The National Transportation Safety Board took a rare step Thursday by calling for an investigation into federal oversight of the largest commuter air service in Alaska.

An urgent safety recommendation calls for a third-party audit of how well the Federal Aviation Administration has been following its own policies in interactions with HoTH Inc. over the past few years.

Airlines under HoTH Inc. include Frontier Flying Service, Hageland Aviation Services, Inc. and Era Aviation, which do business as Ravn Alaska and Corvus Airlines. Six crashes have occurred under those operators since 2012.

NTSB spokesperson Clint Johnson said there are no other unresolved urgent recommendations in the United States, but this case is of "vital interest" to the board: "We felt that we couldn't wait until all investigations are complete," Johnson said.

The companies operate a combined 58 aircraft with about 1,200 operations each week, according to the NTSB. That composes the largest Part 135 operator in Alaska, which refers to companies under the main FAA regulations for commuter and on-demand aircraft services.

Since 2012, there have been a combined six crashes under the corporation's umbrella:

In the report released Thursday, the NTSB calls FAA oversight of the operators into question, particularly in the years preceding the St. Mary's crash and the one on the North Slope. Hageland’s risk assessment plan was improperly implemented, according to the report.

"Although the St. Mary's and Baldami accidents are currently under investigation, preliminary findings indicate that the inadequate risk assessment program may have played a role in both," the report states.

The NTSB investigation allegedly revealed flaws with the company's training and staffing practices.

"Employees acting as flight coordinators were not properly trained for the job,” and the director of operations for Hageland delegated those responsibilities to the improperly trained flight coordinators.

Where the FAA fell short, according to the report, is in knowing there was a problem and failing to act: the operators had a total of 11 instances of noncompliance, but no certificate action was taken.

The series of problems is enough for the NTSB to call for a comprehensive audit of both the regulatory compliance and operational safety programs in place at HoTH, Inc., and a review of FAA oversight of the company.

The audit "should include a review of inspector qualifications, turnover, working relationships between the FAA and operators owned by HoTH, Inc., and workload," the report states.

Inspectors should come from outside Alaska, the board said.

Even with the string of crashes and perceived need for improvements, NTSB spokesperson Clint Johnson said HoTH Inc. deserves credit for some steps it has taken to improve flight safety.

“One of the most monumental things they did is open an operational control center,” he said. “FAA and the operator have been very cooperative. That’s a step in the right direction.”

In a statement Thursday afternoon, the FAA says it’s already acting on some of the issues addressed by the NTSB.

“The FAA began increased surveillance of Hageland Aviation in 2011,” FAA officials wrote. “Even before the NTSB issued its recommendations, the FAA decided to send an audit team from outside Alaska to look at the carrier and the FAA’s oversight. The team, which has been on-site this week, consists of highly experienced inspectors with many years of experience auditing carriers and FAA certificate management team activities.”

According to the FAA, it will respond with 90 days to the NTSB recommendations after reviewing them.

FAA spokesperson Allen Kenitzer didn’t immediately respond to a request for comment on the statement Thursday.

Please watch Channel 2 and check for updates to this developing story.