Bizarre: Flights Receive False Collision Alerts At DCA Airport

There’s certainly some anxiety regarding the airspace around Washington National Airport (DCA), given the fatal mid-air collision we saw several weeks back, which claimed over 70 lives. Along those lines, it was an unusual weekend at the airport, as several planes reported receiving collision warnings, despite no traffic being around.

Erroneous TCAS alerts at Washington DCA Airport

On Saturday, March 1, 2025, several aircraft landing at Washington National Airport received TCAS alerts while on approach.

For those not familiar, commercial aircraft are equipped with TCAS (Traffic Collision Avoidance System), which is supposed to help pilots avoid midair collisions. These alerts come in the form of either TAs (Traffic Advisories), which alert pilots of other planes nearby, or RAs (Resolution Advisories), which give specific instructions about which action pilots should take.

TCAS saves lives, and in most situations, helps avoid any potential midair collisions. But this is also where the situation gets strange, because on Saturday, several aircraft on approach to DCA received TCAS warnings. The good news and bad news is that there weren’t actually any traffic conflicts. That’s good because it means there was no danger, but it’s bad, because it means that something strange was going on.

VASAviation has an excellent video with many of the reports from pilots. One pilot with a TCAS alert said “there was something diving straight onto us,” while another pilot said “it appeared that the target was 600 feet above us.”

Later on, pilots can be heard chiming in with comments like “aliens” and “Russia.” Hah. You can watch the video for yourself below, showing the location of aircraft, plus the air traffic control audio.

The FAA is now investigating this odd TCAS situation

The Federal Aviation Administration (FAA) is now investigating this incident, and has released the following statement:

“Several flight crews inbound to Reagan Washington National Airport received onboard alerts Saturday indicating another aircraft was nearby when no other aircraft were in the area. Some of the crews executed go-arounds as a result of the alerts. The FAA is investigating why the alerts occurred.”

One certainly wonders what could be causing repeated false TCAS alerts, since that’s not something you want to happen, for obvious reasons.

ABC7 interviewed an airline pilot of 40 years about the possible causes, who provided the following insights:

“So there’s only three things I think that could cause it to go off. First is another airplane. The idea that it wasn’t another aircraft leaves it up to the other two, which is either a flock of birds, which is very unlikely, or something on the ground that was transmitting that was causing an erroneous signal that caught several of these airplanes in a row.”

Meanwhile a commenter on VASAviation wrote the following, which is probably a more technical explanation of that last point above:

“This can happen if an ADSB system on the ground is not filtering ‘ownship’ traffic properly. Had this happen near KCOS airport (Colorado Springs) a year ago. The consistency tells me it is the same thing. If you understand how this system works, it is clear what happens when filtering from the ground stations are not done properly. On board equipment interprets your ship as a separate target, unknown, and right on top of you.”

This is way beyond my area of expertise, though it’s pretty remarkable that this is happening at the same airport where a mid-air collision happened just weeks ago. Is that a coincidence, or…?

Bottom line

On Saturday, several aircraft on approach to Washington DCA reported receiving TCAS alerts, despite there being no traffic in sight. The FAA is now investigating the cause of this, since it’s of course important to minimize the number of false TCAS alerts, given that TCAS is basically the last defense against collisions.

What do you make of this strange TCAS alert situation at DCA?