code of Federal Regulations 119.1(e)(4)(iii) allowing aerial photography flights to be operated under Part 91, thereby avoiding the additional Federal Aviation Administration requirements and oversight that apply to commercial air tours conducted under either Part 135 or Part 91 with an air tour letter of authorisation.
- The Federal Aviation Administration principal operations inspector assigned to oversee Liberty Helicopters Inc. did not conduct additional surveillance of Liberty’s operations after being made aware of its FlyNYON flights and failed to ensure that Liberty was appropriately managing the risks associated with the significant change in operations.
- Because the Federal Aviation Administration (FAA) continues to allow passenger revenue operations to be conducted under Title 14 Code of Federal Regulations Part 91 - some of which, like the FlyNYON flight operations, transport thousands of passengers annually - the FAA must provide inspectors with sufficient guidance to pursue more comprehensive oversight with regard to potential hazards they observe and to ensure that operators sufficiently mitigate risks.
- Although the certification basis for the accident helicopter’s fuel shutoff lever did not require protection from inadvertent activation due to external influences, a design modification that includes such protection could enhance safety more effectively than continued reliance on operational measures.
The Probable Cause of the accident was determined by the Board as “Liberty Helicopters Inc.’s use of a NYONair-provided passenger harness/tether system, which caught on and activated the floor-mounted engine fuel shutoff lever and resulted in the in-flight loss of engine power and the subsequent ditching".
Three Contributory Factors to the accident were identified as:
- Liberty’s and NYONair’s deficient safety management, which did not adequately mitigate foreseeable risks associated with the harness/tether system interfering with the floor-mounted controls and hindering passenger egress.
- Liberty allowing NYONair to influence the operational control of Liberty’s FlyNYON flights.
- The Federal Aviation Administration’s inadequate oversight of Title 14 Code of Federal Regulations Part 91 revenue passenger-carrying operations.
Two Contributory Factors to the severity of the accident were also identified:
- the rapid capsizing of the helicopter due to partial inflation of the emergency flotation system.
- Liberty and NYONair’s use of the harness/tether system that hindered passenger egress.
A total of fourteen Safety Recommendations were made as follows:
- that the Federal Aviation Administration modify the supplemental passenger restraint system (SPRS) approval process to:
- require letter of authorisation (LOA) applicants to specify a need for and the intended use of an SPRS for each aircraft;
- require the Federal Aviation Administration to evaluate and review, for each specified aircraft, the need for the SPRS on that aircraft for all intended uses; all SPRS design, manufacture, installation, and operational considerations, including, at a minimum, the potential for passengers to become entangled during emergency egress; the adequacy of passenger emergency egress briefings; and the potential for the SPRS to interfere with aircraft controls; and
- ensure that each LOA lists the specific aircraft on which the holder is authorised to use an SPRS. [A-19-24]
- that the Federal Aviation Administration, until the supplemental passenger restraint system (SPRS) approval process as recommended in Safety Recommendation A-19-24 is implemented, prohibit the use of SPRS for passenger-carrying doors-off operations. [A-19-25]
- that the Federal Aviation Administration review the activation system designs of Federal Aviation Administration-approved rotorcraft emergency flotation systems for deficiencies that may preclude their proper deployment, such as a lack of a means to identify high pull forces on manual activation handles or inadequate guidance on the intended use of the activation system, and require corrective actions based on the review findings. [A-19-26]
- that the Federal Aviation Administration revise Miscellaneous Guidance 10 in Advisory Circular (AC) 27 and AC 29 to include design objectives for emergency flotation systems that consider human factors design objectives, such as activation handle pull-force characteristics; provisions for clear, unambiguous, and positive feedback to pilots to indicate that the float system was successfully deployed; and inspections to ensure that an installation of a manual activation system does not preclude a pilot’s ability to deploy the floats, as designed, after it has been fielded. [A-19-27]
- that the Federal Aviation Administration require all commercial air tour operators, regardless of their operating rule, to implement a safety management system. [A-19-28]
- that the Federal Aviation Administration revise Title 14 Code of Federal Regulations 1.1, “General Definitions,” to include definitions for the terms “aerial work” and “aerial photography” that specify only business-like, work-related aerial operations, as originally intended. [A-19-29]
- that the Federal Aviation Administration revise Order 8900.1, Flight Standards Information Management System, to include guidance for inspectors who oversee Title 14 Code of Federal Regulations (CFR) Part 91 operations conducted under any of the 14 CFR 119.1(e) exceptions to identify potential hazards and ensure that operators are appropriately managing the associated risks. [A-19-30]
- that the Federal Aviation Administration develop and implement national standards within Title 14 Code of Federal Regulations (CFR) Part 135, or equivalent regulations, for all air tour operations with powered airplanes and rotorcraft to bring them under one set of standards with operations specifications, and eliminate the exception currently contained in 14 CFR 135.1. [A-19-31]
- that Airbus Helicopters modify the floor-mounted fuel shutoff lever in AS350-series helicopters to protect it from inadvertent activation due to external influences. [A-19-32]
- that the Federal Aviation Administration, after the actions requested in Safety Recommendation A-19-32 are completed, require owners and operators of existing AS350-series helicopters to incorporate the changes. [A-19-33]
- that the Federal Aviation Administration develop guidance on how to identify intoxicated or impaired passengers, and distribute it to operators who carry passengers for hire under Title 14 Code of Federal Regulations Part 91 and Part 135. [A-19-34]
- that the European Union Aviation Safety Agency, after the actions requested in Safety Recommendation A-19-32 are completed, require owners and operators of existing AS350-series helicopters to incorporate the changes. [A-19-35]
- that Liberty Helicopters Inc. establish a safety management system. [A-19-36]
- that Liberty Helicopters Inc. train its employees to identify signs of impairment and intoxication in passengers and to deny those passengers boarding, when appropriate. [A-19-37]
The Final Report of the Board was adopted on 10 December 2019 and subsequently published.