Investigators probing the January midair collision of a passenger plane and an Army helicopter over Washington that killed 67 people found the chopper was flying higher than it should have been and the altitude readings were inaccurate.

The details came out of the first day of National Transportation Safety Board hearings in Washington, where investigators aim to uncover insights into what caused the crash between the American Airlines plane from Wichita, Kansas, and the Black Hawk helicopter over Ronald Reagan National Airport.

The board opened the three days of hearings by showing an animation and playing audio and video from the night of the collision, as well as questioning witnesses and investigators about how the Federal Aviation Administration and the Army may have contributed to nation’s deadliest plane crash since November 2001.

It’s likely too early for the board to identify what caused the crash.

The January incident was the first in a string of crashes and near misses this year that have alarmed officials and the traveling public, despite statistics that still show flying remains the safest form of transportation.

Animation, altimeter discrepancy

The hearing opened Wednesday with a video animation showing where the helicopter and airliner were leading up to the collision. It showed how the helicopter flew above the 200 feet (61 meters) altitude limit on the helicopter route along the Potomac River before colliding with the plane.

Investigators said Wednesday the flight data recorder showed the helicopter was actually 80 feet to 100 feet (24 to 30 meters) higher than the barometric altimeter the pilots relied upon showed they were flying. So the NTSB conducted tests on three other helicopters from the same unit in a flight over the same area and found similar discrepancies in their altimeters.

Dan Cooper with Sikorsky helicopters said that when the Black Hawk helicopter involved in the crash was designed in the 1970s, it used a style of altimeter that was common at the time. Newer helicopters have air data computers that didn’t exist back then that help provide more accurate altitude readings.

Chief Warrant Officer Kylene Lewis told the board that she wouldn’t find an 80 to 100 foot discrepancy between the different altimeters on a helicopter alarming because at lower altitudes she would be relying more on the radar altimeter than the barometric altimeter. Below 500 feet (152 meters), Lewis said she would be checking both instruments and cross referencing them.

DC helicopter route permanently closed after fatal Black Hawk crash

She said as long as an altimeter registers an altitude within 70 feet of the published altitude before takeoff the altimeter is considered accurate under the checklists.

Army officials said a discrepancy of 70 to 100 feet (21 to 30 meters) between the Black Hawk’s altimeters is within the acceptable range because pilots are expected to maintain their altitude plus or minus 100 feet.

The greater concern is that the FAA approved routes around Reagan airport that included such small separation distances between helicopters and planes when planes are landing.

“The fact that we have less than 500 foot separation is a concern for me,” the Army’s Scott Rosengren said.

But Rosengren said that “if he was king for a day” he would immediately retire all the older Black Hawk models like the one involved in this crash and replace them with newer versions of the helicopters.

Previously, NTSB Chairwoman Jennifer Homendy highlighted that the published helicopter routes around Washington D.C. would allow planes and helicopters to routinely come within 75 feet of each other during landing.

Army officials said Wednesday that the flight manual for these older Black Hawks doesn’t highlight the discrepancies in altimeters that has been documented previously, but typical flight separations are at least 500 feet (152 meters) around airports.

Previously disclosed air traffic control audio had the helicopter pilot telling the controller twice that they saw the airplane and would avoid it. The animation ended with surveillance video showing the helicopter colliding with the plane in a fiery crash.

Investigations have already shown the FAA failed to recognize a troubling history of 85 near misses around Reagan airport in the years before the collision, and that the Army’s helicopters routinely flew around the nation’s capitol with a key piece of locating equipment, known as ADS-B Out, turned off.

Aviation attorney Bob Clifford, who is working to file one of the first lawsuits against the government next month, said he hopes NTSB will look beyond the immediate factors that caused this crash to highlight the bigger ongoing concerns in the crowded Washington airspace.

Proposed changes

Even though the final NTSB report won’t be released until sometime next year, U.S. Sen. Ted Cruz introduced legislation Tuesday to require all aircraft operators to use both forms of ADS-B, or Automatic Dependent Surveillance Broadcast, the technology to broadcast aircraft location data to other planes and air traffic controllers. Most aircraft today are equipped with ADS-B Out equipment but the airlines would have to add the more comprehensive ADS-B In technology to their planes.

“There cannot be a double standard in aviation safety,” Cruz said. “We should not tolerate special exceptions for military training flights, operating in congested air space.”

The legislation would revoke an exemption on ADS-B transmission requests for Department of Defense aircrafts. It also would require the FAA to evaluate helicopter routes near airports and require the Army Inspector General to review the Army’s aviation safety practices.

Homendy said her agency has been recommending that move for decades after several other crashes.

Transportation Secretary Sean Duffy said that while he’d like to discuss “a few tweaks,” the legislation is “the right approach.” He also suggested that the previous administration “was asleep at the wheel” amid dozens of near-misses in the airspace around Washington’s airspace.

‘Fact-finding proceeding’

Homendy said the hearings over the next few days will be a “fact-finding proceeding.” The NTSB will also post thousands of pages of evidence from the crash investigation online.

FAA Administrator Bryan Bedford said that he expects “we’re going to have some very uncomfortable conversations over the next two and a half days” but that “they need to be had in the clear light of day – and simply put the best interest of the traveling public ahead of any of our personal interests, perhaps.”

The hearings in Washington involve NTSB board members, investigators and witnesses for organizations involved in the crash.

Federal officials have also raised concerns over the nation’s outdated and understaffed air traffic control system. During January’s mid-air crash above Washington, one controller was handing both commercial airline and helicopter traffic at the busy airport.

Associated Press writers Leah Askarinam, Ben Finley and Rio Yamat contributed to this story.