The chief operating officer of Allegiant Air unexpectedly resigned his post at the Las Vegas-based airline effective immediately, Allegiant announced late Friday.Steven E. Harfst, 52, a former Navy fighter pilot with nearly three decades of experience in the aviation industry, had worked at Allegiant for a little more than a year and had been the most prominent executive at the airline behind its CEO, Maurice Gallagher Jr.The resignation has repercussions in Tampa Bay with Allegiant flying about 95 percent of the passenger traffic at St. Pete-Clearwater International Airport, which flew a record 1.6 million people last year.In a brief statement, Allegiant provided no reason for his departure and Harfst declined to comment when reached on his cellphone."The company will use this leadership change as an opportunity to refocus on operational needs and areas for improvement," Allegiant said in a statement. "Allegiant is committed to operational excellence and looks forward to continued progress in this area."Gallagher, Allegiant's chairman and CEO, said, "We thank Steve for his contributions to Allegiant. We look forward to continuing his efforts to strengthen our operation."Harfst had been a staunch defender of Allegiant during 2015 at a time when the airline experienced a string of highly publicized maintenance issues and emergency landings. He has also had a leading role in negotiations with the airline's pilots union, which has hammered Allegiant's maintenance practices as being unsafe.At least four Allegiant aircraft flying to or from Pinellas were forced to make emergency landings in the last year, including three in a one-month period during the summer.Harfst has told reporters that the union is using safety as a ploy to better its negotiating position in talks for a contract.Harfst said in a September interview with the Tampa Bay Times at Allegiant's corporate headquarters that he thought the airline was one of the safest in the industry."To me, it's always about being safe because you never undermine or take for granted being safe," said Harfst. "We're not insensitive to the media attention when our operation doesn't do what it is supposed to do. But we hope and we think most of our customers recognize the value we give and our intent to do what's right for them."The departure comes at a time when Allegiant is earning high profits that have been boosted by lower fuel costs. On a percentage basis, the airline at one point late last year was the most profitable airline in the world with a 24 percent profit margin.Harfst's resignation comes a week after a Times article featured a former Allegiant mechanic's accusations that the airline employed bad maintenance practices at its Sanford operation. A majority of the airline's routes are to Florida, and Allegiant is seen as a critical driver of local tourism.Earlier this week, Allegiant announced it would offer twice-weekly flights between St. Pete-Clearwater and New Orleans starting June 3. That is the 50th city with scheduled Allegiant service with the Pinellas airport.Harfst joined Allegiant's board of directors and became its COO starting Jan. 1, 2015. He was the former COO of IndiGo Airlines based in New Delhi.In a Times interview, Harfst said airline consolidation forced larger carriers to run more efficiently, taking them out of the smaller markets now feeding Allegiant's bulging bottom line."I'd rather be lucky than good," said Harfst. "We're really happy about what has taken place in the industry. We like that. We see a lot of runway ahead of us when it comes to growth, and St. Pete is going to be the beneficiary of that."Harfst is no stranger to pressure in the workplace. In logging 1,600 hours as a fighter pilot in a 10-year career with the Navy, he made 227 carrier landings. He left the service in 1996.Times researcher Caryn Baird contributed to this report. Contact William R. Levesque at [email protected] or (813) 226-3432. Follow @Times_Levesque.