RENO -- Federal investigators said Wednesday they're perplexed by the jet engine fire that preceded the fatal crash of an air tanker near Reno this week because there's been no known similar incident before in that type of aircraft.

They also say the Lockheed P2V-7 that crashed shortly after take off Monday evening from Reno-Stead Airport had been inspected not long ago and was only about 36 hours through a normal 100-hour inspection schedule.

``What precipitated the fire, we don't know,'' said Tom Little, lead investigator for the National Transportation Safety Board.

``I asked the operator if they had ever experienced anything like this and they haven't,'' he said.

The plane owned by Neptune Aviation Services of Missoula, Mont., and built in 1962 was one of 12 the company had on contract with the Forest Service to fight fires.

Lockheed started building the planes for the U.S. military in the mid-1940s -- ``the predecessor of the P-3, the submarine chasers,'' Little said. ``This was one of the later models.''

Typically powered by propellers, the plane that crashed had been retrofitted with two additional jet engines for added thrust during take off, Little said.

It was one of the jet engines that at least two witnesses saw on fire shortly after take off. The flames engulfed the left wing before the plane went into a roll and crashed, killing all three members of the aerial firefighting crew, he said.

The names of the victims have not been released. Little said those identities eventually would come from the Washoe County Medical Examiners Office, but officials for that office said they had no information to release as of Wednesday afternoon.

Little planned another news briefing at the Reno-Stead Airport at 6 p.m. Wednesday.

Little told reporters on Tuesday that investigators had recovered several large pieces of metal beginning about one-quarter mile north of the runway that appear to have come from the burning engine.

``It appears it had disintegrated and subsequently left the aircraft,'' he said.

Little said they found nothing on the runway or surrounding area that would explain why the engine caught fire. He said he talked with officials for Neptune who helped survey the crash site on Tuesday, including one veteran pilot.

``He'd flown this kind of plane for almost 30 years and never seen this before. He said he'd never seen an anomaly of this type,'' Little said.

``There will be more research on our part to see if we find anything that might be associated with this, but right now we have an anomaly,'' he said.

``We have a fire. We have evidence that is factual in nature that the jet engine came apart. How that played in the loss of control, we don't know yet,'' he said.

``We have no communication from the pilot or co-pilot relative to an anomaly with the aircraft,'' he added.

Monday's crash marked at least the third time a P2V owned by Neptune suffered a fatal crash while fighting wildfires on government contract over the past 15 years. Two men were killed when one crashed near Missoula in 1994 and two other men died in a crash near Reserve, N.M., in 1998.

Neptune Aviation Chief Executive Officer Mark Timmons said those previous crashes were found to be caused by pilot error.