Inverter lockout cited in ZeroAvia hydrogen test bed accident

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The crash-landing of a hydrogen-powered Piper PA-46-350P Malibu Mirage test bed operated by hydrogen-electric aircraft developer ZeroAvia last year resulted from an inverter lock-up, the report says report published by the British Air Accident Investigation Branch (AAIB). ). Investigators found that “the loss of power occurred during an interruption of electrical power when, as part of the test procedure, the battery was selected with the intention of leaving the electric motors only powered by the hydrogen fuel cell During this outage, the windmill propeller generated a voltage high enough to operate the inverter protection system, which blocked power to the motors.

Attempts to restart the system failed and the plane, which was flying as part of ZeroAvia’s Project HyFlyer I flight test program, was badly damaged when it landed outside the airport and hit a ditch and a hedge. As previously reported by AVweb, the accident took place on April 29, 2021, near Cranfield Airport. No fire after the accident occurred and no one was injured in the accident.

Issues identified in the AAIB report include the positioning of the pilot display unit, which was obscured by the pilot’s hand on the throttle, as well as warning and caution indications that had no attention property. The AAIB further concluded that “sufficient ground testing had not been performed to determine the effect of windmill propeller back-voltage on the inverter protection system” and that the procedures emergency procedures established for the situation were ineffective. In addition, he found that a power loss due to an inverter lockout had occurred on several previous flights and had not been properly investigated and risk assessments n had not been examined following these thefts.

The AAIB’s safety recommendations relating to the accident call on the UK Civil Aviation Authority (CAA) to take action such as developing guidance on the use of existing materials related to the design and placement of controls and displays on experimental aircraft, clarifying “the scope of projects deemed suitable for execution” under experimental conditions and requiring independent file review for aircraft operated under experimental conditions. The AAIB also recommended that the CAA require persons designated as competent persons under CAP1220, Operation of Aircraft in E Conditions, to have the knowledge, skills, experience and ability to manage and supervise the registered experimental test program and that the CAA “improves guidance for the competent person and principal test pilot in the organization, management and conduct of the flight of an experimental aircraft project.

“While the report does not make specific recommendations for ZeroAvia in its findings, many of the issues identified in the report were also noted in our internal investigation and have subsequently been firmly resolved,” the company said. said in a press release. “We have incorporated key learnings into both our organizational culture and structure, as well as our future technical designs.” ZeroAvia also noted that it has established a Safety and Security Review Committee as well as a Safety Management System, which includes event reporting, investigation and corrective actions since the accident.

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