The University of North Dakota and AOPA’s Air Safety Institute is performing a study of the use of the circular traffic pattern at general aviation airports. This type of pattern has been in long use by the U.S. military, with the Air Force and Navy using it as the emergency approach pattern and the Navy using it as the pattern of choice…at least since the British pioneered its use to get the F-4U aboard ship. I’ve flown the pattern as both a pilot and a RIO and use it today when flying simulated engine out approaches in my Light Sport Flight Design CTSW. I also work as a part-time safety analyst for the Flight Safety Office at Jonson Space Center, so I‘m content to wait for the study’s results and seeing their recommendations before formulating aa position. What I’m going to do here is detail some caveats centering around the Navy’s operating environment that affect its use and how that translates into the environment at a non-towered airport. Hopefully, the students conducting the study have some ex-Naval Aviators and USAF pilots at their disposal; not sure if the Army uses it, but if they do, then some insight from some Army pilots cold be helpful as well.
The Navy’s primary use of the pattern is to safely get aircraft aboard ship. It provides enhanced visibility of the landing environment (i.e., the ship and its position) and allows for smaller, more gradual, and continuous adjustments of your position to arrive on a final approach with consistency, something critical to the tight requirements needed to get aboard. Crews can and do use altitude gouges to judge glideslope at the 90 degree degree “to go” turn point (450 ft AGL) from downwind pattern altitudes in the same basic range as general aviation patterns (slightly lower than most actually; the F-14 NATOPS pattern was at 600 feet AGL). The pattern is intended to provide a stabilized approach beginning at the downwind abeam point. The aircraft hits that target “on speed” (green chevron on the AOA indicator, 15 units Angle of Attack for the Tomcat) and in the final landing configuration. That is gear down, flaps down, speedbrakes out (if applicable); no other major changes in aircraft configuration are made after that point since any changes in aircraft configuration can cause a major upset to an otherwise stabilized approach. Variables for the Navy pilot to deal with are therefore narrowed to controlling altitude and angle of attack and judging the rollout onto final (which will be slightly to the right of the ship’s wake to line up with the angled deck), followed by “Meatball; Lineup: Angle of Attack” until touchdown or bolter. The aircraft’s “locked down” configuration MUST be taken into account when discussing the stability and precision of the circular approach and before applying it to general aviation where that is often NOT the case. The FAA Flying Handbook instructs pilots not to go to full flaps until established on final and some preceding amount of flaps are applied sometime after the downwind abeam point, not ahead of it. While this is to give you the best glide possible in case of an engine out, it still means you’re going to make one of the most significant configuration changes you can make while also trying to get into an airspeed and descent rate stabilized approach. While the impact is more a function of the aircraft being flown than the type of pattern, but understanding the impact of configuration changes is a necessary part of evaluating the overall use of the circular approach and its for stability. You could decide to put the airplane in its final config and then count on the power being there as the Navy does and get all the benefit; but it’s unlikely that would be the case, even if the probabilities were to tell you that protecting for an engine out in the pattern might not be a good trade considering the safety gains of approach stability. This must be considered by the team conducting the study.
Likewise, the team needs to consider the fact that few Naval aviation operations take place in a nontowered environment. The closest thing to it are operations at Navy Outlying Fields (NOLF) used primarily for pattern training and that often have someone on duty and on the radios. While they are primarily there to make sure no one lands gear up, they also act as a traffic advisory service. Operations at other Navy airfields (and some NOLF’s and aux fields) are run by Navy air traffic control towers; aboard ship. the Air Boss and his staff take on the roll of an ATC tower. This significantly limits the opportunity for traffic conflicts due to someone making an unexpected/unannounced straight in or unorthodox pattern entry. When applying the circular pattern to nontowered genreal aviation operations, then, this means a very big question is, for the pilot in the pattern as well as anyone approaching the pattern, whether it introduces more risk to “see and avoid” than the rectangular pattern does.
For pilot in the pattern, since the transitions to each leg are performed in a constant turn, visibility of incoming traffic will be directly affected by whether the aircraft is high wing or low and the amount of bank used. Belly checks (rolling wing down in the direction of possible incoming threat…uh….traffic) may be employed to look for traffic blocked by the upturned wing; and, if used, become a factor that can destabilize the approach. (Scanning for someone on final approaching from the outside is done by just turning your head in a rectangular pattern.) This can be mitigated by using shallower angles of bank, which would be more necessary in a low or mid wing than a high but can mitigate the issue. Of course, the shallower the bank, the more stretched out from the runway the pattern becomes; but my guess is it would probably still be significantly less than the stretched out rectangular patterns I see too often at nontowered fields. For the pilot approaching the pattern, the additional turning of the aircraft in the pattern may them a bit easier to spot; in a rectangular pattern, there are large portions of it where the airplanes in the pattern may be climbing or descending but are wings level and not the easiest to spot.
These are things I expect the study to evaluate. Personally, I like the circular pattern; and as I’ve said, I will often fly it when performing simulated engine out approaches in my CTSW. I have also demonstrated it to students and friends who are curious about how the Navy does things. I don’t tend to use it when flying a Remos GX; its higher approach speed and less effective flaps make flying a rectangular pattern a more comfortable thing to do and what I need to teach my students to do. While I’m content to wait and see what the study arrives at, with the investment the community has in both training and operations in the rectangular pattern, I think it’s going to be a “hard sell” to move us to a circular pattern. There must be a very significant benefit not otherwise achievable to make it happen. I also think there are bigger fish to fry; the factors that drive loss of control in the pattern aren’t things that this protocol are going to affect. The collision risk may be another story; but it seems to me that could go either way. If we were to switch to a circular pattern, you could probably expect accident statistics to initially get worse until pilots got trained and comfortable with the new way of doing business.
No matter what pattern we ultimately fly, good headwork, situational awareness, and skill are what we need to determine whether flying on any particular day goes well or goes bad. When those things fail, all you’ve got left is a little luck. Hopefully, it goes your way…