An Allegiant Air flight that departed the Orlando area made an emergency landing in Ohio a week ago after the pilot reported a fire in one of the aircraft's engines at 14,000 feet.

Flight 636 with 163 passengers and crew was about 10 minutes from landing in Dayton, Ohio, just before noon when a cockpit warning light indicated a fire in the aircraft's right engine, according to an internal Allegiant memo obtained by the Tampa Bay Times.

Pilots immediately deployed the engine's fire-suppression system, telling air traffic controllers, "We have an engine failure and a fire."

"We're declaring an emergency," the pilot said, according to an air traffic control recording of the incident. "We have a right engine fire indication and power loss. So yeah, if we could get to the airport as soon as possible, please."

The 29-year-old McDonnell Douglas MD-83 landed safety in Dayton International Airport at 12:03 p.m. An inspection of the engine revealed what the memo described as signs of fire/high heat involving an engine generator and engine cowling.

This is the second incident involving an engine of an Allegiant aircraft this month. On March 4, another MD-83 aborted takeoff at St. Pete-Clearwater International Airport after an engine failure that left debris on the runway.

The two engine failures may underscore why Allegiant is working to eliminate all MD-80 series aircraft from its fleet by the end of 2019 because the aircraft require more maintenance and are more prone to mechanical problems. The airline's website says it operates 48 MD-80 series aircraft in a fleet of 85 planes overall.

Eliminating the MD-80s is a critical goal for Allegiant because the older planes are the source of many of the airline's operational woes that disrupt its schedule, from emergency landings to canceled and delayed flights. Some of those emergencies have occurred at St. Pete-Clearwater International Airport, where Allegiant accounts for 95 percent of passenger traffic.

Previous coverage: Thousands of people flew Allegiant last year thinking their planes wouldn't fail in the air. They were wrong.

Officials of Allegiant, a Las Vegas-based budget airline, said they are still investigating the latest incident and could not say the cause of the engine failure. The Federal Aviation Administration also has been notified.

An engine fire is not the sort of run-of-the-mill, flight malfunction that causes delays for all U.S. airlines each and every day, aviation mechanics say.

"It's not common at all," said John King, a retired aviation mechanic with more than 30-years experience. "Even a false indication of a fire is rare… If you lose one engine to a fire, you have one engine left. That's not a very cheery situation."

An internal memo, circulated among Allegiant operational teams as part of Allegiant's routine safety regimen, appeared to downplay the incident by saying pilots shut down the engine and noted the aircraft flew on one engine for "approximately 1 minute."

But a review of the air traffic control recording shows the aircraft flew on one engine for at least eight minutes, and the pilots clearly indicate the engine failed.

Allegiant spokeswoman Hilarie Grey indicated the memo was based on the best information available at the time.

"Investigation is in progress, and as you know, takes time," Grey said in an email, indicating the memo pointed to "nothing mysterious."

Contact William R. Levesque at levesque@tampabay.com. Follow @Times_Levesque.