Investigators have said the crew of the Tu-204 plane that made a belly landing in the woods on its approach to a Moscow airport earlier this week used a pocket GPS instead of the primary air navigation system, a leading Russian business daily said on Thursday.

The plane, with only eight crew members onboard, made an emergency landing near Moscow's Domodedovo Airport on Monday, while returning from Egypt. The plane carries around 200 passengers.

The Interstate Aviation Committee (IAC), which is investigating the incident, was quoted by Kommersant as saying in a statement that Domodedovo International Airport was equipped with a special navigation system which allows a pilot to land a plane even in the most difficult weather conditions.

However, an IAC official told the paper that data from the plane's flight recorder showed the crew switched off the system while landing the aircraft and used a pocket GPS instead. Investigators are yet to reveal what forced the crew to take such a decision. So far, the onboard navigation system failure is believed to be the possible explanation for the plane crash.

Experts were quoted by Kommersant as saying pilots have the right to switch from the air navigation system to a manual guidance system if the main system fails. But it is possible to land a plane using manual guidance only in ideal visibility. The weather in Moscow was cloudy with heavy fog on Monday when the crash occurred.

If the crew makes the decision to switch to manual guidance, they are obliged to notify an air traffic control of that decision, experts told the paper. The crew of the Tu-204 plane, however, failed to do this.

Alexander Potapov, the flight director of the Aviastar-Tu air company, which operates the plane, ruled out a possible air navigation system failure, and defined as "nonsense" the investigators' suggestion that the plane's crew used a pocket GPS to land the plane.

"I know that some pilots carry GPS navigators with them on a plane, but we do not welcome this, they should work with standard equipment," he said.

Chief Tu-204 test engineer of the Aviastar-Tu company Oleg Ganovich was quoted by the paper as saying pilots of small planes sometimes use portable GPS navigators during flights. However, he said, it is "senseless" to use them on board a Tu-204 plane as the plane has other equipment in case of an emergency landing.