An Allegiant Air flight out of Orlando-Sanford International Airport was forced to make an emergency landing on April 22 after it suffered a problem with a critical control surface that caused a worrisome vibration in the aircraft.
Flight 736 took off at 9:13 a.m. headed to Bangor International Airport in Maine with 173 passengers and crew. During the climb out of central Florida, the pilots reported vibrations with the airframe of the McDonnell Douglas MD-80, according to an internal Allegiant memo obtained by the Tampa Bay Times.
The crew, the memo said, "had concerns with the elevator control."
The captain of the flight declared an emergency and the flight returned to Orlando-Sanford, where it safely landed at 10:08 a.m. "No immediate corrective actions to policy, procedure or the training program were found to be needed," the email said.
The elevator controls the pitch of the aircraft, moving the aircraft's nose up and down and controlling what pilots refer to as the plane's "angle of attack." It's a control surface critical to flight as it is not a redundant system and a failure can lead to a crash. Manufacturers design the systems to essentially never fail.
Allegiant described to the Times several parts of the elevator mechanism that mechanics replaced after inspecting the aircraft. But the Las Vegas-based carrier refused to talk about the root cause of the elevator problem on Flight 736 or to talk in detail about the incident.
John Cox, CEO of aviation safety consultant firm Safety Operating Systems, said a plane's elevator can wear down. Because of how the system works on Allegiant's MD-80s, the pilot wouldn't necessarily notice the issue until the plane was airborne.
Cox said the incident does beg the question why maintenance had not spotted a problem with the mechanism before it caused a problem during a flight. "Any time you have a problem with a primary flight control, it's serious," he said.
An Allegiant flight suffered a jammed elevator in August 2015 after a mechanical failure of an elevator in Las Vegas. That plane's nose started to prematurely rise during the takeoff roll at 138 mph when the pilots managed to abort the takeoff. One of the pilots said afterward "had the aircraft become airborne, a serious accident would have resulted."
The FAA blamed an Allegiant maintenance contractor for the incident.
Allegiant is in the midst of replacing its fleet of aging MD-80s because the aircraft are prone to mechanical problems. Allegiant says the planes are safe, but mechanical difficulties lead to problems with the airline's operations and schedule. The airline will no longer fly MD-80s out of St. Pete-Clearwater, where Allegiant is responsible for 95 percent of passenger traffic, by the end of the year.
Times staff writer Malena Carollo contributed to this report.