A visual reconstruction of Washington plane crash

After a chilling night of search operations with at least six helicopters, officials believe all passengers and crew aboard the American Airlines jet and the US Army Black Hawk that collided midair and crashed into the Potomac River near Reagan Airport in Washington DC are dead.

The collision over the Potomac River occurred at 8.47 pm ET or 7.17 am Saturday IST on Wednesday, according to flight-tracking data. Using maps, videos, and live air traffic control transmissions, India Today's OSINT team piece together what occurred during the deadly, midair collision.

Sixty passengers and four crew members were aboard American Airlines Flight 5342, a Bombardier CRJ-700 operated by PSA Airlines, which departed from Wichita and was just minutes from landing at Reagan Airport.

Flying south over the Potomac River, a US Army helicopter with three crew members was on a night training flight. It was in contact with the air traffic control room but was not broadcasting ADS-B, the primary GPS-based aircraft tracking signal.

Its exact origin and takeoff time remain unknown, but its flight path was visible on a flight tracking site using MLAT (multilateration). This system calculates an aircraft's position by analysing Mode S signals, which is the secondary surveillance system.

As American Airlines flight 5342 approached the airport, it contacted air traffic control about landing on Runway 1. The controllers asked the pilots to use Runway 33 instead. The pilots confirmed the change and the aircraft was cleared to land.

Audio recordings from air traffic controllers captured dramatic exchanges before and after the collision. They include communications with other aircraft and the final attempt to contact the three Army crew members in the PAT25 helicopter before it crashed into the jet.

Also in contact with the air traffic control was the military helicopter, flying under the call sign PAT25. It confirmed American Airlines flight 5342 was in sight, which the helicopter pilot refers to as a "CRJ," based on the plane type CRJ-700. The air traffic control instructed the helicopter to pass behind the plane while the two aircraft were over 1.6 km apart. Here is an edited reproduction of the conversation between the air traffic control centre and the helicopter pilot:

Air Traffic Control: "PAT 25! Do you have the CRJ in sight?"

Air Traffic Control: "PAT 25, pass behind the CRJ."

Helicopter Pilot: "PAT 25 has aircraft in sight, request visual separation."

Here, "visual separation" requested by the helicopter crew means permission to continue flying while maintaining a safe distance from the passenger plane. The Air traffic control approved the request.

Less than 13 seconds later, an air traffic control transmission captured a shocked staff member saying "oh my" as the aircraft collided.

HELICOPTER WITHOUT ADS-B TO BLAME?

The passenger jet was broadcasting ADS-B data, which details an aircraft's position, including GPS-based latitude and longitude. However, the helicopter was not broadcasting ADS-B and was only broadcasting Mode S, a secondary surveillance and communication system.

Flight tracking platform Global ADSBexchange tracked the flight path of the helicopter using multilateration (MLAT).

MLAT is a flight tracking technique that determines aircraft position by measuring the time difference of arrival (TDOA) of signals sent from the aircraft to multiple ground stations.

The Black Hawk may not have been equipped with ADS-B at all - however, it did have a transponder and would have been visible on air traffic control radar.

The jet was likely equipped with the Traffic Alert and Collision Avoidance System (TCAS), which, at a higher altitude, would have likely prevented this collision. However, experts suggest it was likely deactivated near the runway at a lower altitude to avoid nuisance/false alerts from ground traffic during taxiing operations.

While an investigation is still underway, the congestion at the Reagan Airspace, which is one of the busiest runways in the United States, is to be factored in. The Federal Aviation Administration has reportedly warned, including in June last year, that a shortage of air traffic controllers along the eastern seaboard has forced it to restrict the number of flights it can permit through the area.