PETALING JAYA (THE STAR/ASIA NEWS NETWORK) - Weather conditions around the Java Sea towards year end are known to be violent but not unmanageable, aviation experts said.

Retired pilot Datuk Jalil Mat Dom said thunderstorms in the region could be quite intense and pilots could ask for a change in their flight plans.

"During this time of the year, the weather can be very violent there. The intensity is quite big and also the area of the thunderstorm is widespread.

"I'm not sure how widespread the storm was, but it can affect the airways, which is why the pilot asked for a deviation," he said when contacted.

Datuk Jalil also said that pilots before departing an airport were aware of weather conditions as they were briefed by the meteorological departments in the areas concerned.

Indonesia AirAsia Flight QZ8501 pilot had asked the air traffic control on Sunday morning to deviate its flight path but disappeared shortly after. It was supposed to have landed in Singapore at 8.30am.

When contacted, a Meteorological Department spokesman confirmed that the Java Sea region had been experiencing thunderstorms and rain from 6am.

"There was no change in this (pattern) until noon, when it started to weaken," the spokesman said.

Universiti Teknologi Malaysia Associate Professor Salehuddin Muhammad said the QZ8501 pilot made the right call to avoid the storm by deviating from the flight path.

"A lot of things can happen to the aircraft (during a storm) - turbulence, bouncing in and out of weather."

He cited Air France 447, which crashed in 2009 killing all 228 on board after its equipment gave nonsensical readings due to obstruction from ice that formed while flying through a storm.

He said not all aircraft had the ability to climb out of storms, adding that small aircraft could ascend to certain heights and that it was up to pilots to see what to do next.

Malaysian Institute of Aviation Technology senior expert Ahmad Maulan Bardai said communication systems on aircraft such as the A320-200 was designed to work in bad weather.

"However, the weather situation may be beyond certain design characteristics," said Ahmad, declining to elaborate further.

He said bad weather alone could not account for QZ8501's disappearance, adding that more than one factor was usually present.