ADS-B hockey puck
4 min read

Until recently, collisions between aircraft were rare, supposedly because pilots used See and Avoid.

But now ADS-B information displayed in our cockpit on the iPad reveals that this explanation just wasn’t correct. There were hardly any collisions because the odds of two aircraft meeting in the air were next to zero, due to the small volume taken up by two aircraft and the comparatively huge volume of available airspace.

But “next to zero” does not mean “zero,” as we found out during a recent trip, where in two instances, on the same day, we were mighty close to a midair collision.

So how did we avoid these potential collisions? We saw those airplanes on our iPad, since we now have both ADS-B In and ADS-B Out, and thus are continuously served with the location and speed of all aircraft within a so-called hockey puck surrounding our aircraft. It has a diameter of 30 miles and extends above and below us for 3,500 ft.

The ADS-B systems sends to us not just information about aircraft that also broadcast ADS-B Out, but for any aircraft that has a transponder.

ADS-B uplink

ADS-B is supposed to uplink targets that have transponders but not ADS-B Out.

The diagram at right shows how data of the latter aircraft are captured and included in the ADS-B system. The little red/white plane labeled “UAT” would be our aircraft receiving the information about the non-equipped aircraft.

First event

The first case happened at the Lee’s Summit airport in Kansas City. We had stopped for refueling on a trip from Ankeny, Iowa, to Dallas.

Winds were from the south, so for the departure we selected Runway 18 and continued the initial climb with heading 180.

We had hardly left the ground when a pilot asked on the aircraft traffic frequency, “Anybody in the pattern at Lee’s Summit?” No call sign, no position report, nothing, just that question.

Since we were neither in the pattern nor intended to enter the pattern, we did not respond, but were puzzled about this unorthodox way of inquiring about activity at the airport.

Then we glanced at the iPad. An aircraft was approaching the airport from the south, flying smack against departing traffic.

The pilot was flying approximately at pattern altitude, at the time was about two miles from the airport and in perfect position to collide with departing traffic.

Now what?

As we grasped the severity of the situation, it took a few seconds to anticipate what the pilot of the oncoming aircraft might do next, and come up with an avoidance strategy.

Our best guess was that the pilot would continue straight ahead. So for avoidance we made a sharp turn to the right, with the idea that we would be able to see the aircraft if we ever came close.

Checking with the display of the iPad, we saw that the pilot did continue straight ahead as anticipated, and that we were in the clear due to our turn.

A bit later, the pilot announced that this was a helicopter intending to land at the airport.

Second event

The second situation was just as nasty.

We were in Oklahoma, maybe 30 miles north of Denton. We scanned the iPad periodically, looking for other traffic converging on us.

There was one plane catching up to us, at the same altitude, but now and then climbing and descending a bit. Apparently a fun flight.

ADS-B hockey puck

You’ll see everyone inside the hockey puck, right?

We clicked on the plane’s icon and saw that the plane was doing 131 kts, much faster than our 90 kts. So this plane would catch up rather soon.

Indeed, it almost looked as if the plane were aiming for us, a disconcerting thought. Of course, we saw nothing outside since the plane was behind us.

Now what?

Given the plane’s horsing around, but more or less staying at our altitude, we decide to climb sharply and thus get out of the way.

Within a minute we were substantially higher, and when the pilot on the fun trip caught up to us, we were more than 500 ft higher.

What’s there to learn?

First, ADS-B reveals that the old strategy of See and Avoid is simply not sufficient to avoid collisions.

Yes, the probability of a collision is small, but that event does happen. Has done so at our Aero Country airport roughly once every ten years.

Second, even if you live in a location where ADS-B Out is not mandated, it is a smart idea to install it. If you don’t have ADS-B In, that’s needed, too. And, the sooner you do, the better the chance that you will not become a contributing data entry of mid-air collision reports.

Klaus Truemper
Latest posts by Klaus Truemper (see all)
16 replies
  1. Clayton Hammond
    Clayton Hammond says:

    I would contend that as departing traffic you were indeed part of the Lee’s Summit pattern. And more specifically your choice to fly outbound on the departure runway heading put you on “an extended upwind for Runway 18, departing to the south, runway heading”. An analogy to consider is a tower controller at a Class D field: Once an aircraft taking off clears the airport fence outbound, is he forgotten? No. He is still a target and threat for other aircraft the controller is potentially working within his airspace boundary. The same should apply in an un-controlled sense with regards to non-towered fields as well. If you are within a couple miles of the un-controlled airport, you are within the bounds of that airports traffic pattern. That traffic pattern should be considered an airspace boundary in this sense. Its arbitrary and subjective…say within two miles and surface to 1500 feet. YMMV… But if you are in it, whether coming or going, then you are a part of the action.

    An uncontrolled airport means too that the runway in use is ultimately determined by the individual Pilot In Command. You may be outbound on the “off-side” of the runway you just used, but that does not mean you aren’t potentially in the path of other traffic making for the field inbound.

    My opinion, but See And Avoid still has its place, most especially within the relative tight confines of a traffic pattern.

  2. Klaus Truemper
    Klaus Truemper says:

    Yes, you are right. It’s just that the off-hand question”Anybody in the pattern?” surprised and shocked me, and I turned first to the iPad to see whether it was showing the aircraft. It did, on a direct collision course. So instead of broadcasting my position and so on, as you have suggested, I focused on an evasive maneuver. Maybe not the best immediate reaction, but the off-hand terminology of the pilot scared me enough into that action.

    The short article is not meant to say that See and Avoid is no longer needed. Still needed just as much as before. But now, as ADS-B information comes in, I realize time and again, how close other airplanes sometimes are to mine, without any possibility that I could see them. I have a low-wing plane and cannot see what is immediately below me. On recent excursions it has happened more than once that an airplane was below me and climbing. Now with ADS-B I can respond to this with appropriate reaction.

    Lastly, I appreciate the time you have taken to analyze the situation and write down important points. After all, flying is a learning experience, no matter how many hours have already been recorded in the logbook.

  3. Al
    Al says:

    Thanks for this important article and the discussion.
    Did you announce your departure on the CTAF?
    Would it make sense to turn crosswind after departure, and turn back to runway heading only with a clear lateral offset from the glidepath, as a standard procedure?

    • Wes Hoy
      Wes Hoy says:

      I hear that call just about every time I fly and I don’t like it. First off, I would have announced my departure and direction of flight, then I would have transmitted something like: “Pilot calling Podunk County….say position and altitude…Cherokee 123J just departed runway xx climbing through 500″….It is not my most disliked non-towered airport habit, which is a straight-in without entering the pattern…

  4. Klaus Truemper
    Klaus Truemper says:

    Yes, I did announce the departure, with details of runway used and direction of flight after takeoff. That’s another reason why I was baffled by the question “Anybody in the pattern?” It made me think that I needed to get away from the other aircraft as fast as possible.

    You pose an interesting question about the departure route.

    Sorry, I have no good response to your proposal. As for me, I do the following. As soon as I am 400 ft AGL, I depart in the announced direction and continue with a modest climb rate. The goal is to get out of the airport traffic and, while doing so, stay significantly below pattern altitude.

    There is one important exception to this low-level departure.

    Suppose I take off south on runway 18 and departure will be north. On the advice of a very experienced pilot, I then continue south and climb to 400 ft below the pattern altitude before I turn left to go north. Continuing with a steep ascent, by the time I am abeam the south end of the runway, I am already significantly above pattern altitude. Hence, any traffic entering left downwind for runway 18 will be below me. This has served me well.

    Another advice, from the same pilot, is to climb in a slightly weaving pattern so that I get different forward views all the time and there is no blind spot. This has served me well, too.

    But in addition to all that, there is now ADS-B. And that’s why I wrote up the comments in the first place, to motivate pilots to install the equipment even if not legally required for their type of flying.

  5. Enderson Rafael
    Enderson Rafael says:

    Jetez la premiere pierre who never lost its breath flying without tcas, right? I had at least two close calls while flying light acft in Florida, and once, over Georgia, we had TCAS and spotted a Cirrus coming from below us, climbing fast, and he was not talking to atc. We turned left just in time to see it passing up. It would have been a silly dead for sure. Hopefully the ADSB rule will increase the safety of our skies way more than we can antecipate.

  6. Jack Cole
    Jack Cole says:

    An “anybody in the pattern” call is pretty common at non-towered airports.
    Even if the call is insufficient, you can increase safety by contributing information, eliciting more from the caller.

    You were puzzled by the call since you just announcement your departure.
    Maybe the other pilot selected the frequency after you announced; wasn’t paying attention when you announced; or didn’t think your transmission concerned Lee.
    Just skip past this, and respond.

    You were in the pattern if you “hardly left the ground”, but even clear of the pattern you should respond while still on frequency.

    Instead of “anticipating” the other flight direction, ask.

    “Aircraft calling Lee, [your tailnumber] just departed runway nn Lee to the [direction], now x miles out at [altitude] and are unaware of any other traffic. Say your position.”

    In a perfect world everyone meets all requirements for IFR and for VFR ADS-B.
    Lucky for you this flight had ADS-B Out. Others won’t.

    Your response could increase the safety of caller’s passengers, other unknown flights (no ADS-B), people on the ground, despite the poor call and poor quality pilot (student, poorly-trained, inexperienced, all of these).

    Never, ever pass up an opportunity to expand a poor communication into a life-saving one.

    “See and avoid”, ADS-B, and various quality pilots have strengths and weaknesses.

    Pilots must be aware of these, his or her own failings, and compensate, adjust on a regular basis.

  7. Morrie Caudill
    Morrie Caudill says:

    I’m one of those non-ADS-B’ers and I’m afraid the digital cockpit will cause more head down flying. Uncontroled airports require position reporting, on the correct frequency, to protect everyone in the pattern. And, remember there are some of us out there without radios also. Heads up.

    • Robert
      Robert says:

      I think everyone who can install it should have ADS-B Out. That way those of us with ADS-B In have an easier time spotting those that are not talking and avoid them. It is a lot easier (tho still not easy) to pick out another plane when you have better knowledge of where to look. As for those without radios – that seems to me like driving around at night with your lights out, and expecting the rest of us to avoid you.

      Especially in the northeast – there is so much traffic up here. Flying into Plymouth a couple of weeks ago, a CAP flight off to the southeast of the pattern kept announcing, there were 2 of us arriving from the northwest, 2 helicopters nearby, and someone faster than all of us on downwind already as we were getting near. I saw everyone who had ADS-B, never did see the CAP flight who I suspect was not ADS-B equipped. The helicopters were right traffic, we were left, so that just really left the CAP flight as an unspotted danger.

  8. Marc Rodstein
    Marc Rodstein says:

    Maybe we should anticipate and be ready for “anybody in the pattern” but it is poor form and not helpful. A pilot should always announce his position on the first transmission so that other traffic will know where to look for him or her.

    That said, I agree with the original poster that ADSB traffic is a game changer. I am constantly seeing traffic on the iPad that I never would have spotted visually. Even knowing via ADSB just where to look, sometimes I still fail to see that traffic. It is scary to realize how much traffic is out there that we cannot see.

  9. Bruce Webbon
    Bruce Webbon says:

    In the days before ADS-B about 10 years ago, I had a very near collision at 8,500 ft over the central valley of California.

    I was in Travis AFB North airspace nearly to the point where they would hand me off to Oakland Center. I had flight following and was commuting home after a week at work at NASA Ames Research Center in the SF bay area. The Travis North controller gave me an alert of overtaking traffic at my altitude and at the same time he alerted the other aircraft, a C210. He then said the key words, “No factor” as he handed me off to Oakland so I relaxed and apparently the 210 pilot did the same.

    I had the Oakland frequency already dialed in and was about to check in when I saw a flash of movement on the right in my peripheral vision. It was the 210, not more than 100 ft away at my altitude and converging. I could easily see the pilot looking inside probably at his radio. He apparently saw me about the same time and started to turn but it was too late. He crossed right in front of me so close that I went through a very strong wake.

    We both immediately started babbling to the Oakland controller. She was very confused and concerned because she thought we had just collided. We had merged on her radar screen. She apparently handed off all the rest of her traffic to another controller because we spent the next 20 minutes talking with her trying to figure out how it had happened.

    We were both directed to call an FAA number after landing and make a report. The FAA person also directed me to call the shift supervisor at Travis. I did that and the supervisor, a sergeant, was very crabby and defensive trying to defend his controller. I also filed a NASA report as did the other pilot. I eventually talked with the folks at the ASRS program since I knew the director. I was told that there was an investigation by both the military and the FAA but I never heard anything about what they found.

    In my personal opinion it was very clearly the fault of the Travis controller. I believe that he thought our tracks were parallel, not converging, and he didn’t pay attention after he directed us to contact Oakland. It was just total luck that we didn’t collide. Fate may be the hunter but she missed me that day.

    My conclusion was that doo-doo happens but I would do my best to make myself as small a target for the hunter as possible. I equipped my C182 with ADS-B out several years ago when the FAA first started their rebate program. I live way out in the boonies of SE Oregon (KLKV) so the only traffic I see on my ipad most of the time is airliners cruising 35,000 ft overhead. However, whenever I fly into the congested bay area or even worse the LA basin I am amazed at all of the traffic that I usually can’t see.

    Sorry for the long monolog but your story brought back some old memories.

  10. Joel Godston
    Joel Godston says:

    When I was being checked out to pilot a SAC B-47 in Wichita, Kansas, just after I received my wings in US Air Force pilot training (class of 57H), we were doing a low approach wuth many, MANY aircraft in the area. So, you had to not only fly your airplane. but be looking for ALL the other aircraft around you. On one approach, I identified a small single engine airplane (I think it was Cessna 172) VERY close. The A/C said he did not see it, and told me to take control of the B-47…. which I did, and we cleared the aircraft…reported the incident.. and continued our training flight with no other ‘close calls’… Yes, sometimes flying can be exciting! .. and I have had many during my 50+ years of flying!

  11. tom Connor
    tom Connor says:

    “Anybody in the pattern at Lee’s Summit?”

    You should have responded with your position report, not look down at the iPad. The other guy might have had distractions or an emergency. In my experience, choppers don’t fly patterns much, nor are they required to. Heck, in reality, there are a few AIM recommendations for fixed wing aircraft and hundreds of ways to do it, all legal.

    Read Pelican’s Perch #30 about traffic pattern nazis. John Deakin explains his approach to flying traffic patterns at non-towered airports, which involves hard-to-legislate concepts like common sense and courtesy.

  12. Klaus Truemper
    Klaus Truemper says:

    In the olden days, I would have agreed: Make a position report and wait for the reaction by the other pilot. But with ADS-B, I first look and see if there is an immediate danger. I can do that with one glance at the Garmin Pilot display. And if there is an immediate danger, I react to that danger first: Diving, climbing, sharp turns, whatever it takes. That’s what happened at Lee’s Summit. With one glance at the iPad, I saw the aircraft, and my first reacting was to get out of the way. Did that that by a sharp turn to the right and reducing the climb rate, all intended to stay below the other aircraft and give me a view of the aircraft. My plane has 360 deg visibility and as low-wing aircraft let’s me see everything above me.

    Yes, and at that point I could have made a position report. What would I have said? “Making a sharp turn west” etc. ? But regardless, next time I will do so.

    Agree with another comment: In a busy airspace, a radio is a must for safe operation. There are low-cost portable radios that will suffice.

    There may be a misconception about ADS-B. The ADS-B system doesn’t just capture aircraft that broadcast ADS-B Out, but also all transponder-equipped aircraft that do not have ADS-B Out. Of course, there is less information about the latter aircraft, but they do show up on ADS-B In if, and this is an important if, you have ADS-B Out. See the next paragraph. For example, my home airport is under the DFW class B space and thus requires all aircraft to have a transponder. So almost all aircraft show on my ADS-B In. Yes, the folks without electrical system are exempt, so ADS-B does not supply perfect information. But it is a very important add-on to See and Avoid.

    Now if you have ADS-B In but not ADS-B Out, the information about aircraft without ADS-B Out but with transponder will not show up on your ADS-B In unless you are in the hockey puck of coverage of an aircraft that does have ADS-B Out. And even then, if you are at the edge of that hockey puck, you may not see all aircraft relevant for you. That makes reliance on ADS-B In when you do not have ADS-B Out quite dangerous. Bottom line: ADS-B Out coupled with ADS-B In is a crucial way to enhance safety.

    Lastly, it is enlightening to read the various comments. I write a blog about small aircraft maintenance and various issues connected with low-level flying.
    It’s popular with the Rotax crowd.

    The post appeared there first about eight months ago, and did not produce any comments. And here there are lots of comments and ideas! Which proves that Air Facts is a terrific program to help pilots.

  13. Tom Brusehaver
    Tom Brusehaver says:

    The first time I flew a C-172 with a G-1000, it was information overload. I was flying out of ADS (Addison TX) under the DFW class B, so the screen was full of aircraft.

    Flying straight and level, watching the screen is good for traffic awareness, but if you are flying at 3000ft, do you care about the jet at 10000ft? Probably not, you may be able to see them anyway. Which way are they going? How fast are they?

    It takes too long for your mind to process the data on the screen. Most of the aircraft in the class B airspace are not going to be an issue, plus you have people on the ground watching.

    The place where they ADS-B in will be the most useful is at a busy non-towered airport that you are are trying to land at. While you are looking at the screen at pattern altitude to see if that Cherokee is at 8000ft or 3000ft, a nordo cub just flew under you at 900ft you didn’t see it.

    See and avoid it primary for safety, ADS-B in is a tool to help augment it.


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