On the 11th of March, the NTSB released an aviation investigation preliminary report on the mid-air collision between PSA Airlines flight 5342 and a Sikorsky UH60L US Army helicopter. At the same time, they released an an urgent recommendation report calling for the FAA to close the helicopter route that the military helicopter was following whenever runway 33 is in use.

This report shows that the separation between the aviation traffic for runway 33 and helicopters on route 4 was dangerously tight. In short, this was an accident waiting to happen.

Ronald Reagan Washington National Airport (DCA) is located in Arlington, Virginia, five miles (eight km) from Washington DC.  The airport has three runways: runway 01/19, runway 15/33 and (not relevant to this case) runway 04/22.  The main runway in use at Washington National is runway 01/19 (north/south), a 7,169-foot (2185-metre) asphalt runway.

Runway 15/33 (south-by-southeast/north-by-northwest) does not have the landing distance of 01/19, with 5,204 feet (1,586 m) of asphalt. It is used for smaller aircraft and sometimes for overflow from the busier north/south runway. In addition, based on wind conditions, larger aircraft will specifically request runway 33, because the turn-off points are located closer to the terminals, which means less taxying to get to the gates. On busy days, runway 33 may be used to deal with heavy traffic and keep separation.

On that day, the 29th of January 2025, runway 01 was in use, allowing for northbound landing and departures. This means that arriving traffic is coming in from the south of the runway, with occasional traffic coming from the southeast and crossing the Potomac for runway 33.

There is a lot of helicopter traffic around the DC area, airspace which requires special approval as a result of the government sites and military bases in the area. Standard helicopter routes, first charted in 1988, have been defined for crossing the Washington DC airspace, numbered from 1 to 4. These routes have particularly low altitude restrictions to avoid conflicts with commercial aviation in the area. In New York, for example, the altitude restrictions range from 500 to 1,000 feet above mean sea level, while the DC area has maximum allowable altitudes as low as 200 feet amsl.

Route 1 starts at the American Legion Bridge near Cabin John, Maryland and follows the western shore of the Potomac until Key Bridge in Washington DC. Here, the route crosses the river to avoid prohibited airspace, following the eastern shore with the Kennedy Center and Lincoln Memorial visible to the east and Rosslyn to the west, to Memorial Bridge.  From here, helicopter traffic must remain at or below 200 feet above mean sea level. The route continues south of the Washington Monument, where it leaves the river’s shore and crosses the Tidal Basin to follow the Washington Channel along East Potomac Park. Hains Point, at the southern tip of East Potomac Park, is directly across the river from the north end of Washington National airport.

Route 1 has two reporting points.  Memorial Bridge, where the helicopter may cross to join Route 5 or continue to turn over the Tidal Basin, is a compulsory reporting point: pilots must report to air traffic control that they have reached that position as they follow the shore of the Potomac. Hains Point is a non-compulsory reporting point: pilots are not required to report passing the landmark, but the controller may request that they do so.

From Hains Point Route 4 continues south, parallel to the Potomac River and runway 01/19.

The FAA’s Helicopter Route Chart shows clearly that a helicopter following Route 4 would cross the approach path for runway 33. Vertical separation is accounted for by keeping the helicopter between 100 and 200 feet. An aircraft descending on a 3° slope would pass this point at 300 feet.

This does not offer a lot of leeway. A further issue at this intersection is that the fact that Route 4 follows the eastern shoreline of the Potomac, but there’s not a specifically defined distance that  the helicopter needs to be from the shore. So a helicopter following the shoreline further over the water may have even less separation from the descending aircraft on finals for runway 33.

This graphic from the NTSB shows how the vertical separation narrows. If everyone does everything perfectly but they arrive at the same lateral point at the same time, at best, the vertical separation is only 75 feet. If the helicopter is a bit further from the shoreline or a dozen feet above the maximum allowable altitude or if the aircraft is slightly below the 3° glideslope, the vertical separation becomes dangerously small.

The Swiss cheese model is used to show even with many layers of defence against accidents, each layers has flaws that, if aligned, can lead to the accident bypassing all defences.  Looking at the helicopter route and the approach path for runway 33, we can already see the holes in the cheese lining up.

Now to be fair, aircraft are not usually arriving on runway 33.  Over the period of the past six years, runway 01 accounted for 57% of all arrivals while runway 33 accounted for just 4%.  Still, when the ATSB looked at the voluntary safety reporting program, they found a disquieting number of reports of near misses between helicopters and commercial aircraft, the vast majority of which were reported as on approach to landing.

There are a number of protections in place against mid-air collisions, including TCAS (Traffic Collision Avoidance System). TCAS is standard in modern commercial transport aircraft, with TCAS II _required _on all commercial aircraft in the US with more than 30 seats or over a certain take-off weight. TCAS is independent of air traffic control and serves to alert flight crew to the threat of collision when, for whatever reason, the standard systems have failed to provide the necessary separation. It scans all nearby aircraft and sounds a traffic advisory (TA) to alert the flight crew of nearby aircraft of potential conflict. The TCAS traffic display gives the flight crew a chance to locate the other aircraft visually and prepare for the next instruction. The next instruction if needed, would be a resolution advisory (RA), in which TCAS gives a mandatory instruction to the pilot, usually to climb or descend, in order to increase (or at least maintain) the amount of vertical separation between the aircraft.

The point is that once a resolution advisory is triggered, something has already gone wrong and the aircraft are already dangerously close.

When the NTSB looked at the near-miss data in the reporting program over the period from October 2021 to December 2024, they found over 15,000 cases where the lateral separation of less than one nautical mile and a vertical separation of less than 400 feet.  Total operations for that period were 944,000 commercial operations (IFR departures and arrivals).  Further, there were 85 records with a lateral separation of less than 1,500 feet and vertical separation of 200 feet. They discovered that every month, at least one aircraft TCAS resolution advisory was triggered by a nearby helicopter.

Here is another hole in the cheese. When an aircraft descends below 900 feet on final approach to land, TCAS stops issuing resolution advisories. This is for very good reasons: automatic commands to climb or descend could direct aircraft too close to terrain or into the path of airport traffic. At low altitudes, the system provides only traffic advisories without giving potentially dangerous instructions to climb or descend. Below 400 feet, even these audio alerts are silenced, to prevent distraction during this most critical phase of flight.

As Philippe explained in the comments of my initial piece:

I’m typed in the CRJ and I’ll have to correct myself regarding my last comment, as I’ve just read it up in the OM-B: While only RAs are inhibited below 1000′, TAs are inhibited below 400′ in descent (and 600′ in climb). Additionally, TAs are not created for targets below 380′.

The crew should have received a TA regarding the first inhibition (the A/C would have been above 400′ when the helicopter became an intruder), but as the collision apparently occurred at 200′, the helicopter would have been too low for a TA. Really a tragic event.

This means that this critical intersection of helicopters on Route 4 and aircraft on final descent to 33 did not have TCAS protection: maintaining vertical separation relied entirely on ATC coordination and visual separation, by design.

On that evening, the  Sikorsky UH-60L crew filed a flight plan for a night flight from Davison Army Airfield for the pilot’s annual standardisation evaluation with the use of night vision goggles. The pilot was a captain with 450 total hours, 326 of which were on the same helicopter make and model. The pilot was accompanied by an instructor pilot, with 968 total hours, of which 300 were on type, and a crew chief, with 1,149 total flight hours, all of which were on UH-60 helicopters. The helicopter used the callsign PAT25.

At 20:33, PAT25 was 15 nautical miles northwest of Washington National Airport. The flight crew requested Route 1 to Route 4 before returning to Davison Army Airfield, which was approved by the controller. Note that there are two frequencies, one for the helicopter traffic and one for the commercial traffic, which were normally manned by separate controllers during the evening and then combined into one position after 21:30, when the traffic was not as heavy.  However, there is a shortage of air traffic controllers at Washington National Airport (and most of the US air traffic control facilities). One news report said that the ATC unit there should consist of 30 controllers but in fact, there are only 19.

That night, one controller asked to leave early and the two positions were combined early. Thus, one controller was managing all of the helicopter and commercial aircraft traffic in the airport’s area during a busy time.

A CRJ700 operating as passenger flight PSA Airlines 5342 from Wichita, Kansas, was inbound to Washington National Airport. Both pilots in the CRJ held Air Transport Pilot Certificates. The captain, who had 39,050 total flight hours of which 3,024 were on the accident aircraft make and model, was the pilot flying. The first officer, with 2,469 total hours of which 966 were on the aircraft make and model, was the Pilot Monitoring.

About ten minutes after the helicopter started on Route 1,  PSA Airlines flight 5342 contacted the tower controller to say they were 10.5 nautical miles south of the airport and on the Mount Vernon visual approach to runway 1. The controller asked if they would accept runway 33 for landing, which the flight crew was happy with.  Having the CRJ land on runway 33 allows the controller a bit more leeway for managing traffic on runway 01. As Mendel explained on the previous post:

Scenario 1: Aircraft 1 (A1) lands on runway 01. It needs to slow down at the end of the runway, and then find a taxiway to get off the runway, before it is safe for aircraft 2 (A2) to land.

Scenario 2: Aircraft 1 lands on 33. Once it is past the intersection with runway 01, it’s safe for aircraft 2 to land on 33. The rollout etc. of A1 does not affect A2.

In scenario 2, the aircraft can be spaced closer and will still be safe from each other.

At this point, flight 5342 was travelling north along the Potomac River. The helicopter, travelling south along Route 1, was just crossing the Tidal Basin.

At 20:46, the controller asked the helicopter if they had visual contact with flight 5342.

Tower Controller: PAT25, traffic just south of the Woodrow Bridge, a CRJ at 1,200 feet setting up for runway 33.

Helicopter: PAT25 has the traffic in sight. Request visual separation.

Tower Controller: Visual separation approved.

Visual separation means that the pilot assumes the responsibility for maintaining a safe distance from another aircraft that they can see. This allows for less separation as well as reducing the controller’s workload. Requesting visual separation once you have the aircraft in sight allows for more flexible operations, as you can manoeuvre as needed to ensure that you don’t get too close.

The tower controller cleared a jet for departure from runway 01.

As the helicopter passed south of Hains Point, the controller asked again for the flight crew to confirm that they had the descending flight in sight.

Tower Controller: PAT25, do you have the CRJ in sight?

No response. About four seconds later, the controller checked in again with the helicopter.

Tower Controller: PAT25, pass behind the CRJ.

Helicopter: PAT25 has the aircraft in sight, request visual separation.

Tower Controller: Vis[ual] sep[aration] approved.

Twenty seconds later, at 20:47:59, at an altitude of 300 feet, the helicopter flew into the passenger jet. Both aircraft plunged into the Potomac, killing all crew and passengers on board.

Much has been made of the fact that the helicopter was 100 feet above the maximum allowable altitude. However, it is clear from this analysis that within the Washington DC airspace, aircraft and helicopters were placed on intersecting paths with minimal separation. Operations were designed with minimal safety margins, creating a system where pilots and controllers had to perform perfectly every time to avoid disaster.  Controller staffing issues led to a reliance on visual separation during night operations in a situation where TCAS support was limited.  The frequency of TCAS alerts and near-misses reveals this wasn’t an isolated incident but a predictable outcome.

Six days after the accident, the FAA restricted helicopter traffic from operating over the Potomac River near Washington National Airport. The current notice to airmen (NOTAM) (FDC 5/4379) holds until the 31st of March and if a helicopter must operate in that area (for example a life-saving medical flight, active law enforcement or air defence, or a presidential transport helicopter mission), then no civilian aircraft will be allowed to proceed through the area until the helicopter is clear.

The NTSB preliminary findings underscore this decision, showing that existing separation between helicopter traffic on Route 4 and aircraft descent paths for final approach on runway 33 are insufficient.  In fact, the NTSB statement says outright that the existing situation poses an intolerable risk to aviation safety. They concluded that we simply cannot safely allow helicopter traffic on the existing Route 4 when aircraft are landing on runway 33.

The investigation is ongoing, however two urgent recommendations have been released asking the Federal Aviation Administration, primarily that helicopter operations on Route 4 be permanently prohibited between Hains Point and the Wilson Bridge whenever runway 33 is used for arrivals (and when runway 15 is used for departures).

Closing helicopter Route 4 when runway 15/33 is in use has a clear downside: this is a much-used corridor through the area. Losing it will cause issues for law enforcement and government operations (medical evacuation flights would not be affected, as they are always prioritised). Further, asking helicopters to hold for the corridor to become available also carries risk, notably in this case by increasing the controller workload even more.

Thus, the NTSB’s second urgent recommendation is for the FAA to devise an alternative helicopter route which would allow for travel in that area when runway 15/33 is in use and Route 4 is closed, allowing helicopter traffic to travel between Hains Point and Wilson Bridge.

These recommendations acknowledge that safety systems must be designed to accommodate human factors and operational realities. Aviation has become remarkably safe precisely because of multiple layers of protection. However, care must be taken that this protection does not demand flawless execution: aviation safety requires tolerance for minor mistakes without catastrophic consequences.

This tragic accident revealed just how thin the margins for error had become around Washington National Airport. The helicopter routes designed almost forty years ago became more and more dangerous as aviation traffic intensified and controller staffing declined. The data showing monthly TCAS alerts and thousands of close encounters demonstrates that this wasn’t an isolated incident but a predictable outcome of system design.

The urgent recommendation from the NTSB targets the immediate danger. However, the fact remains this high-risk intersection was allowed to persist for years. As the National Airspace System grows increasingly complex, airspace design and controller staffing at busy airports must be reassessed to create breathing room for human error.

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