The National Transportation Safety Board says the engineer of the doomed Amtrak Train 188 apparently did not radio his dispatchers that his train had been hit by a projectile just before it careened off the tracks at the Frankford curve in Port Richmond.

A review of taped conversations by the engineer, Brandon Bostian, to dispatchers shows no mention of anything hitting his train, as one of his assistant conductors has reported.

NTSB's Robert Sumwalt, the lead investigator of the fatal derailment, said the Amtrak dispatchers were also interviewed about a possible report of a projectile impact.

"This idea of something striking the train – that's one of the many things we're looking at right now," Sumwalt told ABC This Week on Sunday.

"We interviewed the dispatchers and listened to the dispatch tape, and we heard no communication from the Amtrak engineer to the dispatch center to say that something had struck his train."

The NTSB has asked the FBI to examine the windshield of the Amtrak train, particularly an area about the "size of a grapefruit," with breakage that emanates out in a circular pattern.

Similar breakage is apparent on the windshield of the SEPTA train that did report being hit by something thrown or gunfire that night.

A third train, an Amtrak Acela, also reported being hit by something thrown around the same time Tuesday night.

An assistant Amtrak train conductor told the NTSB on Friday that she overheard a radio conversation between Train 188 engineer Brandon Bostian, 32, and the engineer of a SEPTA train, in which the SEPTA train reported being struck by something thrown or gunfire. That report has been substantiated by investigators.

The NTSB said she then heard Bostian say that his own train had also been struck by something. That is not heard on any tapes, however, the NTSB said Sunday.

Bostian, however, has said he suffered a concussion and has no recollection of anything after he passed the North Philadelphia train station, where he rang his bell as required.

Minutes later, his train accelerated to more than 100 m.p.h. - twice the posted speed limit on the Frankford curve - and the seven cars derailed, killing eight people and injuring more than 200 others.

Sumwalt made the rounds at various major networks' Sunday programs, discussing the projectile issue, the investigation and rail-safety improvements.

He told ABC the projectile possibility is "one of the things we're looking at." In addition to the train's accelerated speed, investigators will consider drug and alcohol analysis of Bostian and whether he might have used his cellphone while operating the train.

Bostian's lawyer has said the cellphone was put away and that Bostian had not taken drugs or alcohol.

Sumwalt called Sunday for the installation of inward-facing video cameras in trains. He said that would have helped the current investigation.

He and Amtrak CEO Joseph Boardman both reiterated Sunday the need for installation of state-of-the-art safety control system known as positive train control.

The Federal Railroad Administration on Saturday ordered Amtrak to immediately install current speed-control technology, known as automatic train control, at the Frankford curve and throughout the Northeast Corridor. Such a system is already in place on the southbound line at the curve.

If a train exceeds the speed limit, the system alerts the engineer to manually slow the train. If that doesn't happen in a few short seconds, the technology begins braking the train automatically.