By S.L. Fuller | December 21, 2017
With safety at the forefront of all rotorcraft designs and associated materials, unfortunately things can go wrong amidst the complexities of operating a helicopter. 2017 brought on a few high-profile events that we're keeping on our radar. You can find these highlights and more in R&WI's January 2018 issue.
As of publication, the NTSB has not reported anything final about the investigation into Bell's crashed 525. In fact, the NTSB thus far has refused to answer questions about its factual investigation findings and hasn’t issued any official updates since its preliminary report in July 2016. When R&WI inquired to Bell in September, we were told the investigation is essentially at the finish line.
What we do know about the 525’s 2016 accident that left its two test pilots dead is that the prototype experienced rotor system vibration and frequency resonance in its airframe and flight control system, seconds before the aircraft broke up in flight. Three people that were briefed by the FAA told R&WI in March that data analysis of a recovered flight-test recorder, telemetry from the accident aircraft and simulations conducted by Bell for the safety board indicate the onset of the vibration and the subsequent response by the No. 1 Relentless prototype. Analysis of the aircraft's cockpit voice recorder was not possible because the device was not powered during the July 6, 2016, test flight. One official said FAA guidance permits a CVR to be unpowered during a test flight.
The industry does, however, have closure regarding the Leonardo AW609’s fatal 2015 crash. That final report was issued in May by the National Agency for Flight Safety, known by the Italian abbreviation ANSV. Like the NTSB, the ANSV was dealing with a civil fly-by-wire-aircraft — this one a tiltrotor.
The ANSV concluded the No. 2 AW609 type broke up over Santhià, Italy, after the blades of its right- and left-hand prop rotors all flapped and struck the wings’ leading edges during the test at the aircraft's design dive speed of 293 kt (calibrated airspeed). The blade strikes severed hydraulic lines, triggered a fire and led to the in-flight breakup that killed test pilots Herb Moran and Pietro Venanzi. The pilots already had performed dives that day of 303 and 295 kt.
Among the safety recommendations included in report, the ANSV calls on the FAA and EASA “to verify that the aerodynamic behavior of the aircraft at high-speed conditions will be reviewed, if necessary making use of wind tunnels tests in addition to updated models and simulations that can be representative of the complex flight conditions of this peculiar aircraft.”
The ANSV also called on those agencies “to verify that the control laws of the aircraft will be reviewed in the management of the extreme flight conditions in which the aircraft could possibly fly. That verification should be addressed to ensure the effectiveness of the flight controls inputs given by the pilot avoiding the possibility of unexpected and un-commanded coupling effects.
In an investigation report that would both give closure and leave questions was final findings of the 2016 fatal Airbus EC225LP Super Puma crash. A new preliminary report was published in April, nearly a year after the main rotor separated from the CHC Helicopter Service-operated aircraft, causing it to fall out of the sky and kill 11 passengers and two pilots.
The Accident Investigation Board Norway (AIBN) said its probe pointed to a fatigue fracture in the main rotor gearbox as the cause of the crash. But it was unknown at that point what caused the fracture. Investigators’ focus was put on design and subsequent certification, as they claim the fracture was unlike anything expected during the design and certification processes — and happened in a way that was unlikely to be found during maintenance.
The AIBN noted similarities between the 2016 tragedy and the 2009 crash of a Eurocopter AS332L2 Super Puma in the North Sea. In what was also a tragedy, the main rotor gearbox caused the main rotor to break away from the aircraft, resulting a crash that left both crewmembers and 14 oil platform workers dead, according to the U.K.’s Air Accidents Investigation Branch. A warning of possible gear failure was deployed in the 2009 crash.
However, as of publication, no final conclusions have been drawn on the 2016 crash.
Although headlines have generally said the oil and gas industry is not interested in putting full trust in the EC225LP at this time, the aircraft is not banned from operation. In July, the civil aviation authorities of the U.K. and Norway said they planned to lift operation restrictions on the 225LP and 332L2 — so long as some measures are met. EASA had released the Super Puma back into service October 2016. But the U.K. and Norway wanted operators to perform checks, modifications and inspections. Airbus also made some changes and modifications to the helicopter and maintenance.
An alternative to the Super Puma for offshore oil and gas operators could be the Sikorsky S-92. However, that aircraft type went through its own share of investigations in 2017.
To start the year off, Sikorsky told customers to immediately inspect their S-92s before next flight Jan. 10. The manufacturer was also reviewing health and usage monitoring (HUMS) data for S-92s at that time. That was prompted by a non-fatal incident that occurred in the last days of the previous December.
The U.K. took on the investigation and initially said the CHC-operated aircraft had onboard two pilots and nine passengers. During the event, it spun more than 180 deg to the right and rolled 20 deg to the left while landing on the rig more than 100 nm east of Aberdeen, Scotland. The S-92’s left main landing gear gouged the helideck on the Elgin Process, Utilities, Quarters rig before the pilots were able to land the aircraft. The failure appeared to be traced to a seized bearing in the servos. Just 4.5 flight hours before the accident, the aircraft’s health and usage monitoring system captured the first indication of trouble with the bearing. But detailed analysis did not reveal that until after the accident.
In March, Ireland’s Air Accident Investigation Unit was investigating the crash of an Irish Coast Guard CHC Helicopter S-92. Dublin-based R116, a search and rescue helicopter, lost contact with its base. There were four Coast Guard members on board. As of March 27, search crews were still looking for two of the bodies. From pieces of the S-92 that were recovered, it was surmised that that the tail hit the rocky surface of Blackrock Island.
This was reiterated in the investigator’s preliminary report, published in April. Also in that report is record of Honeywell admitting about its enhanced ground proximity warning system, “The lighthouse obstacle is not in the obstacle database and the terrain of the island is not in our terrain database.” The report omitted the firm that supplies Honeywell with the data. The investigation is, at press time, ongoing.