NTSB: Sonex In Colorado Midair Was Not Transmitting ADS-B ‘Out’ Data


Contrary to previous reports, the Sonex Xenos involved in the Sept. 17, 2022, triple-fatal midair collision in Colorado was not transmitting ADS-B “out” data at the time of the accident, according to the NTSB. ADS-B “out” is required within the Denver Mode C veil where the accident occurred. And the NTSB Preliminary Report (download PDF here) further states the aircraft’s last flight during which it broadcast ADS-B data was flown on July 14, a flight lasting six minutes, according to FlightAware.

Between that date and the accident date, FlightAware (which gets its data from numerous sources, including air traffic control and ADS-B) recorded eight more flights originating from the Sonex’s home airport (Platte Valley Airpark—18V), which lies well within the Mode C veil. The flights ranged in duration from 12 minutes to just less than an hour.

Both aircraft involved in the accident, the Sonex and a Cessna 172 Skyhawk on a training flight with two on board, were squawking VFR (1200) transponder codes. According to the text of the NTSB report, “Both airplanes operated within the Mode-C veil of the Denver International Airport Class B airspace that required automatic dependent surveillance broadcast (ADS-B) ‘out’ transmissions. The Cessna was equipped with ADS-B ‘in/out’ equipment and transmitted ADS-B data during the accident flight. The Sonex did not transmit ADS-B data during the accident flight …” Neither aircraft was in radio contact with ATC, nor were they required to be.

From the report: “A review of air traffic control (ATC) flight track data revealed the Cessna departed Rocky Mountain Municipal Airport (BJC), Denver, Colorado, about 0843, and the Sonex departed Platte Valley Airpark (18V), Hudson, Colorado, about 0838. The airplanes climbed to about 7,000-7,500 feet mean sea level (msl) [approximately 2,000 feet above ground level] and were operating under visual flight rules (VFR). The Cessna flew northbound and the Sonex flew westbound toward the Longmont area. After the Cessna completed a left 360-degree turn, it turned eastbound. The flight track data of the two airplanes merged and subsequently showed both airplanes rapidly descending.”

The FAA-registered owner of the Sonex, Henry Butler Jr., was the pilot on the accident flight and the sole occupant. According to FAA records, the aircraft was registered on Feb. 24, 2022. The previously listed owner was a limited liability corporation in Wisconsin. The corporation was listed as the registered owner from August 2016 until October 2021 when the aircraft was listed as “Registration Pending.”

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Mark Phelps is a senior editor at AVweb. He is an instrument rated private pilot and former owner of a Grumman American AA1B and a V-tail Bonanza.

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  1. This news is disturbing. I wonder what specific ADS-B equipment was on the Sonex. And that leads to another question: was that equipment capable of indicating when it was NOT operating correctly? My thinking is that the pilot was unaware of the faulty equipment, rather than flying without it.

    • That the Xenos was squawking 1200 (so the subsequent ATC accident data replay ‘saw’ him) and — at a prior point in time — DID transmit ADS-B information leads me to conclude that he MAY have had one of the ADS-B systems that “sniff” the transponders selected code and pressure altitude but failed to turn it on. So the pilot DID turn the transponder on but … for some reason … the ADS-B wasn’t on. The uAvionix tail beacon or wing tip beacons REQUIRE that the position lights be on because that’s where the system gets its power from. Just the other day, a local pilot had one of those systems installed; it HAS a decal that is installed in view of the pilot informing he/she that the position lights must be on for ADS-B to be operable.

      I’d be willing to bet a few bucks that the pilot didn’t know that the ADS-B wasn’t on unless the position lights were on IF that’s the type of system that was installed.

  2. I don’t see the relevance of no ADS-B out data in airspace that communication with ATC was not required, with this accident. ADS-B out data does not have the legal authority like TCAS does. You still need to be looking outside the window in a traffic pattern, not heads down trying to figure out what the ADS-B out display is showing on the panel, if you have one.

    • It’s relevant because it’s a layer of safety that failed. It’s not the end all-be all of what caused the accident but it’s a contributing factor. And before the old luddites start pounding on me, I do keep my eyes outside the cockpit, but what everybody always forgets is that the vast majority of us are using Foreflight which gives an aural warning when traffic is close. That may have well been enough to prevent this from happening if all equipment had been working.

    • It is very relevant. I fly in congested airspace and always look for visual targets when VFR. That said, flying every week, I usually see the target on my screen first, which gives me an area in which to identify the target visually. I would expect, given that this was an instruction flight in the 172, that the flight instructor would also keep an eye on the screen. A light illuminates on my panel in the event of ADS-B failure. Many lessons learned here.

    • Yes, we all must be vigilant looking for traffic. Our eyes love to see movement, traffic moving against a contrasting background is eye candy. Traffic on a collision course will have no relative movement to draw your eyes to it. It will be a small dot on the windshield (a bug spot) or behind the canopy bow that suddenly gets a lot bigger. I don’t count on ADS-B traffic, but I’m more likely to spot the traffic on a collision course, when ADS-B announces “Traffic, 1 o’clock, 1 mile, level” before the spot suddenly gets a lot bigger.

    • From the preliminary accident report: “At the time of the accident, both airplanes transmitted a transponder code of 1200 (VFR) and neither airplane was in radio contact, nor was required to be in contact with ATC. [U]Both airplanes operated within the Mode-C veil of the Denver International Airport Class B airspace that required automatic dependent surveillance broadcast (ADS-B) “out” transmissions.[/B]
      The Cessna was equipped with ADS-B “in/out” equipment and transmitted ADS-B data during the accident flight. The Sonex did not transmit ADS-B data during the accident flight;…”

      ADSB/OUT, as a minimum, was required in the airspace. The pilot/operator of the Sonex was not complying with the requirements and was therefore negligent. He was responsible for knowing certain miminimal tasks, included among ’em were how to operate his aircraft’s ADSB/OUT equipment since it was needed to comply with ADSB requirements inside the Class B veil. He and the Cessna crew also failed to exercise effective see and avoid. IMHO, the tipping factor, in this midair was likely the Sonic pilot’s failure to squawk ADSB/OUT.

  3. Sad all around. But criminal negligence comes to mind on the part of the Sonex pilot.

    As a local CFI that’s spent many hundreds of hours over the very spot where this accident occurred, ADSB is used heavily by pilots in this area. 98%+ chance this accident wouldn’t have happened if the Sonex had had ADSB-out enabled, nearly every full time CFI in this area uses this data to help deconflict in this practice area, especially those from the technology generation.

    • “Criminal” usually comes to mind these days whether we’re talking about ADS-B or sitting in your car eating a cheeseburger.

      Neither aircraft were required to be in contact with ATC. Both aircraft were required to transmit ADS-B however, neither aircraft were required to monitor ADS-B in. At this point in the reporting, there is no indication that the Sonex did not have his ADS-B on.

      Both pilots were required to see and avoid.

    • You say criminal “negligence” so I’ll give you the benefit of the doubt of suspecting owner/op or mechanic giving the go on a failed transmitter. Besides that, other criminal would need some kind of motive, and none comes to my mind in this situation.

    • ADS-B is great as a strategic tool to look ahead and see if other airplanes might be in your path, but using it as a tactical tool is very problematic. If “nearly every” CFI is staring at their screens for traffic avoidance, I would say there is a huge problem. Technology can fail any time, and we should not be training our next generation to bet their lives on gadgets working correctly.

    • I’ve gotten in a lot of arguments over levels of negligence. IMO, the terms are confusing and ought to be changed. Of course, we’ll never get to put the legislators and lawyers in jail for their negligence, so I guess the terms will not change.

    • This accident was a tough one for me. I live in this practice box, I am local traffic and my phone lit up like a Christmas tree to make sure I was still alive when this happened. We can argue all we like about the ADS-B aspects of this but I think there’s more to it.

      First off what makes this a great piece of airspace for students also makes it potentially hazardous. There is literally a ring of airports that students and their instructors can use to practice including BJC, EIK, 18V, BDU, LMO along with FNL a couple minutes further north. The local 141 school is based at BJC and puts up a lot of sorties on any given day. Then you’ve got a skydiving business based at LMO, all of the 61 schools plus the local pilots. I’ve personally had the traffic at EIK get up to 10-12 aircraft in the pattern and then have someone drop in on the instrument approach. Fun times at an untowered field.

      Fortunately the CFIs are generally pretty good about radio calls and reporting points. It really does help pilots to know where to look. Where the system seems to break down is getting those frequencies disseminated out to the local pilots *and* getting them to at least be listening. Post the practice boxes along with frequencies at every FBO and flight school. We all seem to respect the published aerobatic box; it’s not that big of a lift to mindful of the high intensity training area. As pilots in command, I believe it is incumbent upon all of us to use all of the tools available to ensure the safety of our flight. As for me, I do my best to avoid it during peak times. Also, the 141 school has a pretty obvious rhythm and take advantage of the lulls to go to BJC.

      Now if I can just get fellow pilots to understand the level of raptor activity along Lookout Road. There are multiple groupings of bald eagles and osperys that ride the thermals and the rolling hills.

  4. Any piece of electronic equipment can fail at any time. When not in contact with Tower or Center you may not know. I’ve had a Mode C transponder continue to pick up the interrogation pulses but not transmit. No idea until maintenance as I don’t fly in controlled airspace unless I must.

  5. Other than compliance, what’s the relevance of no ADS-B in this mishap…Sonex was apparently squawking 1200 so shouldn’t the 172 have been aware of the non-maneuvering Sonex via ADS-B “In”?

    They call it “See and avoid”, not “ADS-B and avoid”.

    For the record, I am equipped, ADS-B compliant, flying near multiple east coast Class B’s, and for other than area awareness of targets, my experience is that ADS-B can be a “See and avoid” distraction in close.

  6. I fly several different types of corporate aircraft and my RV8 and I don’t trust ADSB for anything other than maybe being advisory. Daily, we are called traffic, or actually see planes visually that are not displayed. They come and go, or show up on one system, but not the other. It’s definitely NOT ready to be used as the sole identifier of planes near you. In VMC we better all keep our eyes out of the cockpit.

  7. ADSB was bad policy. They should have waited until something more reliable and cheaper was available. At any rate, one has to suspect this accident may have been caused due to over reliance on technology.

    Avionics shops are STILL taking months to fill demand for avionics upgrades and when this demand dies off, many of the new techs they have trained will then have to find new jobs. Some of the shops will likely close. Last time the government created extra demand and then squashed it, we ended up losing most of our aircraft manufacturers.

    I’m not a conspiracy guy so it’s obvious to me that no conspiracy to destroy piston could be as successful as the constant disregard for it from our government.

  8. My impression was that ADS-B Out was NOT intended for VFR traffic separation, it was mandated for controllers to have better separation capability in and under controlled airspace. In this case the controllers did not have that added information for the planes that they were working at the time.

  9. I like ADS-B a lot, numerous times it’s given me early warning to monitor or to act to alleviate an upcoming potential conflict, and I always find it useful in monitoring the current & upcoming traffic situation.
    Still, it’s just one of the tools in the kit, sometimes very useful and sometimes superfluous, and it’s purely speculative to assume its absence contributed in any way to this accident.
    The C-172 reportedly did have ADS-B “in” equipment, which if within range of a ground station we can speculate may have been displaying the Sonex as a basic 1200-code target. But we can also speculate the C-172 occupants were following the oft-repeated admonition to keep eyes out rather than including the display in their scan.
    Bottom line, unfortunately, is that accidents happen.

  10. A couple thoughts, ok arguments, on the usefulness and required-ness of ADS-B in this area. At a given time there are literally dozens of aircraft using the vortex of airspace between gnd and 2,500 AGL in a narrow band sandwiched between/under/adjacent mountains and class bravo. There are so many aircraft in the area that CFI’s/students will routinely cold-call other aircraft on the practice area freq that are near or appear to be conflicting. IE:

    Aircraft 1: “N12345, this is bugsmasher N67890 doing steep turns over the union res, we’ll be remaining at or above 7,500”
    Aircraft 2: “oh ok, N12345 will stay below 7,000 maneuvering and is looking for the traffic”

    If all 2-dozen aircraft to continually self-announced positions the practice frequency would be a non-stop garbled stream of “…err-POP-screetch-over the-BLOCKED!-mmm-7,500-please advise…”. What works over the fields of kansas does not work here. But yes, we’re still looking outside.

    Had this accident occurred between 2 aircraft that both had ADSB-in/out (and it easily could have), it would have been a sad failure of see-and-avoid. That it actually occurred between 2 aircraft, 1 of which had ADSB-in/out (the 172), and 1 of which did not (Sonex) where it was required to be broadcasting it’s position, sure makes this seem like an accident of negligence. The ADSB-in/out status of each aircraft is presented factually in the NTSB report.

    On the 172 still getting a primary 1200 target, not so fast. Yes, the location of the Sonex could be computed by ATC secondary radar, but the Sonex likely would be advertising itself as 1090ES ADS-B out since it had been in the past, and the 172 that says it has 1090ES ADS-B in, thus the FAA ground station would decide it doesn’t need to relay the position via TIS-B. No relay via TIS-B, no position to the 172.

    • “….the Sonex likely would be advertising itself as 1090ES ADS-B out since it had been in the past”
      The report says the Sonex was not broadcasting ADS data, and in fact they seem to believe it is probably the aircraft that had made several previous ‘illegal’ flights from Platte Valley without ADS-B. If, as elsewhere reported, the Sonex was utilizing one of the add-on 978 UAT devices for ADS-B, what would be seen was only its non-ADS transponder emitting basic transponder squawks.
      Also, I don’t think the FAA ground facilities make the kind of “decisions” about relaying or not relaying data that you describe.

  11. So, does this ADS-B warn pilots about other aircraft? I’ve heard of TCAS, but there are the old, reliable Mark One Eyeballs, and traffic calls that worked fairly well. If planes are colliding despite all these gizmos, maybe pilots should just learn how to scan better.

  12. In Australia ADSB is used by our air traffic control provider to cheap out on providing ground radars. Radar coverage is difficult as much of Australia is very sparsely populated and only good for strip mining, storage of nuclear waste and keeping the coasts apart.
    For the last 15 years sailplane pilots have been using a short range traffic warning system called FLARM. It helps against high speed near head on targets in the European Alps. Two sailplanes head on at 90 to 100 KIAS each is a more difficult problem than two B737’s head on at FL350.
    However it is nowhere near 100% effective. I know of several mid airs where both gliders had working FLARMs. In one case the units were warning of imminent collision, the pilots failed to see each other and at the last moment one turned – straight into the collision. Both managed to land safely in that one in Austria.
    Keep your head up, swivelling and eyes outside the cockpit. Seeing other traffic is an acquired skill.