Do flight paths cross? Your Washington DC plane crash question answers

On Wednesday night a passenger jet collided with a helicopter in Washington DC with all passengers and crew on both aircraft feared dead — but how did it happen?

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Earlier this week, American Airlines flight 5342 was approaching Ronald Reagan National Airport when it collided in mid-air with an Army Black Hawk helicopter, with all 67 people on board both aircraft feared dead.

The passenger jet was en route from Wichita, Kansas, to Washington DC when it was involved in a collision. The flight was operated by PSA Airlines with a CRJ-700. In total, there were 60 passengers onboard the flight, and four crew members. As of Thursday evening, at least 40 bodies have been recovered, a law enforcement source told CBS News.

As many as 15 of the 64 passengers and crew on board the flight are believed to have been involved with figure skating. As investigations into the collision commence, there are many questions to be answered by officials. We have also tried to answer some aviation questions you may have in the wake of the tragedy.

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Do flight paths cross?

Whilst flight paths usually do cross, this is normally at different altitudes. Different aircraft flying on intersecting paths will usually be assigned different altitudes to ensure separation and avoid mid-air collisions.

Each plane, for example, will have a specific 'flight level' based on their flight plan and airspace regulations.

Does this change when an aircraft is landing?

When an aircraft is due to land, its altitude significantly decreases as it approaches the runway. This means the aircraft is usually at a much lower level in the air. This process will be managed by air traffic control to ensure there is safe separation between planes at different stages at flight.

In regards to the crash in Washington DC, the permitted flight ceiling on the Potomac River near Reagan National Airport is 200 feet. This ensures that the heavy flow of military helicopters in the area stays safely clear of the steady stream of commercial aircraft traffic heading into and out of Reagan National Airport.

So why were American Airlines flight 5342 and the Black Hawk helicopter at the same altitude?

According to CBS News, data collated from FlightRadar24, revealed that the helicopter's last estimated altitude was about 400 feet when it crashed and the passenger jet's altitude was about 375 to 400 feet, according to data from FlightAware and FlightRadar24. According to this data, the Black Hawk helicopter was 200 feet above the flight ceiling.

How common are mid-air collisions?

Mid-air collisions are extremely rare. On average, there has been one per year so far this century and most of these involved small private aircraft and/or helicopters, according to The Independent.

Both pilots and air traffic controllers are focused on avoiding incidents in the sky. Larger passenger aircraft are also equipped with a traffic collision avoidance system, which is known as TCAS. If a potential collision is identified, then the system will issue a 'resolution advisory' and typically one aircraft will instructed to climb, whilst the other is told to descend.

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Pilots are required to perform the maneuver specified by the resolution advisory, even if it conflicts with instructions from air traffic controllers. The Washington tragedy, however, involved a helicopter, which makes the situation slightly different. Helicopters have very different operational characteristics. In this case, it is also not known if the Black Hawk helicopter was fitted with TCAS.

However, in any case, the system becomes inhibited when the aircraft is very close to the ground.

What will the investigation look like?

Like any type of investigation, the inquiry into the Washington DC crash will entail several stages. Investigators will gather evidence from the crash site on the Potonac River, analyse data from each aircraft's flight recorders known as black boxes, interview witnesses, examine wreckage and piece together the sequence of events that lead up to the collision.

Collating the evidence ultimately aims to determine the cause of the incident, and issue safety recommendations to prevent future occurrences. At the moment, the investigation into the Washington DC tragedy is in the initial stages, where a recovery operation is still underway. Whilst it is unclear how long this investigation will take, they usually last between one and two years.

What flights land at Reagan National Airport?

Reagan National Airport opened in 1941 and is very close to the centre of Washington. During normal operations, the airport handles up to 60 flights per hour which can be nonstop flights to 101 domestic and 5 international destinations. It is a hub for American Airlines and has two terminals.

Most international flights to the US capital, arrive at Dulles airport which is around 20 miles west of the city centre.