The deranged man who sowed chaos on a Frontier Airlines flight out of Puerto Rico — allegedly attacking a flight attendant and attempting to pry open exit doors — faces up to 21 years in prison over the incident.

Juan Gabriel Reyes, 51, of Chicago, forced Frontier Airlines Flight 3345 to divert to Miami on Sunday after he tried to open the exit doors of the Chicago-bound plane, according to the US Attorney’s Office in the Southern District of Florida.

Reyes also attempted to open the doors to the flight deck floor and attacked a fellow passenger before trying to choke an off-duty flight attendant.

It took crew members and a former MMA fighter to subdue Reyes, with the plane stopping in Miami, where he was arrested.

Video posted on social media shows how Josh Longood, a Brazilian jujistu black belt, helped restrain the man as crew members bound the out-of-control passenger’s hands with zip ties.

“I just grabbed him, restrained him as safely as possible, kind of just really put him in his row, and laid him down, kind of framed against him, controlled his hands and his feet,” Longood told CBS News.  

“It was like holding a kid down throwing a tantrum,” he added.  

Frontier Airlines confirmed the incident in a statement to The Post, adding that the flight continued on its journey to Chicago a few hours after the disturbance.

Reyes was charged with interference with flight crew members and attendants and assault within maritime and territorial jurisdiction, prosecutors said. 

He could also face more than $40,000 in fines from the  Federal Aviation Administration.   

The US Attorney’s Office in the Southern District of Florida declined to provide further comments on the case. 

Sunday’s incident was only the latest account of unruly passengers forcing planes to divert their trips midflight. 

The FAA has investigated about 687 reports of unruly passengers so far this year.