The Army goggles would have made it difficult to see the plane’s colored lights, which might have helped the Black Hawk determine the plane’s direction. The goggles also limited the pilots’ peripheral vision as they flew near Ronald Reagan Washington National Airport.

The challenges posed by night-vision goggles were among the topics discussed at the NTSB’s third and final day of public testimony over the fatal midair crash, which killed all 67 people aboard both aircrafts.

Experts said another challenge that evening was distinguishing the plane from lights on the ground while the two aircraft were on a collision course. Plus, the helicopter pilots may not have known where to look for a plane that was landing on a secondary runway that most planes didn’t use.

“Knowing where to look. That’s key,” said Stephen Casner, an expert in human factors who used to work at NASA.

Two previous days of testimony underscored a number of factors that likely contributed to the collision, sparking Board Chairwoman Jennifer Homendy to urge the Federal Aviation Administration to “do better” as she pointed to warnings the agency had ignored years earlier.

Some of the major issues that have emerged so far include the Black Hawk helicopter flying above prescribed levels near the airport as well as the warnings to FAA officials for years about the hazards related to the heavy chopper traffic there.

It’s too early for the board to identify what exactly caused the crash. A final report from the board won’t come until next year.

But it became clear this week how small a margin of error there was for helicopters flying the route the Black Hawk took the night of the nation’s deadliest plane crash since November 2001.

Army Colonel Andrew DeForest told the NTSB that “flights along the D.C. helicopter routes were considered relatively safe,” but some pilots in the 12th Battalion that flew alongside the crew that crashed told investigators they regularly talked about the possibility of a collision because of the congested and complicated airspace.

The American Airlines jet arrived from Wichita, Kansas, carrying, among others, a group of elite young figure skaters, their parents and coaches, and four union steamfitters from the Washington area.

The collision 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.

‘Significant frustration’

NTSB members scolded FAA officials during Friday’s hearing, accusing them of saying the right things about safety in public while failing to cooperate in private. They said the FAA has repeatedly refused to provide information requested by investigators.

Board member Todd Inman said there was “significant frustration between what’s actually occurring” and “what’s being said for public consumption.”

Frank McIntosh, the head of the FAA’s air traffic control organization, said he would start working immediately to make sure the agency complies with the investigation. McIntosh also acknowledged problems with the culture in the tower at Reagan National, despite past efforts to improve compliance with safety standards.

“I think there were some things that we missed, to be quite honest with you, not intentionally, but I was talking about how certain facilities can drift,” McIntosh said.

Homendy told McIntosh she believes agency leaders are sincere about wanting to improve safety, but the solution must be more than just sending a top-down message of safety and also actually listening to controllers in the field.

Questions over lack of alcohol testing

Tim Lilley, an aviation expert whose son Sam was a pilot on the passenger jet, said he’s optimistic the tragic accident will ultimately lead to some positive changes.

“But we’ve got a long way to go,” he told The Associated Press.

Lilley said he was particularly struck by the FAA’s lack of alcohol testing for air traffic controllers after the crash.

“And they made a bunch of excuses why they didn’t do it,” Lilley said. “None of them were valid. It goes back to a whole system that was complacent and was normalizing deviation.”

Homendy said during Thursday’s hearings that alcohol testing is most effective within two hours of a crash and can be administered within eight hours.

Nick Fuller, the FAA’s acting deputy chief operating officer of operations, testified that the controllers weren’t tested because the agency did not immediately believe the crash was fatal. The FAA then decided to forgo it because the optimum two-hour window had passed.

Controller didn’t warn the jet

FAA officials testified this week that an air traffic controller should have warned the passenger jet of the Army helicopter’s presence.

The controller had asked the Black Hawk pilots to confirm they had the airplane in sight because an alarm sounded in the tower about their proximity. The controller could see from a window that the helicopter was too close, but the controller did not alert the jetliner.

In a transcript released this week, the unidentified controller said in a post-crash interview they weren’t sure that would have changed the outcome.

Additionally, the pilots of the helicopter did not fully hear the controller’s instructions before the collision. When the controller told the helicopter’s pilots to “pass behind” the jet, the crew didn’t hear it because the Black Hawk’s microphone key was pressed at that moment.

‘Layer after layer of deficiencies’

Jeff Guzzetti, a former NTSB and FAA crash investigator, told the AP that a combination of factors produced this tragedy, like “holes that line up in the Swiss cheese.”

Any number of things, had they been different, could have prevented the collision, he said. They include the Black Hawks having more accurate altimeters, as well as a key piece of locating equipment, known as ADS-B Out, turned on or working. In turn, air traffic control could have seen the problem earlier.

Just a few feet could have made a difference, Guzzetti said.

“It just goes to show you that an accident isn’t caused by one single thing,” Guzzetti said. “It isn’t caused by ‘pilot error’ or ’controller staffing.’ This accident was caused by layer after layer of deficiencies that piled up at just the right moment.”

Ex-official: FAA and Army share blame

Mary Schiavo, a former U.S. Department of Transportation Inspector General, told the AP that both the Army and the FAA appear to share significant blame.

The Black Hawks’ altimeters could be off by as much as 100 feet and were still considered acceptable, she said. The crew was flying an outdated model that struggled to maintain altitude, while the helicopter pilots’ flying was “loose” and under “loose” supervision.

“It’s on the individuals, God rest their souls, but it’s also on the military,” Schiavo said. “I mean, they just seem to have no urgency of anything.”

Schiavo was also struck by the air traffic controllers’ lack of maps of the military helicopter routes on their display screens, which forced them to look out the window.

“And so everything about the military helicopter operation was not up to the standards of commercial aviation … it’s a shocking lack of attention to precision all the way around,” she said.

Schiavo also faulted the FAA for not coming off as terribly responsive to problems.

“I called the Federal Aviation Administration, the Tombstone Agency, because they would only make change after people die,” Schiavo said. “And sadly, 30 years later, that seems to still be the case.”