Following the death of an airline employee in December and another major injury, the Federal Aviation Administration (FAA) issued a safety advisory to airlines on Friday in an effort to prevent further occurrences.

The FAA reiterated in the safety notice that “it is critical for workers to remain clear of operating engines until they are shut down.”

The alert comes as questions arise about U.S. aviation safety after a series of troubling near-miss incidents. The FAA has said it will hold runway safety meetings at 90 airports over the next few weeks.

In December, a ramp agent was fatally injured at Montgomery Regional Airport in Alabama when the worker was sucked into an engine of an American Airlines (AAL.O) regional carrier flight parked at the gate.

The flight was operated by Envoy Air, a wholly-owned subsidiary of American Airlines and the worker was employed by Piedmont Airlines, another American subsidiary.

The Occupational Safety and Health Administration issued Piedmont Airlines a citation for one serious violation in June for exposing ground crew workers to ingestion hazards while performing aircraft marshalling, wing-walking and baggage-handling tasks.

Piedmont faces $15,625 in proposed penalties, the maximum allowed by law. The company has contested the findings before the independent Occupational Safety and Health Review Commission.

Piedmont said on Friday its policies and procedures “are compliant with FAA requirements and actively address all the concerns outlined in the citation.”

In another event, a wing walker sustained a serious injury when an aircraft was being repositioned, the FAA said.