According to a CNN transportation analyst, the plane’s landing gear did not appear to have been turned off when it crash-landed on the runway, according to video footage of Sunday’s disaster.

Mary Schiavo, a former U.S. Department of Transportation inspector general, said one of the engines had failed or the plane’s indicators could have been damaged. Another possibility, she said, was that the pilot was attempting a “go-around,” meaning the pilot wanted to abort the landing and circle in the air again to check if the gearbox was working.

Jeju Air Flight 7C 2216, listed on flight tracking website FlightAware as a Boeing 737-800, was carrying 181 people (175 passengers and six crew) from Bangkok to Muan International Airport.

The tragedy occurred during a busy leisure travel season, noted Schiavo, who spoke from Chiang Mai, Thailand.

“Everywhere is full of families celebrating the holidays. So we can bet that this flight was most likely fully booked,” she said.

While Jeju Air is a popular low-cost airline, South Korea generally has a high aviation safety rating, Schiavo said. South Korea is rated Category 1 in the US Federal Aviation Administration (FAA) International Aviation Safety Assessment Program.

The aviation industry is booming in both South Korea and Thailand and throughout Southeast Asia, so regulators need to keep pace with the growth, Schiavo said.