A preliminary federal report probing the cause of a crash of a Torrance-built Robinson Helicopter that killed two at the Port of Los Angeles earlier this month said a section of the craft’s main rotor blade was not recovered.

The brief five-paragraph narrative, released Friday by the National Transportation Safety Board, said all major components of the helicopter — except for the “outboard section of a main rotor blade” — were found in about 18 feet of water in the wake of the Jan. 4 crash.

“The fracture surface at the separation point was jagged and angular,” the report concluded.

Los Angeles-based attorney Ilyas Akbari of the firm Baum, Hedlund, Aristei and Goldman, which has handled several lawsuits against the company over fatal helicopter crashes, said those marks are consistent with several possible causes, including “mast-bumping.”

That’s the term used when a helicopter’s main rotor blade hits the main rotor drive shaft or “mast,” causing the chopper to crash with often fatal consequences.

“It is indicative of (the rotor blade) striking something,” Akbari said of the telltale marks. “If it is mast-bumping, we will know by the markings on the blade.”

Robinson helicopters have come under scrutiny by several aviation regulatory authorities for a series of crashes, many of them fatal.

In October, for instance, Robinson helicopters were placed on a New Zealand government watch list and several agencies stopped using them.

Last month, published reports said Australia had issued an air worthiness directive after the pilot of Robinson Helicopter reported unusual vibrations and landed. A crack in the rotor blade was later discovered.

The company has largely blamed the fatal crashes on pilot error rather than any design defects.

Company owner Kurt Robinson did not return a message left Friday seeking comment.

In the crash that occurred earlier this month, pilot Christopher Reed and photographer Michael Justice were killed when an R22 based at Torrance Municipal Airport plummeted into the harbor as the pair were taking pictures of cruise ships.

They were contracted by the Port of Los Angeles.

Justice was well-known by editors and photographers at the Daily Breeze, where he had long worked as a freelance photographer.

A celebration of life for Justice was held Friday at Ports O’ Call in San Pedro.

Akbari noted that while the R22 crash could have been caused by several different factors, including pilot error or maintenance issues, mast bumping was a possibility as well.

“Mast bumping is always a red flag when you see these things going down,” he said.