Monroe County has temporarily grounded its three air ambulances after one of the Sikorski S76 helicopters made an emergency landing at Florida Keys/Marathon International Airport Thursday morning, according to the sheriff’s office.

The helicopter was on its way to transport a patient to HCA Florida Kendall Hospital when the crew noticed its landing gear wasn’t functioning and returned to base in Marathon, which is in the Middle Keys.

The pilot set the chopper on the tarmac around 5:30 a.m. with at least one of its wheels remaining retracted, according to the sheriff’s office.

The sheriff’s office maintains and flies all three of the helicopters under a program Monroe County calls Trauma Star. The medical crews on board are members of Monroe County Fire Rescue.

A video of the incident released by the sheriff’s office shows the aircraft setting down on some sort of block placed underneath it to compensate for the malfunctioning landing gear.

No one was injured, including the patient, and the helicopter didn’t have major damage, according to the sheriff’s office. The patient was taken to Kendall by a waiting ambulance, Keys Sheriff Rick Ramsay said.

“I want to thank and applaud the entire Trauma Star crew for doing an outstanding job to safely land this aircraft resulting in no injuries,” Ramsay said in a statement.

The sheriff’s office notified the National Transportation and Safety Board and the Federal Aviation Administration about the incident, said sheriff’s office spokesman Adam Linhardt.

Linhardt said all three Trauma Star helicopters were temporarily grounded so maintenance crews ensure the other two aircraft don’t have the same issues. The sheriff’s office expects to have them back in the air by Friday morning, Linhardt said.

The choppers are based at Marathon International Airport and Lower Keys Medical Center on Stock Island in the Lower Keys. Because the Keys’ three hospitals don’t have trauma units, the helicopters are a quick lifeline to anyone seriously injured or ill throughout the 120-mile long island chain.

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The sheriff’s office says crews that fly and maintain the aircraft remain continuously busy, with an estimated 1,400 flights annually to mainland hospitals — or about three to four flights a day.

Over the next two years, the aging Sikorski fleet is expected to be replaced by three Leonardo AW 139 helicopters, which are the same kind used by Miami-Dade County Fire Rescue. The $52-million replacement program was approved by Monroe County commissioners in March.