Further insights into the January 2025 Washington DC accident

After the accident, it was immediately clear that helicopter traffic operating on Helicopter Route 4 posed a risk of a midair collision with aircraft landing on runway 33 at Ronald Reagan National Airport (DCA). The FAA temporarily shut-down helicopter traffic on Route 4 and this prohibition was made permanent after the NTSB issued its urgent safety recommendation A-25-1 on 7 March 2025.

Applying the "Swiss cheese" model to this tragic accident, the following circumstances contributed to the midair collision between a CRJ airliner and a military helicopter:

• At 20:33, the helicopter crew requested Helicopter Route 1 to Route 4 , which the tower controller approved.

• At 20:39 the approach controller cleared the airliner for a straight-in visual approach to runway 1.

• At 20:43, the tower controller asked if the airliner could switch to runway 33. After a brief discussion, the crew agreed to this request and the tower controller cleared the airliner to land on runway 33.

  • Note 1: This required a change to the previously briefed plan for approach and landing on runway 1, and a more demanding nighttime, circling, visual approach to runway 33.

• At 20:46, the tower controller informed the helicopter that there was traffic just south of the Wilson Bridge, a CRJ at 1200 ft circling to runway 33. Although at this time the helicopter was about 6.5 nautical miles (12 km) north of the airliner's position and travelling west, the crew reported that they had the traffic in sight and requested to maintain visual separation. The tower controller approved visual separation.

  • Note 2: Upon accepting visual separation, a pilot assumes responsibility for avoiding the other aircraft, based on the principle of "see and avoid"; minimum horizontal and vertical safe separation distances no longer apply.

  • Note 3: The tower controller's transmission was garbled and the word "circling" was not registered on the helicopter's CVR.

  • Note 4: The tower controller subsequently cleared two more airliners to land on runway 1 and the landing lights of these aircraft would have been visible to the crew of the helicopter as it turned to fly south on Route 4.

• At 20:47:39, 20 seconds before impact, the tower controller asked the helicopter if it had the CRJ in sight. A conflict alert in the control tower was audible in this transmission.

  • Note 5: This call and the alarm means that the tower controller was now aware that the two aircraft were on converging courses, but he was still relying on the helicopter to maintain "visual separation". He was probably also relying on an assumed vertical separation to avoid a collision, despite the fact that the radar screen only gives the aircraft's height in hundreds of feet.

• At 20:47.40, 19 seconds before impact, the airliner's Traffic alert and Collision Avoidance System (TCAS) issued an audible Traffic Advisory (TA): "Traffic, traffic".

  • Note 6: A TCAS Traffic Advisory (TA) is designed to activate 20-48 seconds before a potential collision: the crew is required to attempt visual contact and to be prepared to manoeuvre if a Resolution Advisory (RA) occurs. At this time, the helicopter was about 0.95 nautical miles (1.8 km) directly ahead and slightly below the airliner.

  • Note 7: A Resolution Advisory (RA) is designed to activate 15-35 seconds before a potential collision and issues a command to "Climb, climb" or to "Descend, descend"; however, RA's are inhibited below 1000 ft radio altimeter height.

• At 20:47:42, 17 seconds before impact, the tower controller instructed the helicopter to pass behind the CRJ.

  • Note 8: The phrase "pass behind the" was not registered on the helicopter's CVR because of a simultaneous transmission by the helicopter's radio.

• At 20:47:44, 15 seconds before impact, the helicopter indicated that the traffic was in sight and again requested visual separation which was again approved by the tower controller.

• At 20:47:58, one second before impact, the airliner's elevators were deflected to near their maximum nose-up travel and the airplane reached 9° of nose-up pitch.

  • Note 9: This strongly implies that, finally but too late, the airliner's crew were aware of the impending danger, either because they saw the helicopter or responded to the TCAS alert and the graphic indication of a target on its screen.

As highlighted in the notes above, the different circumstances which "lined up the holes in the cheese", were as follows:

1. The tower controller´s request to the airliner to change its approach from runway 1 to runway 33, when he had previously cleared the helicopter to fly Route 4.

2. The airliner crew's acceptance of a nighttime, circling, visual approach to runway 33. The crew were not obliged to accept and had several valid reasons to reject this request.

3. The tower controller identified a potential loss of minimum separation between the airliner and the helicopter, which in VFR is 1,5 miles horizontal and 500 ft vertical. He gave the helicopter crew the type, location, altitude and intended path of the airliner. This induced the helicopter crew to request maintaining visual separation, stating that it had the airliner in sight. However, at night in an urban environment, at a distance of 12 km and with other aircraft heading directly towards you with their landing lights on, it is unlikely that you would correctly identify an aircraft that is now heading away from you on a circling approach pattern. This is even without considering that the crew of the helicopter were wearing night vision goggles, designed to highlight unlit or poorly lit obstacles but with a very limited field of view. The conclusion is that the helicopter crew never correctly identified the CRJ circling to land on runway 33 and in fact probably never saw the airliner because they were focusing on another aircraft.

4. The tower controller missed a last opportunity to warn the crew of the airliner when the collision alert sounded in the tower cab; instead, he again asked the helicopter if he had the CRJ in sight.

5. When the TCAS alert sounded in the airliner's cockpit, the crew should have been able to observe a target at the 12 o´clock position on the TCAS screen, they should have been on the lookout outside and they should have been able to see the helicopter's position and anticollision lights. That they did not see the helicopter in sufficient time to avoid the collision is just another example of the failure of the "see and avoid" concept.

The final "hole in the cheese" was the helicopter's deviation from the maximum height of 200 ft stipulated for this sector of Route 4. According to the NTSB Preliminary Report, at the time of the collision the helicopter was at a radio altitude of 278 ft but it is not clear if the helicopter had a radio altimeter display in the cockpit. The crew would have been relying on the barometric altimeters and about four minutes before the crash the CVR recorded the pilot saying that they were at 300 ft while the instructor pilot (IP) said that they were at 400 ft. Neither pilot commented on this 100 ft discrepancy and this will obviously be part of the continuing investigation.

Notes 3 and 8 highlight another serious flaw in the present ATC system, but I will cover this aspect in my next post.