The US Federal Aviation Administration (FAA) has proposed a USD715,438 civil penalty against Allegiant Air (G4, Las Vegas McCarran), for "allegedly operating an aircraft on more than two dozen flights following improper engine maintenance", the regulator said in a statement dated June 12.

The FAA recounted that in October 2017, Allegiant asked it if it could deactivate a functioning MD-80 automatic reverse thrust system when the engine’s exhaust-gas temperature exceeded normal limits. The administration responded in December of that year that deactivating the system would be improper unless the system itself caused the excess temperature, because, it pointed out, the temperature exceedance could have other causes.

On April 13, 2018, the exhaust gas temperature of an Allegiant MD-88 engine exceeded normal limits while the plane was taking off from Roanoke in Virginia for Orlando Sanford, the FAA alleged in its statement.

When this occurs, the MD-80 maintenance manual calls for the automatic reverse thrust system to be turned off before the cause of the excess temperature is found and corrected and before the system is turned on again. Allegiant, however, did not determine the cause, the FAA said, instead deactivating the system the following day and installing an inoperative placard on it.

The carrier continued to operate the MD-88 on twenty-eight passenger-carrying flights between April 14 and April 22, 2018, without determining the cause of the excessive exhaust temperature, the agency added, concluding that as a result, it violated the terms of its FAA-issued operations specifications. The Nevada-based ultra-low-cost carrier now has thirty days after receiving the administration’s enforcement letter to respond.

Allegiant ended McDonnell Douglas operations when its last MD-83/8 flights took place on November 28, 2018. At the time of their retirement, Allegiant had operated sixteen MD-83s and three MD-88s. The fleet is now an all-Airbus operation consisting of thirty-seven A319-100s and fifty-two A320-200s.