SINGAPORE - The two-hour flight from Surabaya to Singapore is not a particularly challenging one, say pilots familiar with the route.

"It's a common route for flights going to Jakarta, Lombok and other places as well and while it is true that weather conditions are more extreme these days, it is not significantly bad for this particular flight path" said an experienced pilot who asked not to be named.

Said another pilot: "Bad weather means we have to be more cautious during the flight of course and be prepared to make changes to the flight route where necessary, to avoid turbulence or other weather-related issues."

The pilots of AirAsia Flight QZ8501, which was travelling from Surabaya to Singapore on Sunday morning, had asked to climb higher to avoid bad weather about an hour into the flight.

The aircraft which was carrying 155 passengers and seven crew members lost contact with air traffic control shortly after that and is believed to have crashed.

Most of the passengers are Indonesian while one Singaporean was said to be on board.