An essential safety feature was deactivated on the US Army helicopter that crashed into an American Airlines regional jet close to Reagan Airport in Washington last week, claiming the lives of 67 people.

Senate Commerce Committee chair Ted Cruz told reporters the Black Hawk helicopter had turned off its automatic dependent surveillance-broadcast (ADS-B), which is permitted for military aircraft.

“This was a training mission, so there was no compelling national security reason for ADS-B to be turned off,” Cruz said after a briefing from the National Transportation Safety Board and Federal Aviation Administration.

In the deadliest US air disaster in more than 20 years, the aircraft collided last week, with both aircraft plunging into the Potomac River.

The helicopter was flying about 100 feet over the maximum allowed for that route, the NTSB said earlier.

ADS-B is an advanced surveillance technology to track aircraft locations.

Cruz noted the helicopter had a transponder so it would appear on radar but ADS-B is significantly more accurate.

Last week, Senator Maria Cantwell, the top Democrat on the committee, questioned why the FAA since 2018 has allowed military flights to fly with their installed ADS-B equipment off.

The FAA also said on Thursday it has begun reviewing airports with high volumes of mixed helicopter and airplane traffic nearby after Cruz said he had sought a safety review.

In the aftermath of the crash, the FAA has imposed significant restrictions on helicopter flights around Reagan National until at least late February and two of the lesser-used runways remain closed.

When police, medical or presidential transportation helicopters must use the airspace, civilian planes are not allowed to be in the same area, according to an FAA advisory.

NTSB Chair Jennifer Homendy told reporters it appears based on the cockpit voice recorder that the helicopter pilot was wearing night vision goggles.

She also said the helicopter had been recovered from the Potomac River and it would likely be several days before the NTSB can confirm that the helicopter’s ADS-B was off during the crash.

US Transportation Secretary Sean Duffy also questioned some military training and other missions.

“We’re going to hopefully find this out, but if they had night vision goggles on a mission like that at nine o’clock at night and not at 1 a.m. – it is unacceptable,” Duffy said on Wednesday.