WASHINGTON, United States -- US regulators said Sunday they are investigating an incident in which a Texas airport worker was killed after being sucked into a passenger plane engine. A Delta flight had arrived in San Antonio, Texas from Los Angeles on Friday night and was taxiing to the gate with one engine on "when a worker was ingested into that engine," the National Transportation Safety Board (NTSB) told AFP in a statement. "The NTSB is continuing to gather information about the event," it said. The worker was employed by Unifi Aviation, a company the airline giant contracts with for ground crew operations, according to local media. Delta told San Antonio broadcaster KENS 5 that the company was "deeply saddened" by Friday night's events and that it is "cooperating with authorities as they begin their investigation." Unifi Aviation told the broadcaster the incident was "a tragic accident." "From our initial investigation, this incident was unrelated to Unifi's operational processes, safety procedures and policies," the company said. On Wednesday, regional carrier Piedmont Airlines was fined $15,625 by the Occupational Safety and Health Administration (OSHA), another regulatory body, for the death of a ground crew worker last year in a similar incident. "Proper training and enforcement of safety procedures could have prevented this tragedy," an OSHA official said. Piedmont is a subsidiary of carrier American Airlines.