Allegiant Air Flight 815 had just departed North Carolina on Dec. 3 with 94 passengers bound for St. Pete-Clearwater International Airport when an alarming gray haze began to fill the cockpit and passenger cabin.
Pilots declared an emergency, telling the tower to notify fire rescue crews "to roll the trucks." The haze dissipated on landing at Raleigh-Durham, N.C., and the problem was traced to a malfunctioning air-conditioning system.
Mechanics knew the aircraft quite well: This was the fourth emergency landing by the same aircraft in little more than a month.
The emergency landings by the MD-88 — tail number 403NV — occurred from Oct. 25 to Dec. 3 on flights headed to Florida, all after reports of smoke or fumes in the aircraft. Some of the incidents may have been because of the same recurring problem, according to interviews and Federal Aviation Administration records.
The aircraft also made an emergency landing in August due to engine trouble that did not involve a report of smoke.
Industry veterans say such a high number of incidents for one aircraft in such a short period of time is exceptionally rare, and the incidents will undoubtedly raise renewed concern about Allegiant's maintenance operations.
During an Oct. 25 emergency landing on a flight departing Youngstown, Ohio for Sanford, outside Orlando, an FAA report filed by Allegiant noted, "Smoke was so thick that the flight attendants in the back of the airplane could not see the front."
John Cox, a St. Petersburg resident who is a former U.S. Airways pilot and a former safety official at the Air Line Pilots Association, said it is rare to see one plane make so many emergency landings.
"To have one aircraft experience a high number of smoke events, that is very, very unusual," Cox said. "I have seen smoke or fume events reoccur. But if they had repeated smoke events in a five or six week period, this would be very unusual and would be right at the edge of anything I've seen in my career."
Allegiant has maintained the Las Vegas-based airline has one of the best safety records in the industry. A spokeswoman with the airline said Friday that company officials could not comment on this story because they were busy dealing with a snow storm in the eastern United States.
Allegiant, a budget airline with a fleet of more than 80 aircraft, was responsible for about 95 percent of the record 1.6 million passengers who used the St. Pete-Clearwater airport last year, making a key player in the area's growing tourism industry.
Allegiant's chief operating officer Steve Harfst abruptly resigned a week ago after just 13 months on the job. Some analysts suggest the resignation was forced and is a result of highly publicized incidents involving Allegiant aircraft. The airline and Harfst will not comment on such speculation.
Those incidents include an additional five emergency landings by Allegiant aircraft during the last week of 2015.
Allegiant announced late Thursday that it was promoting its senior vice president of planning, Jude Bricker, to COO as Harfst's replacement.
Chris Moore, chairman of the Teamsters Aviation Mechanics Coalition, discovered the four emergency landings for the one aircraft while taking reports from Allegiant crew members on behalf of the pilots' union, the Airline Professionals Association Teamsters Local 1224.
The Tampa Bay Times confirmed those four by examining "service difficulty reports," or SDRs, Allegiant filed with the FAA. And the newspaper discovered the August emergency in those records. It does not appear any passengers or crew were injured in the incidents.
Moore is compiling a report on the airline's maintenance issues for the Teamsters, which has been at odds with Allegiant management over bitter contract negotiations. The airline has blamed the union for raising unfounded safety concerns as a ploy in negotiations.
Moore said in an interview that the issues with the one aircraft raise serious questions on how well Allegiant maintains its fleet. Moore said the FAA has placed Allegiant under increased scrutiny due to these issues, though the agency won't confirm that.
"I'm sure the FAA is seeing what we are and asking, 'What's going on?'" Moore said.
He said he believed, though he had not been able to confirm, that the four emergencies may have involved a recurring problem that was not properly diagnosed or which recurred after inadequate repairs.
FAA spokesman Ian Gregor declined to comment specifically about the aircraft with the multiple problems, though he said the FAA is investigating incidents reported in the media.
According to Moore and FAA records on the aircraft (all flights landed at the city from which they departed), these are the incidents:
•On Oct. 25, Allegiant Flight 607 departed Youngstown for Sanford when the crew smelled smoke at rotation, the moment when an aircraft begins to lift off the runway. Flight attendants then reported smoke coming from a fan that delivered air into the cabin from the plane's air system. Air-conditioning was turned off and the aircraft safely landed.
• On Oct. 30, Flight 730 had just departed Concord Regional Airport in North Carolina bound for Fort Lauderdale when flight attendants reported smoke in the cabin. Mechanics replaced the oil filter and an O-ring on an auxiliary power unit, and found a leak in the hydraulic system.
•On Nov. 15, shortly after Flight 715 departed Owensboro-Daviess County Regional Airport in Kentucky for Sanford a bathroom smoke detector alarm began sounding. The FAA report said "there was a haze in the cabin with a smoke smell." The problem was diagnosed as occurring in an air-conditioning system.
• On the Dec. 3 flight to St. Pete-Clearwater, the problem was again tied to the air-conditioning.
• On Aug. 17, the plane suffered engine difficulties at 16,000 feet and made an emergency landing. No report of smoke occurred on that flight, and records do not show where the plane landed, its destination nor city of departure.
FAA records also show the aircraft's crew on Dec. 15 experienced the smell of evaporating oil in the cockpit, but FAA records indicate the crew did not make an emergency landing for that event.
Cox said airlines usually will take an aircraft out of service after repeated problems to conduct a detailed examination. He said mechanics can sometimes fix a problem on an aircraft only to later discover the real issue has been missed.
Greg Marino is an aviation mechanic with more than three decades of experience who said he quit the airline's Sanford maintenance operation in October after just two weeks because of what he viewed as Allegiant's poor maintenance culture. Allegiant disputes his characterization.
Marino said when he worked at US Airways, repeat problems on an aircraft would be quick reason to ground it.
"We wouldn't have gotten three chances," Marino said, referring to the four emergency landings in a month. "We may have gotten two, meaning the airplane would have been grounded ... This is a clear indication of an experience level that is going to cause a big problem for Allegiant."
Times researcher John Martin contributed to this report. Contact William R. Levesque at levesque@Tampabay.com. Follow @Times_Levesque.