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.
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.
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.
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.
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.
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.
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.