Air Ambulance Leaps into Air: Misrigged Flying Controls (Air Evac Lifeteam EC130T2 N894GT, Memphis, TN)
On 28 January 2018 air ambulance Airbus Helicopters EC130T2 N894GT of Air Evac Lifeteam was damaged in a hard landing after it inadvertently became airborne while on the elevated landing site at Memphis Regional Medical Center in Tennessee. None of the 4 occupants were injured but impact was hard enough to spread the skids, caused minor structural damage and set off the Emergency Locator Transmitter (ELT).
The 58 year old pilot pilot had 6267 hours total time, but only 9 on type. having completed a 5 day EC130 course at Airbus in early November 2017. His last proficiency check was 11 days earlier. According to the NTSB:
While on a long final approach to the heliport, there was a left crosswind present and he had to reduce collective pitch control friction three times in order to move the collective as fast as he felt he needed to. He brought the helicopter to a hover as he reached the heliport, then turned the helicopter to the right and landed.
After landing, he started the after-landing portion of the checklist, then turned the throttle twist grip on the collective from “FLY to “IDLE,” believing [our emphasis] that he had engaged the collective lock.
He then turned the horn mute switch to mute, grabbed the cyclic pitch control with his left hand, and reached for the clock start button with his right hand.
As he was reaching for the clock button, the collective “popped up,” and the helicopter became airborne. He immediately grabbed the cyclic with his right hand, the collective with his left hand, and twisted the twist grip to “FLY.” The helicopter then landed hard, and the emergency locator transmitter (ELT) activated. After exiting the helicopter, the flight nurse advised the pilot that there was damage to the sheet metal of the helicopter.
CCTV footage showed the occurrence:
The Safety Investigation
Examination of the helicopter revealed minor damage. The skid type landing gear was spread out, and both landing gear cross tubes were deformed. The forward belly panels were dented from contact with the forward landing gear cross tube, and the aft closeout panels were dented from contact with the aft landing gear cross tube.
Investigators had access to engine data from the Safran Arriel 2D engine’s full authority digital engine control (FADEC) system stored on an engine data recorder (EDR). The helicopter was also equipped with an Appareo Vision 1000 unit, which records images, audio and limited flight data onto a removable SD memory card. NTSB comment that:
Review of the onboard video depicted a series of events consistent with the pilot’s statement.
Review of EDR data indicated that, during the incident portion of the flight, the recorded transducer position for the collective showed the collective rising from an unlocked position with the helicopter’s engine transitioning from “Idle” to “Flight.”
The EC130 can be converted between a dual-pilot configuration (e.g. for training) to a single-pilot configuration. Two days earlier, a mechanic at the Air Evac base at Jackson, Tennessee had removed the right seat dual controls to reconfigured the helicopter for single-pilot operation. When an FAA inspector examined the aircraft…
The collective was placed in the full-down position to attach a spring scale to the twist grip to measure the force required to pull it through its upward travel; however, once the mechanic removed his hand from the collective prior to attaching the spring scale; the collective immediately climbed unassisted to approximately the mid-travel position, indicating that the collective was improperly balanced for the single-pilot configuration. It was determined that the spring force was much greater (approximately twice that required) than it should have been in the upward direction.
The maintenance manual describes the process for “Adjustment – Collective Stick Balance” (extracts are within the Public Docket). The implication of this investigation finding is that the rebalancing was either not conducted when the dual controls were removed or that it was not completed successfully.
The operator has changed their abbreviated checklist for the EC130T2, so that the first item after landing is to roll the twist grip to “IDLE” and then place and confirm the collective pitch is “Down/locked.” A “NOTE” has been added to
“Visually and verbally confirm collective is locked.”
UPDATE 3 March 2022: NTSB Probable Cause
The pilot’s failure to lock the collective pitch control after landing, and the mechanic’s failure to properly balance the collective pitch control after converting the helicopter to a single-pilot configuration, which resulted in an uncommanded collective movement and subsequent hard landing.
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You might also find these safety / human factors resources of use:
- James Reason’s 12 Principles of Error Management
- Back to the Future: Error Management
- Aircraft Maintenance: Going for Gold?
- Critical Maintenance Tasks: EASA Part-M & -145 Change
- This 2006 review of the book Resilience Engineering by Hollnagel, Woods and Leveson, presented to the RAeS by Aerossurance’s Andy Evans: Resilience Engineering – A Review and this book review of Dekker’s The Field Guide to Understanding Human Error: The Field Guide to Understanding Human Error – A Review.
Aerossurance worked with the Flight Safety Foundation (FSF) to create a Maintenance Observation Program (MOP) requirement for their contractible BARSOHO offshore helicopter Safety Performance Requirements to help learning about routine maintenance and then to initiate safety improvements.