Great Lakes Airlines, a once-robust regional carrier providing passenger service between Denver International Airport and airports across the West and Midwest, suspended all of its scheduled flights as of Tuesday .

The shutdown left passengers at DIA holding useless tickets to Cheyenne and Salina, Kan., and stranded some travelers in Telluride, which has no other commercial carrier. Great Lakes also connected Los Angeles International Airport and Phoenix Sky Harbor International Airport to the Arizona cities of Prescott and Page.

“Although we are ceasing flight operations, it is important to note that the company has not entered bankruptcy and will continue to operate certain segments of the business,” the airline said on its website.

Great Lakes Jet Express — the airline’s partnership with Aerodynamics Inc. — will continue to fly, carrying passengers between Denver and the South Dakota cities of Pierre and Watertown.

The news marks a steep fall for the Cheyenne-based airline that once had 1,600 employees, more than 60 aircraft and dozens of destinations across the U.S.

But, for years, Great Lakes Airlines has reported problems hiring and retaining pilots and has, as a result, drastically cut its number of routes.

“It’s just plain, fundamental draining of availability of pilots,” said Great Lakes CEO Doug Voss, who founded the airline in the late 1970s. “At the end of the day, it’s about the pilot-supply issue and how government is managing the consequences of it.”

Voss also blamed the dearth of pilots on the rising costs of learning how to fly.

“We will probably be shrunk down to 40 employees,” he said. “It could even become smaller than that.”

Shares in the publicly traded company closed at 15 cents Tuesday.

Voss said he is exploring the possibility of using his planes for cargo transport and didn’t rule out the possibility of one day resuming passenger service.

At one point, Great Lakes also had a presence at Minneapolis/St. Paul International Airport and a long list of destinations, along with partnerships with major airlines. But, recently, the carrier has scaled back, in part because of stricter rules for pilots and because their reputation was tarnished by cancellations, said James Simmons, who teaches aviation and aerospace science at Metropolitan State University of Denver.

“This is what’s been happening across their system, and they’ve lost most of their Essential Air Service routes,” he said, referencing the federal program that offers subsidized flights to small communities that otherwise wouldn’t have passenger-plane service. “They’ve been having trouble for a long time. Most of their revenue used to come from Essential Air Service.”

In 2015, the regional carrier entered into a priority-hiring agreement with Metro State’s aviation program to help direct entry-level pilots to the airline’s hiring pipeline. But that pipeline has been dismantled.

“The bridge program was suspended about 18 months ago, when GLA lost a lot of their Essential Air Service contracts,” said Kevin Kuhlmann, associate chairman of Metro State’s aviation and aerospace science department.

Kenny Maenpa, airport manager at Telluride Regional Airport, said ski season is just wrapping up in the southwest Colorado resort town and the suspension of service couldn’t have come at a worse time. He called the news an “inconvenience, frustrating passengers that have booked flights out of Telluride over the next two weeks.”

Maenpa said he found out about Great Lakes’ decision Monday, just after the carrier’s last flight left at about 3:30 p.m. Since the airline restarted service to Telluride in December 2016, it had been offering about 14 flights a week, most of them to Denver.

“Telluride Regional Airport serves a world-class resort that had 30,000 passenger enplanements on U.S. Airways, Continental and United/Great Lakes 10 years ago. In 2017, the airport had only 3,700 enplanements with Great Lakes Airlines,” Maenpa said, blaming the pilot shortage for the decline. “This commuter airline that serves a very critical need to small communities is a casualty of that.”

Colorado Flights Alliance, an economic development organization for the Telluride area, said the nearby Montrose Regional Airport still handles the bulk of air traffic into that part of the state — more than 350,000 seat annually — so passenger plane service overall is largely unaffected. They also said they were working to assist the 50-75 customers who booked flights with Great Lakes to Telluride, urging them to rebook through Montrose.

PenAir, an Alaska-based Essential Air Service airline, also cited the pilot shortage when it stopped flying from DIA last year.

DIA spokeswoman Mindy Crane said Great Lakes carried fewer than 45,000 passengers from the airport in 2017.

“Cheyenne and Telluride will now be unserved from Denver,” Crane said. “Of course, we are very disappointed to lose this service as one of (the airport’s) strengths is our regional connectivity which, in turns, helps to feed other domestic and international flights. We will be talking to other airlines about the possibility to add service … to both of these airports.”