MOSCOW (AP) - Russia's aviation authority has suspended flights aboard Boeing 737s until the nation's pilots receive additional training after a recent deadly crash, an official said Thursday.

All 88 people aboard a Boeing 737-500 died when the plane operated by the Russian Aeroflot-Nord crashed Sept. 14 while preparing to land in the Ural Mountains city of Perm.

Federal Agency of Air Transport spokesman Sergei Samoshin said the agency has suspended flights by planes similar to the one that crashed until pilots can undergo more training on simulators.

Samoshin said that Russian carriers now operate 107 Boeing 737s. He wouldn't say how many of them will be affected by the measure or specify how long the suspension would last.

RIA Novosti news agency said the measure referred to a sub-type of Boeing 737-500 which is in service with six Russian carriers. It didn't say how many planes will be affected.

The training was necessary to make sure that all pilots properly read a key indicator showing the plane's attitude, the so-called attitude indicator or artifical horizon, Samoshin said.

The attitude indicator, which informs the pilot about the plane's orientation in relation to the ground, is designed differently on Soviet-made planes and Western airliners.

Transport officials initially blamed the crash in Perm on a faulty engine that caught fire, but the investigating committee said it had found no sign of engine fire or other malfunction.

Investigators have yet to determine what caused Russia's worst air disaster in two years. Aviation experts and observers said the crash was likely caused by a pilot error.

Perm flight controller Irek Bikbov said in remarks broadcast by state-run Channel One television on the day of the crash that the plane's pilot was behaving strangely, disobeying orders to descend on the final approach and instead taking the jet to a higher altitude. Bikbov said he then ordered the pilot to make a second run, but instead of making the right turn he turned left. When the controller asked the pilot if things were normal on board, the pilot answered positively.

Some experts say the pilot's strange behavior could have been caused by his failure to properly read the attitude indicator's reading which could have led to a dangerous maneuver and then crash. The pilot of the plane which crashed in Perm had flown Soviet-made planes before and had relatively little experience in piloting Boeing planes.