HONG KONG - Hong Kong airlines Cathay Pacific and Cathay Dragon are reportedly "deep cleaning" their aircraft less frequently.

The thorough cleaning operation, which currently takes three to four hours, has been cut from once per fortnight to once in three to four weeks, the South China Morning Post reported on Friday (Dec 30).

Parts of the aircraft most used by passengers, such as seats and toilets, are usually cleaned in between flights, but deep cleaning goes into the hard-to-reach areas such as under seat cushions.

Cathay Pacific and Cathay Dragon told SCMP they had faced challenges trying to adhere to their fixed 14-day cleaning schedule due to individual aircraft taking unplanned maintenance breaks or planes being swapped between short- and long-haul flights.

A Cathay Pacific passenger, who did not give his name, told SCMP that he used a hot towel to wipe all the surfaces on his business class seat on a flight to Singapore this year.

The wipe-down blackened the towel, he said, and he now does it for every flight.

An SIA spokesman told The Straits Times on Friday that deep cleaning for its aircraft takes place monthly.

"This involves maintaining and cleaning technical areas such as air vents as well as nuts and bolts," said the spokesman.

A 2014 study presented at the American Society for Microbiology showed that bacteria that cause vomiting and potent infections may be able to survive on aircraft surfaces for up to a week.