What Black Hawk's radio traffic reveals before one of deadliest mid-air collisions in US history
Investigations into what caused the mid-air collision between an American Airlines jet and a US Army Black Hawk helicopter are ongoing and the radio communications will be crucial in determining the cause.
Moments before the collision, ATC, or air traffic control, can be heard on their radio directing multiple planes taking off and landing at Ronald Reagan Washington National Airport.
When the Black Hawk helicopter, with the callsign PAT 25, approached the airspace shared with other commercial flights taking off and landing, the pilot requested how they wanted to be "controlled" in the airspace and was ultimately approved by the ATC tower.
ATC audio traffic before and after the crash released by LiveATC.net reveals the final moments of communication between ATC and the Black Hawk, and it contains some key details aircraft crash investigators will now be looking into.
Minutes before the crash, the pilot flying the Black Hawk checks in on the radio frequency with simply saying "PAT 25 Memorial," and the air traffic controller in the tower acknowledges with "PAT 25 roger".
Moments later, ATC then warns the military pilot about an inbound aircraft preparing to land: "Traffic [American Airlines passenger plane] just south of the Woodrow Bridge, a CRJ, it's 1,200 feet setting up for Runway 33."
The Black Hawk pilot responds with: "PAT 25 has the traffic in sight, request visual separation."
The air traffic controller immediately responds with "visual separation approved" and this will be key in the investigation.
Visual separation, sometimes known as "see and avoid", is regularly used to deconflict airspace and pilots use this method to stay well clear of any known dangers they can physically see out of their windows, such as other aircraft, communications towers and pylons.
According to flight radar taken at the time, after the being approved, the Black Hawk and passenger plane continue on the same path.
Moments later the two aircraft get even closer, and ATC checks back in with the Black Hawk helicopter and asks the pilot: "PAT 25 do you have the CRJ in sight?" followed immediately by saying "PAT 25 pass behind CRJ".
The black hawk pilot responds: "PAT 25 has aircraft in sight request visual separation".
The air traffic controller responds and acknowledges only with "visual separation".
Around 20 seconds later another radio user is heard saying something inaudible and a few seconds later another person appears on the radio to say "Did you see that?"
Radar shows both aircraft continued on the same flight path and ultimately made contact, causing one of the deadliest mid-air collisions in US history.
Upon realising what has happened, aircraft controllers immediately, in a calm manner, begin to clear the airspace and start re-routing aircraft to "go around" and requesting some aircraft to "immediate land" and others told to "return to base".
Another aircraft going by the callsign of "Blackjack" was asked if they could help with search and rescue efforts and if they had a searchlight on board.
Investigators will want to understand why the pilot requested "visual separation" in such a heavily congested and busy airspace at night and why it was approved.
Because of the time of day, the Black Hawk crew would have been flying wearing night vision goggles which can sometimes restrict peripheral vision and can also alter the wearer's depth perception.
So what other deconfliction and airspace control measures do ATC and pilots use?
Vertical separation
Both aircraft will typically be required to use their aircraft's altimeter and work with the same pressure setting, which is important when it comes to the accuracy of their aircraft's altitude or flight level readings.
Pilots will usually be informed by ATC which altitude or flight level they must adhere to. For example, two pilots in the same airspace could be told by air traffic control... "Aircraft 1, remain above 10,000 feet"... "Aircraft 2, you have ground up to 8,000 feet – you're to remain below this maximum altitude".
Even with human error or minor inaccurate readings, it would comfortably see a 2,000ft vertical separation or buffer for both aircraft to fly blind, essentially, if both aircraft remained within those parameters, and there would be no real risk of collision.
Lateral separation
Lateral separation can be achieved by various means, including the use of highly visible geographical features and landmarks, or known points and datum on a map, radar etc.
This, for example, could be: "Aircraft 1, you are to remain 1 kilometre south of the River Thames at all times" and "Aircraft 2, you are to remain 1 kilometre north of the River Thames at all times".
In this instance, it would rely on both pilots checking their on-board instruments and out of their windows to see their current location and remain within those parameters.
A combination of other deconfliction measures can be used at any time and the situation and pre-planned or predefined procedures dictate what should be used and when.
A NOTAM is a Notice to Aviation, sometimes known as a Notice to Airmen or Notice to Air Missions, and is a constantly updated notice filed with an aviation authority to alert all aircrew of any potential hazards along a flight route.
It is the responsibility of all air users to read and familiarise themselves with the up-to-date notices prior to flight.
Join Our Newsletter
