Being on-time is a nice feature in an airline. Late flights are easily one of the most annoying parts of traveling. So, knowing which airlines will get you where you're going at the promised time is no small thing.
OAG has just released its On-time Performance (OTP) Report for September 2018, and we selected only airlines with flights of over 3,000. It has determined that for last month, Bangkok Air (Thailand) was Southeast Asia's most on-time airline . Bangkok Air finishes April with a stunning 93.1% of flights arriving on time, followed by Garuda Indonesia on #2 with 90.5% OTP, and Thai AirAsia on #3, with 85.10% OTP.
Seasia gathered the OTP report for Southeast-asian-based major airlines (with 3,000 flights and above) for September 2018. Here's the result:

The definition of on-time performance, or OTP, is flights that arrive or depart within 14 minutes and 59 seconds of their scheduled times.
OAG has the world’s largest network of air travel data, including the definitive schedules database of more than 900 airlines and over 4,000 airports. With the most extensive flight status information database in the market, OAG handles more than 57 million records of flight status updates per year, processes 1.4 billion requests and continues to deliver in excess of 35 million dynamic flight status updates daily.
source: OAG.com