Human error or congestion? What caused the American Airlines plane crash in Washington?

“This was a dark and excruciating night in our nation’s capital and in our nation’s history, and a tragedy of terrible proportions. As one nation, we grieve for every precious soul that has been taken from us so suddenly.”

United States President Donald Trump expressed grief on Thursday morning as he addressed the nation and the world on the mid-air collision that took place between an American Airlines flight and a US Army helicopter, which sent both aircraft into the Potomac River below, presumably killing all 67 people — 64 on board the plane and three on the Black Hawk helicopter.

As people mourn this horrible tragedy — this is the deadliest US air disaster since November 2001 — many are still struggling to understand how a deadly mid-air collision could occur in what experts describe as “the most controlled bit of airspace in the world”.

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Collision between American Airlines flight and Black Hawk

American Airlines Flight 5342 from Kansas collided with a US Army Black Hawk helicopter near Ronald Reagan National Airport at 8:47 pm, local time, Wednesday. The crash, according to National Transportation Safety Board member J Todd Inman, appeared to have been a “very quick, rapid impact”.

Eyewitnesses who saw the tragedy taking place were aghast at what they witnessed. “It (the explosion) looked to me like a giant Roman candle, sparks shooting from the head of the plane down to the tail. I saw that for about two seconds,” said Ari Schulman to NBC Washington.

Video from an observation camera at the nearby Kennedy Centre shows the collision.

Audio sourced from LiveATC.net, which provides live air traffic control broadcasts from air traffic control towers and radar facilities around the world, reveals the plane had initially been cleared to land on runway 1. But an air traffic controller asked the flight crew if they could use runway 33 instead.

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Then less than 30 seconds before the collision, an air traffic controller at Reagan National Airport issued a call to the military helicopter: “PAT25, do you have the CRJ in sight?” Moments later, another directive was given: “PAT 25 pass behind the CRJ.”

There was no response from the helicopter. Seconds later, the two aircraft collided. A pilot observing the incident made an urgent call over the radio: “Tower, did you see that?”

Following the crash, one could hear one of the air traffic controllers saying, as per a Reuters report, “Crash, crash, crash, this is an alert three.”

Following the crash and both aircraft plunging into the Potomac, around 300 responders reached the spot for search-and-rescue officials. However, no survivors have been found with officials being able to recover 40 bodies from the waters.

Additionally, the plane’s black boxes have been recovered from the water, which could offer clues about the cause of the crash.

Human error and miscommunications

As investigations into the collision have begun, with US President Donald Trump promising a thorough probe to determine just what went wrong, many experts are wondering if human error is to blame for the tragedy in the skies.

Many aviation experts suggest that the pilots of the American Airlines flight as well as the Black Hawk failed to perform the time-honoured method of “seeing and avoiding”, which could have been the reason for the collision.

The pilots of the military UH-60 Black Hawk helicopter did confirm to controllers that they had visually identified the American Airlines jet as they crossed its path and were avoiding it. They may have identified the wrong approaching airliner, initial speculation suggests.

As Juan Browne, an American airline pilot with an influential aviation channel, told the New York Times: “For whatever reason the helicopter did not see and avoid the CRJ (the American Airlines plane) as he was directed to do by the air traffic controller and ran straight into it. The CRJ was on a stable approach exactly where it was supposed to be and doing what it was supposed to be doing.”

Philip Greenspun, an MIT professor and former Delta pilot, was also of the opinion that the mid-air collision was most likely the result of human error stemming from a confluence of factors. In The Independent, he notes that the chief possibility could have been a misunderstanding between air traffic controllers and the Black Hawk pilots.

Some also note that miscommunication from the Air Traffic Control could have been the cause of the crash. As Jeff Guzzetti, a former accident investigator for the Federal Aviation Administration (FAA) and the National Transportation Safety Board (NTSB), told NBC News any dialogue with air traffic control will be a primary focus of the investigation.

For instance, the controller at Reagan National Airport is heard telling the helicopter pilot if he saw the ‘CRJ’ — the type of airplane — in the sky, without indicating where it was. Retired Black Hawk pilot Lt Col Darin Gaub said that this doesn’t align with the language normally used. “The language is usually more along the lines of … ‘Black Hawk, hey, do you see the aircraft at your 11 o’clock, five miles out, moving north?’ or something along those lines,” he was quoted as telling the New York Post.

Bright lights and congestion at Reagan Airport

Some experts note that the congestion in the skies above the Reagan National Airport could have been one of the contributing factors to the mid-air collision.

Located along the Potomac just southwest of Washington, Reagan Airport is much closer to the city than the larger Dulles International Airport in a congested and complex airspace that requires pilots to navigate among hundreds of commercial planes, military aircraft, and around restricted areas that include sensitive sites.

Ross Aimer, a retired United Airlines captain and chief executive officer of Aero Consulting Experts, told the Associated Press, “This was a disaster waiting to happen. Those of us who have been around a long time have been yelling into a vacuum that something like this would happen because our systems are stretched to extremes.”

Some also note that the congestion in the skies could have led to a saturation of lights, causing the tragedy.

Aviation experts said there is also a possibility that the aircraft were in each other’s blind spots — which planes and helicopters have, just like cars. The fact that the two aircraft were so close to the ground would have meant they had limited time to manoeuvre around blind spots. “Helicopter pilots can’t be just constantly leaning forward or backward, because you could become disoriented,” Shawn Pruchnicki, a former airline pilot and an assistant professor at the Centre for Aviation Studies at Ohio State University, explained to NBC News. “So there could have been a visual obstruction for them as they were trying to find this jet, and they ran out of time.”

There are also questions being raised about the TCAS — traffic collision avoidance system. While all commercial aircraft in the US are fitted with this warning system, their sensitivity is adjusted as the aircraft approaches its landing. Some of its alert functions are inhibited because instructions to descend near the ground would be dangerous and to avoid distracting pilots.

Some even speculate that the helicopter pilot’s night vision goggles may have contributed to the accident. Helmets, just as goggles, significantly reduce peripheral vision, which can also make it harder to see brightly-lit objects against dark backgrounds, like an airliner in a dark sky with its landing lights blazing. “Night vision takes your normal field of vision from what you see normally to down to about a 40-degree angle, and that affects each pilot in the front, Gaub said in a New York Post report.

What comes next

The NTSB and the FAA have begun investigating the collision and the eventual collapse into the Potomac River. While authorities haven’t given any clear reason as to what happened, US President Donald Trump said that federal diversity efforts could have been a factor, without providing any evidence.

As of now, investigators have recovered the cockpit voice recorder and flight data recorder from the aircraft and they are now at the NTSB’s labs for evaluation. Board member Todd Inman said officials aimed to release a preliminary report into the incident within 30 days. “We will take the time that’s necessary,” he said. “If we find something that is a significant issue that warrants immediate action, we will not hesitate to make those recommendations and make them public.”

With inputs from agencies