Minneapolis Center controllers handed Stancie and me off to the temporary control tower at Tarkio, Missouri, with a clearance to fly a visual approach. We, and many dozens of other pilots, were arriving at Tarkio for the annual EAA Chapter 1405 Wing Nuts Flying Circus.
The Wing Nuts show is a little different, no, make that a lot different, than a normal EAA chapter fly-in. At Tarkio the stealth bomber B-2 flew over the runway so we could all see that exotic boomerang shape. Two FA-18s flew very long and impressive performances. And how many other local air shows have Sean Tucker performing?
The reason the Wing Nuts show is so well attended by pilots and performers is because Tarkio is the home airport of Missouri Congressman Sam Graves. Congressman Graves is on the Small Business Committee and the House Transportation Committee, both groups are crucial to all of aviation. And Congressman Graves is an avid aviator flying all sorts of airplanes including the T-6, Stearman, and other antiques and classics. Congressman Graves supports aviation, and we in aviation support him, and that makes the Wing Nuts show the biggest “little” air show in the country.
Because of the huge popularity of the fly-in at the single runway Tarkio airport a temporary control tower is wheeled in. Putting a tower at a normally non-controlled airport, and then flooding the airport with traffic, started me thinking about what controllers in a control tower really control.
The short answer is that the tower controls the runway. The primary function of the tower – local control in formal ATC speak – is to separate aircraft using the active runways. Controlling the airspace around the runway is a different situation.
The FAA has a very specific set of rules of how aircraft on an active runway must be separated to prevent collisions, and it is the job of the tower to enforce those rules. The most fundamental rule is that only one aircraft can be using the runway at the same time, so it’s the tower controller’s job to make sure the runway is going to be clear before approving pilots to land, take off, or cross the active runway.
Keeping airplanes apart on the runway is obvious, and makes sense. But to maximize use of a runway without compromising safety, tower controllers can issue clearance to one pilot to land if another is still on the runway but is rolling for takeoff. Or a landing clearance can be issued if the aircraft ahead is down safely and rolling out to clear the runway before the other lands. And in some circumstances on long runways pilots of airplanes of lower performance and less runway requirement can be cleared to land if the landing airplane ahead is far enough down the runway.
What a tower controller does to separate airplanes in the air around the airport is less clear. Even though we call the airspace around an airport with an operating control tower “controlled airspace,” the fact is that if conditions are VFR it is up to each pilot to see and avoid other traffic. That also goes for pilots still flying on an IFR clearance as we were when arriving at Tarkio.
Tower controllers do their best to point out known traffic to other pilots in the area. They have full authority to issue directions such as “follow the Cherokee on left downwind.” They can also clear pilots to enter the traffic pattern at a specific location, and that is a clearance we are obligated to fly.
Tower controllers can help establish safe separation for airplanes in the air by issuing clearances such as, “I’ll call your turn to base,” when they can see an airplane a pilot flying downwind doesn’t. The controllers can also tell pilots to fly a 360 if they see spacing on final is not sufficient, or they can request pilots to fly a minimum safe airspeed.
Though tower controllers are doing their best to help pilots separate themselves in the airspace around the runway, they are not “controlling,” or “separating” traffic in the same way that happens when we fly under positive control such as while in the clouds or above 18,000 feet.
When we fly under positive control we are separated from other controlled airplanes by maintaining an assigned altitude, and assigned course or heading. Pilots cannot deviate from those ATC clearances without declaring an emergency. Controllers use radar identification and procedures – the assigned course and altitude – to keep airplanes under positive control safely apart. And the system works. There hasn’t been a collision between two aircraft under positive control in decades.
At many airports tower controllers now have a radar display that supplements their visual observations and they can give pilots traffic advisories. Those radar advisories are a huge help, but are still not positive separation in the formal sense. The advisories are intended to help us see the other airplane so that we can then establish our own visual separation.
But at Tarkio on Saturday it was back to the basics of a “tower-controlled” airport where the controller did his best to see airplanes entering the pattern and instruct pilots to fall in behind airplanes he could see, but in the end the only positive clearances he could issue were to actually use the runway.
Even though I was still flying on an IFR clearance my duties to separate myself from the many other airplanes arriving was no different. The tower cleared us to enter a right downwind for Runway 36, even though the wind was building from due south. As we flew our clearance to enter the pattern the pilot of a T-6 – correctly so – refused the clearance to land on Runway 36 because the south wind was now approaching 10 knots. That’s a lot of tailwind for any airplane, and too much for any careful pilot of a heavy taildragger, so the T-6 pilot was absolutely correct to insist on using Runway 18.
The tower announced a runway change, so I rolled into a tight right turn to be on left downwind and found myself ready for a turn to base about the same time the tower controller saw me and cleared me to land No. 2 behind a Cessna on final.
The airspace around Tarkio seemed to anything but controlled as pilots were announcing their arrival from all directions and at a variety of altitudes and airspeeds. But guys in the temporary tower sorted airplanes out as they neared the runway and I didn’t see, or hear of, any close calls. The tower control system works, but we pilots need to remember that until we get close to the runway, maintaining safe separation is still our job.