To you and everyone else talking about TCAS:
I currently use TCAS every day. It uses a directional antenna to determine the position of other aircraft. That is not very accurate, especially during turns as the displayed position lags behind where it should be.
Of course the traffic display is not to be used for avoidance maneuvers. And RAs are inhibited below 1000’. (Perhaps that should be changed to only give UP commands below 1000’.)
However in my previous job at a 135 operator we had ADS -B IN, and the position of other aircraft as displayed was always very accurate.
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Was not addressing TCAS, was ref’ing my experience with ADS-B in a busy maneuvering environment…in the mishap scenario with significant bearing shifts between system updates, there could be additional distraction caused by ADS-B lagging the visual picture.
Not an implication of GPS (that has its own issues around nefarious actors…), GPS position is accurate at time of ADS-B system receipt but the network that provides ADS-B input is subject to receiver dropouts (causing jumpy targets), delays imposed by ATC transponder interrogator sweep rate and end to end network transit. I agree it is useful for building SA and working around other slowly evolving traffic conflicts, it’s less useful and sometimes distracting at tactical ranges where there is significant bearing shift (in close or dynamic maneuvering).
Accuracy and latency depend on the source type. Actual ADS-B (aircraft to aircraft) won’t have more than about 2 seconds of lag (1.4 uncompensated) per FAA MOPS. At approach speeds in the CRJ that’s what… 150 meters max error? That’s a much more accurate view than the approach control radar readout in the tower.
Other traffic sources that come across the ADS-B system have greater lag: ADS-R (rebroadcast by the ground stations of 1090->UAT and UAT->1090); TIS-B (uplink of SSR targets without ADS-B Out capabilities). Those targets are identified as such in the stream and could be painted with a somewhat more “fuzzy” position or discarded.
The hard part is implementation. Adding ADS-B In is possible on both the civilian and military platforms (ForeFlight + receiver), but incorporating the data into something that would be useful and actionable while on final approach would be much more challenging and expensive.
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Arthur, ADS-B was introduced to improve surveillance, separation, increase coverage and efficiency, and safety – not as a standalone collision avoidance system. The DCA midair isn’t just about non-compliance, it’s about the fact that the system itself is incomplete.
ADS-B Out is required, but ADS-B IN is not, and there’s no regulation mandating integrated conflict alerts or resolution advisories. While IN capability is widely available and encouraged, it’s not required – and without it, the system becomes one-way. It broadcasts, but it doesn’t prevent.
To make matters worse, there’s no mandatory performance check for ADS-B equipment. A system can silently fail for years – as may have happened here – and no one would know. Unlike transponders, there’s no §91.413-style verification.
And then there’s the question of perception. The helicopter’s callsign – PAT25 – designates a U.S. Army “Priority Air Transport” mission. That kind of designation can carry weight with ATC, possibly influencing how closely the flight’s compliance or track integrity was monitored. It’s not about rule-breaking – it’s about the quiet pressure to defer to a military priority flight, even when something looks off. That’s human nature, and it’s part of the larger picture.
Blaming ADS-B misses the real issue. The current rules don’t go far enough, and the implementation doesn’t guarantee safety. If anything, the DCA incident shows what happens when we rely on a system that’s only half built – and on assumptions that everyone is always in the loop.
That’s the real gap – and it needs to be addressed.
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My concern throughout this thread is that while everyone argues over the tech implementation, the real issues are policy/procedure.
Policy, the same people demanding someone’s head (Congress) are the same ones who legislated traffic flows in excess of what was safe.
Procedures…jamming traffic thru a chokepoint with multiple near misses reacted/reported and then being surprised at the outcome. Multi-runway ops during helo transit at night, helo night training during airline ops…and why not re-route “national missions” thru prohibited airspace for some extra breathing room?
Tech is NOT the answer…fix “stupid” first.
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" improve surveillance, separation, increase coverage and efficiency, and safety " That’s what I said, and I’m pissed about that I had to cough up real money for a mandatory piece of equipment that is not even being used in the most critical airspace in the country. What’s the frigging point if it’s not being used even in the most restricted airspace AND is not improving separation/safety? Ahrg, Madness.
I question why, on a crystal clear night, two cockpit crews had their heads inside the cockpit (likely elsewhere) and didn’t see each other until it was too late to avoid a collision.
Sorry, TCAS is not more accurate than ADS-B.
If interested, my recollection of how we got here with ADS-B
So, way back when Next Gen was being hyped, FAA was all aflutter about cost shifting by shutting down most of their ATC/Nav terrestrial resources…expensive, complicated, things (radar, VORs, etc) located in remote areas, difficult and expensive to maintain. DoD provided the GPS for free and users provided the sensor (ADS-B out) for free (from FAA’s view)…this was “from space (GPS based)” so only luddites (like us) would be against it. The “revolution” would enable larger more efficient traffic flows thru the system, saving the planet with energy managed flight paths…except the requirements wizards missed a few things…system throughput is not limited by airspace as much as by chokepoints driven by the finite number of runways…anyone want to get out there and sell more runways or new airports to the local populations and Reps? and dynamic routing sounds good until the acft start flying over different neighborhoods.
Then there was the assumption that because the FAA said so, everyone would dutifully turn on their ADS-B out at all times…that assumption left the building on 9/11 when transponders were turned off and the only tracking was primary radar (skin paint)…that led to budget chicken between DoD and FAA over who was going to pay for the radar coverage, DoD brought a requirement for skin paint coverage within US, up until then, concern was exclusively outward looking…bring a requirement, better bring a checkbook.
ADS-B was the carrot to get more of us to play and a means to extract a fig leaf for all the sunk cost. And “Free Flight” (the hyped concept name if I recall correctly)…looked a lot like VFR, so go enjoy that while we can!
ADS-B has the infrastructure to support safer airspace, but as currently deployed, it lacks critical components to detect, alert, and prevent. Without ADS-B IN, alerting, and oversight, ADS-B remains a surveillance tool – not a collision avoidance system. To treat it as complete without these elements is a systemic risk.
Then imagine the additional costs to users – especially GA and small operators – to retrofit, upgrade, and maintain systems just to reach the safety level that many already assume exists. Without a full strategy, we’re shifting responsibility without delivering the capability.
I agree with RICH_R; “Tech is NOT the answer…fix “stupid” first.”
A part 91 operator who operates in the 30 mile veil “must have” ADS-B out. Once installed, it may not be turned off, except possibly in class G.
https://www.ecfr.gov/current/title-14/part-91/section-91.225#p-91.225(f)
However: each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times unless—
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URL
https://www.ecfr.gov/current/title-14/part-91/section-91.225#p-91.225(f)
Citation
14 CFR 91.225(f)
…each person operating an aircraft equipped with ADS-B Out must operate this equipment in the transmit mode at all times unless—
(1) Otherwise authorized by the FAA when the aircraft is performing a sensitive government mission for national defense, homeland security, intelligence or law enforcement purposes and transmitting would compromise the operations security of the mission or pose a safety risk to the aircraft, crew, or people and property in the air or on the ground; or
(2) Otherwise directed by ATC when transmitting would jeopardize the safe execution of air traffic control functions.
This is where the problem lies. Political actors wished to hide certain aerial operations from the unwashed masses. How simple would it be to direct a drone to intercept a given ICAO code broadcast over 1090 or 978 Mhz with altitude and trajectory information squitted out every second? Of course this will likely be our next 911. This probably is the reason for the most recent “upgrade” to hiding aircraft registration information. Someone in govt. realized the total degradation of security for the flyover crowd. (thanks Elon).
Law enforcement will pay Garmin thousands to enable the ADS-B turn off mode (G1000), so they can loiter at 5000 feet with a stingray or IMSI-catcher. The “surveilled” could use flight aware ADS-B data to determine the likelihood of aerial surveillance. (same N number over your house for hours every day)
To really make this stuff work as it does in the pipe dreams, you need something like this, from Freeflight: “Combining TCAS II (Traffic Collision Avoidance System) with ADS-B In enables hybrid surveillance, enhancing the reliability and performance of collision avoidance systems. With both systems integrated and displayed on the same cockpit interface, pilots can manage traffic information more efficiently and receive more precise and timely traffic alerts and resolution advisories, significantly reducing their workload and enhancing coordination, especially in busy airspace.”
In my mind, I wonder if the military ran “911 intercept” missions at passenger carrying aircraft in the DCA airspace… That would explain the number of separation incidents better than anything. I don’t submit that the subject accident was a mission of that type, however.
There are additional enhancements available with certified ADS-B in.
AC90-114C defines them. https://www.faa.gov/news/stay_connected/
AC20-172B and TSO 195c also address these systems.
Certain airlines with were able to get waivers regarding WAAS GPS data (they, but not GA, could use TSO C129a and C196 for ADS-B circa the 2020 mandate). (Exemption No. 12555)
I certainly hope this CF gets fixed, but I am not holding my breath.
I totally agree with Rich R’s post combined with BBGun and sskol’s comments to his post. Jump there for the TLDR picture.
I don’t think the AAL crew can be faulted. They were on a fairly short final with both sets of eyes probably focused on the runway or configuring further. Probably the folks who saw what was about to happen were the passengers on the right side. They would have been sightseeing the capitol area looking at DC. And I’m guessing the lights of the helicopter rapidly approaching. If anyone of them was a pilot I imagine he/she would be thinking what is going on with this. The copter crew, yes. Not a good place to train without your head on a swivel.
Too many things that could have gone wrong went wrong. It’s not just a “Swiss cheese model” – it’s a stack of holes flying formation.
I, too, wondered how the flight path of PAT25 showed up online almost immediately after the accident if their ADS-B wasn’t on. Thinking about it, however, I remembered that when I put in my GTX335 I flew it with ADS-B turned off (in rural airspace) and still saw my path on Flight Aware as if it was on. THAT was when I learned about “multilateration.” Essentially, there are SO many ‘sniffers’ out there that Flight Aware can combine the time of receipt information to calculate your path. Don’t forget that ADS-B is called Mode S ES (extended squitter). Even if you turn off ADS-B out (ES), you’re still transmitting your N number because the transponder is a Mode S box. ES if off but N number is still on on Mode S. SO … I assume whatever mode PAT25 was transmitting with, it’s call sign was known and seen by ATC and multilateration did the rest IF ES was off? Elsewhere, I read where the Army routinely doesn’t turn on ADS-B. Maybe they don’t realize that their call sign is still known on priority missions? When you look at Flight Aware for your airplane, it’ll tell you if it’s using ADS-B (ES) or multilateration.
I watched the Congressional dog-and-pony show on CSPAN on March 27th. One of the Senators was complaining that ADS-B ‘in’ is not mandated but should be. Jennifer Homendy said that NTSB has recommended that since 2008 and the acting FAA Director said they’ll consider it. I am AGAINST that. Once FAA mandates equippage, the equipment will have to be TSO’ed driving the cost to all up exponentially. Currently, most folks with out have some form of in sniffer and either an iPad or GPS that’ll feed either an iPad or GPS display. It’s smarter to ‘strongly recommend’ ADS-B ‘in’ equipment for all. Much like the recent FAA SAIB recommending installation of AoA equipment via NORSEE rules.
I agree with Raf that without ‘in,’ ADS-B isn’t a collision avoidance tool. I read where the Army didn’t have enough iPads to equip all their copters with ForeFlight or? so they rarely used it. I plan to email the Commander of the owning Army unit as well as copy BGen Braman with a recommendation. Why not have a number of Garmin GDL50 ‘in’ sniffers along with either Aera660 or 760 GPS’ set to traffic pages in front of both pilots and maybe even the crew chief on missions in congested airspace?. Imagine on this flight if both pilots were on NVG’s but the crew chief in back had a small display and knew how to use it. HE coulda alerted the crew to the traffic. There are SO many coulda, shoulda, woulda things that would have changed the outcome of this sad event.
Finally, some have commented on use of the Public ADS-B Performance Report. Recently right here on Avweb, Larry Anglisano recommended doing those routinely. They’re free, easy to do and provide confidence that you’re gonna meet 91.225. I do it before every flight that requires ADS-B to be operating. And, remember, IF your Mode S ES (out) is turned off, ATC can STILL ID you via the Mode S part of your transponder.
I didn’t comment on altitude.
On a Mode S ES transponder where ADS-B is turned off but the transponder is on, your altitude is also still being transmitted along with your Flight ID. Sniffers in nearby airplanes can ‘hear’ you but do not know where you are because lat, long, et al, are part of the ES data stream. So you’re not directly seen by them. The FAA radars would have to see you and retransmit your info to the ADS-B receiver … inducing a delay, among other things, in the process as long as you’re in the 30nm ‘hockey puck’ piece of airspace.
Most GA airplanes use ‘blind encoders’ vs a combo altimeter that puts out altitude and a digital equivalent of same in one instrument. That’s why they’re called "blind.’ YOU can’t see what they’re doing and there could be a big difference between the altitude a pilot is flying using the altimeter and the altitude ATC sees on their scopes. Likewise, not setting your Kollsman window to a nearby setting can induce a difference because a blind encoder is set to sniff out PRESSURE ALTITUDE (29.92). ATC computers apply the correction factor to pressure altitude they see on your transmitted info to what the pilot would see on the altimeter. Older parallel output encoders (e,g, Narco AR850) only digitize your altitude in 100’ increments and are still legal. Newer serial encoders digitize altitude down to (I think) 10’ increments? However, it’s better than 100’. There is a requirement for the blind encoder and the altimeter to “correspond” within 125’. IF you aren’t doing a full IFR checkout of your transponder system because you fly VFR, they only check that the encoder is working and is showing field altitude. So between failure to set the correct altimeter setting in the Kollsman window and calibration factors on the encoding device installed and the allowable 125’ error, I wouldn’t fly anywhere where 75’ to 100’ separation was normal!
What I do is occasionally fly up to 10K’ and take notes as to the altitude seen on my altimeter vs. that seen on my transponder display every 500’. This is a confidence maneuver for me along with doing a PAPR. That’s one of the advantages of having a panel mounted transponder where you can see what it’s transmitting. To know if it’s right, you’d have to set your altimeter to 29.92 and see what the difference is since the blind encoder cannot be adjusted.
Sounds like the Army wasn’t doing any of these things? So the altitude being reported problem may well have been the type of encoder system installed in those helicopters along with the lack of ADS-B being on. And if the airliner didn’t have a way to ‘see’ traffic’ via ADS-B ‘in’ … there’s your problem. It’s a miracle that this accident didn’t happen sooner …
It would be smarter and safer to require all helicopter and military flights stay in MOAs and never in any metro area. All training should be in MOAs or uncontrolled airspace. I always thought this was the case until this accident. Helicopters doing training inside class B airspace is unlawful. Why is this issue still around?
Barn Door - Closed
Horses - Long gone, died of old age, sent to glue factory
Thank Larry, I had hope youd’d get into the discussion. 
On American Airlines Flight 5342. The crew did nothing wrong, but the airline and industry can still lead improvements in tech, training, and policy to prevent another tragedy.
Funny, Raf … I presumed that … glad to help all 
First off, the statement “FAA Acting Administrator Chris Rocheleau announced that the agency will require most aircraft operating around Ronald Reagan National Airport to have ADS-B technology activated.” may be the most ridiculous thing I’ve ever read on avweb. This is a statement that has been true since the ADS-B mandate, this airspace has always been subject to that requirement for aircraft that don’t get “the pass”. So it seems business as usual continues, they’ll still be giving a pass on ADS-B use to some aircraft, why?
Second, most of the discussion here, while informative, is pointless. This didn’t happen because of a lack of ADS-B in or out, it didn’t happen because of TCAS being disabled below 1000’, it happened because the helicopter was somewhere it should have ever been allowed to be and it was all legal. Let’s admit that the FAA is the party primarily at fault for this accident. Someone at the FAA been signing off on chart revisions for years, possibly decades, with an obviously dangerous conflict between routes in plain view. I have been unable to determine when that helicopter route was first published, and I don’t fly up there so I don’t exactly have a pile of old charts to look at, but that route never should have been approved in the first place. Military helicopters never should have been given the option to continue on their way directly across an active final with “visual separation”, especially when there’s a military base they can safely overfly right on the other side of the river and a highway they can overfly just beyond that. There was no requirement to hold at a point or divert if the final was active, no nothing, just fly right under an active final with right of way aircraft turning left and blind to the approaching helicopters. In my eyes, 67 people are dead because the FAA decided that deferring to military operations in congested airspace with seemingly little more than “they can handle it” was acceptable. The military wants to fly training flights there? Too bad, they can train in one of their dozens of MOAs. VIP transport flights? Too bad. Make them coordinate it with ATC and fly around active finals, the VIP can be late to his meeting with lobbyists. The saddest thing about this accident was that there is no remotely good reason for it to have happened. All they had to do deviate the route around the active finals, overflying a military installation instead, and 67 people would still be alive today.
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