MOSCOW, March 13 (RIA Novosti) - Many of the Russian MiG-29 Fulcrum fighter planes grounded after last December's crash have shown signs of metal corrosion, a military official said on Friday.

Since the MiG-29 crash in East Siberia last December, in which the pilot died, a Defense Ministry commission has inspected around 200 aircraft, clearing more than 100 for further flights, but finding about 90 to be defective.

Lt. Gen. Sergei Bainetov, head of flight security at the Russian Air Force, said that even new aircraft which had clocked no more than 150 flight hours showed signs of metal corrosion in their tail sections.

Experts are looking into the possible causes of the corrosion.

The December crash was the second in East Siberia involving a MiG-29 fighter in less than two months. In mid-October, a MiG-29 crashed 60 kilometers (37 miles) from the Domna airfield in the Chita Region during a training flight. The pilot ejected safely.

Last year, two Russian Air Force MiG-29 fighters were involved in a mid-air collision over the Rostov Region. Both pilots ejected safely.