Aviation Expert Makes Key Observation As Cause Of Deadly American Airlines Crash Remains Unknown

A key safety feature to avoid mid-air collisions involving commercial aircraft was probably not being used on an American Airlines passenger jet that collided with an Army Black Hawk above the Potomac River Wednesday evening and that may have been by design.

Commercial aircraft are equipped with a traffic alert and collision avoidance system known as TCAS. The system monitors airspace around an aircraft for other aircraft equipped with a corresponding active transponder.

Retired former NTSB Managing Director Peter Goelz says the system probably was not active on the aircraft at the time of the crash.

"That system essentially shuts down at 1,000 feet," Goelz said on CNN Thursday morning. "So TCAS was probably not in play last night."

He says as planes approach landing, the responsibility falls on air traffic controllers and pilots.

"People in the cockpit, the flight crew, see and avoid and rely on the controller," Goelz added.

60 passengers and four crew members were on the American Airlines flight and three U.S. Army personnel were on the Black Hawk helicopter.

Officials said on Thursday morning that there were no survivors.

At a news conference, American Airlines CEO said that the Army helicopter veered into the plane's landing path but investigators are still looking into the cause of the crash.

"Was the Black Hawk under any control or monitoring?" Goelz asked.