It is not the airlines which decide which tests are necessary. It is the governments of the destination country. The airlines go by whatever rules, say, the USA wants if one is flying to the USA. But note this caveat from below: "The test used must (also) be authorized for use by the relevant national authority for the detection of SARS-CoV-2 in the country where the test is administered. "
Antigen test takes a couple hours or less to get results and can cost as low as 700 baht. PCR tests are much more expensive and can take a lot longer to get results. The airlines accept tests BASED ON what the destination country wants. For example, USA accepts EITHER the cheap, quick Antigen test or the much more expensive, time consuming PCR ('NAAT') test. For some reason, many travelers to the USA are not aware they don’t need the expensive, time-consuming PCR test.
Below are quotes from the USA cdc.gov website which url link is below.
“Test and Vaccination Documentation Requirements
You must be tested with a viral test that could be either an antigen test or a nucleic acid amplification test (NAAT). Examples of available NAATs for SARS-CoV-2 include but are not restricted to reverse transcription polymerase chain reaction (RT-PCR), reverse transcription loop-mediated isothermal amplification (RT-LAMP), transcription-mediated amplification (TMA), nicking enzyme amplification reaction (NEAR), and helicase-dependent amplification (HDA). The test used must be authorized for use by the relevant national authority for the detection of SARS-CoV-2 in the country where the test is administered. A viral test conducted for U.S. Department of Defense (DOD) personnel, including DOD contractors, dependents, and other U.S. government employees, and tested by a DOD laboratory located in a foreign country also meets the requirements of the Order.
Rapid tests are acceptable if they are a viral test that meet the requirements under the Order.
You can use a self-test (sometimes referred to as home test) that meets the following criteria: (NOTE: I omitted here these few paragraphs on the self-test. Go to the website to read. I wouldn’t recommend this, especially since the regular Antigen test will come from a hospital and is not expensive.)
What kind of info must be on the test results?
A test result must be in the form of written documentation (paper or digital copy). The documentation must include:
Type of test (indicating it is a NAAT or antigen test)
Entity issuing the result (e.g., laboratory, healthcare entity, or telehealth service)
Sample collection date
A negative test result must show the sample was taken no more than 3 days before the flight for air passengers who have proof of being fully vaccinated, or no more than 1 day before the flight if the air passenger is not fully vaccinated.
A positive test result for documentation of recovery from COVID-19 must show the sample was taken within the 90 days before the flight.
Information that identifies the person (full name plus at least one other identifier such as date of birth or passport number)
Test result
Before boarding a flight to the U.S., you will need to show a paper or digital copy of your test result for review by the airline and for review upon request by public health officials after you arrive in the U.S.
https://www.cdc.gov/coronavirus/2019-ncov/travelers/testing-international-
air-travelers.html
