Surviving the merge: how to avoid a mid-air collision

The AOPA Air Safety Institute’s Spring 2018 safety seminar tour is titled “Collision Course: Avoiding Airborne Traffic” and covers how to avoid mid-air collisions. Part of the seminar focuses on the specifics of FAR 91.113 Right of Way (RoW) Rules, the various conditions where they are likely to be a factor, and the appropriate actions pilots should take in any given situation.

After presenting it at more than a dozen locations around the country, I’d like to highlight some observations and issues that came up during our discussions. First, we’ll review what the regulations say, then we’ll break them down and look at how they might be applied in specific scenarios.

FAR 91.113 Right-of-way rules: Except water operations

(a) Inapplicability. This section does not apply to the operation of an aircraft on water.

(b) General. When weather conditions permit, regardless of whether an operation is conducted under instrument flight rules or visual flight rules, vigilance shall be maintained by each person operating an aircraft so as to see and avoid other aircraft. When a rule of this section gives another aircraft the right-of-way, the pilot shall give way to that aircraft and may not pass over, under, or ahead of it unless well clear.

(c) In distress. An aircraft in distress has the right-of-way over all other air traffic.

(d) Converging. When aircraft of the same category are converging at approximately the same altitude (except head-on, or nearly so), the aircraft to the other’s right has the right-of-way. If the aircraft are of different categories

(1) A balloon has the right-of-way over any other category of aircraft;

(2) A glider has the right-of-way over an airship, powered parachute, weight-shift-control aircraft, airplane, or rotorcraft.

(3) An airship has the right-of-way over a powered parachute, weight-shift-control aircraft, airplane, or rotorcraft.

However, an aircraft towing or refueling other aircraft has the right-of-way over all other engine-driven aircraft.

(e) Approaching head-on. When aircraft are approaching each other head-on, or nearly so, each pilot of each aircraft shall alter course to the right.

(f) Overtaking. Each aircraft that is being overtaken has the right-of-way and each pilot of an overtaking aircraft shall alter course to the right to pass well clear.

(g) Landing. Aircraft, while on final approach to land or while landing, have the right-of-way over other aircraft in flight or operating on the surface, except that they shall not take advantage of this rule to force an aircraft off the runway surface which has already landed and is attempting to make way for an aircraft on final approach. When two or more aircraft are approaching an airport for the purpose of landing, the aircraft at the lower altitude has the right-of-way, but it shall not take advantage of this rule to cut in front of another which is on final approach to land or to overtake that aircraft.

The Issues

Airplane out side window
That little dot can become another airplane very quickly.

FAR 91.113 lists different rules that apply when mixed categories of aircraft, certain operations, or aircraft with an emergency are involved. To keep it simple, we looked at situations involving two healthy single-engine airplanes. One thing to keep in mind, although 91.113(g) specifically addresses “Landing” scenarios, any of these situations could be encountered in the traffic pattern, which is where most mid-air collisions occur.

Most folks could recall the basic concepts of 91.113 without much prompting; however, I was a bit surprised at how long it took some of them to figure out the correct answer to who had the RoW, as presented in a basic scenario. It also became clear that even though they knew the general content of the regs, they hadn’t considered what they would really do, with their airplane, in the event an airborne encounter actually required them to maneuver accordingly.

What Would You Do?

To induce a little stress, I conducted an experiment by asking them, “What would you do?” in case you’re startled by a pop-up, short-range, up-close-and-personal flight path conflict, and had to decide and act quickly to avoid a mid-air collision.

Another question I posed to everyone: How long are you going to wait for the other pilot to react and “give” you the RoW, assuming it is yours, according to 91.113? At some point, it doesn’t matter who has the legal RoW. You can only fly one airplane, and you may to move to avoid a collision, whether you have the RoW or not.

When it comes to maneuvering, I revert to the three axioms of dogfighting that served me well as a fighter pilot: “Maneuver in Relation to the Bandit;” “Lose Sight, Lose Fight;” and “Energy versus Nose Position.” Although the other aircraft flying around in the NAS aren’t “bandits,” they are potential threats, and the concepts are the same.

I’m not advocating that you try to fly your light single- or multi-engine airplane like a fighter. I’m also not trying to convince anyone that my tactics and techniques are the only options, but I do challenge pilots to consider what they would do if confronted with a situation that required immediate, aggressive, possibly violent, maneuvering to avoid a collision. Although you may have to maneuver aggressively, tempering that aggression so you don’t rip the wings off, or depart controlled flight, is difficult when the adrenalin is pumping.

The main goal is to not hit the other aircraft, or anything else in the process. It’s not to get anchored in a big Swirlin’ Hooley dogfight, break into an impromptu aerobatic display, or fly an unbriefed formation. My objective was to get them thinking about what they are able and willing to do in their airplane. It was NOT to scare them into never wanting to fly again.

Tactics, Techniques, and Procedures?

Never intentionally put yourself where you’ll lose sight of the other aircraft, at least before you know your flight paths are deconflicted. Ideally, don’t go where he’ll lose sight of you. If it comes down to requiring aggressive end-game maneuvering, he probably never saw you in the first place, and even your wing or belly “flash” might not get his attention.

ADS-B traffic
ADS-B traffic can help you spot potential conflicts before they become serious threats.

In no case do the regulations say you must maneuver in one “plane of motion” (POM); e.g., level flight. If possible, I’m always going to get out of the other aircraft’s POM by changing altitude and use vertical separation in addition to any course alteration that is required.

A lot of pilots said they would “ALWAYS go underneath” the other aircraft to avoid a mid-air. I’m just the opposite; I would not choose to go underneath the other guy unless I was forced to. More on this later.

A number of folks responded with, “Well, what if he does a (Fill in the Blank) maneuver?” My answer: Be ready with your own follow-on maneuver, just in case. These close encounters shouldn’t evolve into a multi-turn, slow-speed knife fight. They’re going to happen quickly and result in either a miss or a collision. If you’ve got to do several maneuvers to avoid the other plane… something unusual is going on.

The 60:1 Rule

According to Advisory Circular 90-48D, “Pilots’ Role in Collision Avoidance,” the average person takes 12.5 seconds to see an object, recognize it as an aircraft, become aware of a collision course, decide which way to turn, then react, and for the aircraft to respond. Hopefully, you’ll have that much time and distance available before impact.

The further out you can see another aircraft, the longer you’ll have to determine if there may be a RoW situation, and the more maneuvering options you’ll have in order to avoid a conflict. The further out you maneuver, the less of it you’ll actually have to do.

Conversely, the closer-in you pick up the conflict, the less time and distance you’ll have to resolve it, and the more violent any maneuvering, yours and/or theirs, might end up being. A 10-degree check turn at five miles can be done much more gracefully than a 90-degree turn inside .5 miles.

One benefit of having ADS-B In capability is seeing at least a more complete picture of what’s around you, even if it’s not a 100% accurate.

The Classic RoW Scenarios

The following five scenarios are ones we spent time discussing. In each case, where applicable, the GREEN plane has the RoW under 91.113.

1. Converging. “When aircraft of the same category are converging at approximately the same altitude (except head-on, or nearly so), the aircraft to the other’s right has the right-of-way.”

Mid-air scenario 1
The airplane to the right has the right of way.

In this first scenario, we discussed what you would do if you were in the Cessna and had the RoW but found yourself in an extremely close encounter with the non-maneuvering Cirrus. This is where a lot of folks said they would “ALWAYS go underneath.” Let’s think this through.

Simply unloading an airplane to less than one positive-G is very uncomfortable for a lot of folks, even if it’s a planned maneuver. If startled, aggressively shoving the stick/yoke forward, to avoid a collision, maybe all the way to the instrument panel, and perhaps hitting two negative-Gs or more, is something most pilots are just not programmed to deal with.

Unless you’re trained and/or used to doing it, your body’s instinctive, overpowering reaction is likely going to be to yank back immediately into positive-G territory. Depending on how violent your reaction is, you may find yourself pulling right back into the other plane’s flight path.

Remember that unloading the wing, especially with the plane’s nose pointed down, is going to result in an acceleration that will increase your closure rate and decrease the distance quicker.

Going underneath is also likely going to result in one or both of you losing sight. In our scenario, we’d have a worst-case combination of a high-wing Cessna, going under a low-wing Cirrus, effectively putting each other in the worst possible blind spot situation.

In reality, the same could be said for any combination of wing configurations; most low-wing planes still have solid cabin roofs that can block the view under the right circumstances. Most high-wing airplanes, with side-by-side seating configurations, still have opposite-side doors and solid floors that obstruct vision.

My plan: If possible, I’m going to go up; I’ll aggressively pull the stick/yoke back and I may also rip the throttle to idle, at least momentarily, depending on my energy level. I can quickly evaluate whether this positive-G maneuver is getting me out of his POM. It’s also going to decrease my airspeed quickly, while slowing my closure towards him. I’m cognizant of the potential to stall and I’ll avoid it.

If he didn’t see me before, perhaps my big “belly flash” will get his attention.

I’m also going to roll and pull towards his tail/6-o’clock, while endeavoring to keep him in sight. Pointing my “lift vector” behind his tail is the fastest way to spit him out going the opposite direction and increase our separation. At that point, I don’t really care what he does, because our flight paths are deconflicted, and we should be well clear of each other.

Never turn in a direction that will put you in front of, or converging with him, even if you do change altitude.

Despite all that, if you’ve got enough altitude and do opt to slide underneath, you’re probably not going to hit anything else. On the other hand, what if you’re in the pattern? Look at the illustration again: Imagine you’re on short final at a couple hundred feet AGL, and someone on a close-in base leg cuts in front of you; going underneath them, near the ground, might prove catastrophic. I’d hope your initial reaction instead would be to initiate a climb/go around.

2. Approaching head-on. “When aircraft are approaching each other head-on, or nearly so, each pilot of each aircraft shall alter course to the right.”

Mid-air scenario 2
Alter course to the right – for both airplanes.

In this scenario, how much “alter course to the right” is enough? And when can you get back on your original course? It’s up to you.

Regardless of how much course altering you do, the end result should be a left-to-left pass. You can also combine an altitude change with the course change, but, it’s critical that you pick each other up visually after maneuvering. If the other plane is not there, someone probably turned the wrong direction.

An informal audience poll concluded that the reason for the “alter course to the right” is because of how we drive our cars… in America, at least. Makes sense to me.

On the other hand, this is one scenario where some of us might be set up to fail in the first place. In a surprise, short-range situation, like a close-aboard, head-on pass, there’s potential for human nature and muscle memory to cause at least one of the planes to turn the wrong direction, resulting in an unintended game of “Chicken.” For some of us, it just takes more conscious thought to turn right, than it does to turn left.

Here’s my theory: The correct maneuver is a course change, or turn, to the right. Unfortunately, we fly in a left-turn-biased world. The standard traffic pattern is left hand turns. In a standard side-by-side seating configuration, the PIC usually flys from the left seat, with the left hand on the yoke. If told to execute a steep turn, in either direction, I think most pilots would choose a left-hand turn instead of a right-hand one. For me, it’s easier to “pull” it into a left-hand turn, than to “push” it into a right-hand one.

In a typical tandem-seat taildragger, the throttle is on the left side, and the right-hand palm is placed on the right side of the stick. Same phenomena in a turn; but in this case, it’s easier to “push” the stick into a left turn, than to “pull” it into a right turn. It’s also seems easier to slip to the left, aileron roll to the left… etc.

Everything about flying a U.S.-manufactured airplane (with a U.S.-manufactured engine) has a “left” component to it. Even though we’re constantly applying right rudder to compensate for the left-turning-tendencies inherent with our clock-wise spinning propellers, I think we’re still more inclined to turn left, especially in a panic. Think about it the next time you fly.

What are the chances of a head-on in the traffic pattern? It happens when pilots opting to use the runway of their choice are in conflict with someone else who thinks otherwise. I’ve experienced this situation many times at airports with recommended calm wind (which includes tailwinds up to 3 knots) runways. Both planes are landing (or taking off) on a “correct” runway; they just happen to be 180 degrees apart. Hopefully, someone abandons their approach early and initiates a go-around. Having “each aircraft shall alter course to the right” during landing roll out, is pretty tough to do on a 75-foot-wide runway.

3. Overtaking. “Each aircraft that is being overtaken has the right-of-way and each pilot of an overtaking aircraft shall alter course to the right to pass well clear.”

Mid-air scenario 3
Remember to pass well clear when you alter course to the right.

This is the only scenario where the FAA specifically re-stipulates “pass well clear.” I’d like to think we’re trying to pass well clear in all cases! What is FAA’s definition of “pass well clear?” There isn’t one: It’s up to your discretion and is very subjective.

There’s no requirement for the overtaking plane to stay at the same altitude and pass the other plane line abreast. If I’m the overtaker, I’ll combine lateral offset and an altitude change to ensure the other guy can’t turn into me. If possible, I’d like at least one turn diameter (his, not mine) of separation. If you don’t know how big his turn circle really is, I’d give him at least 5,000’. (If he holds a level, 30-degree bank turn at 120 knots, his turn diameter is about 4400’). That way, even if I lose sight and/or haven’t changed altitude, I should be safe if he turns into me.

The closer the overtaking aircraft is, and/or the faster the closure, the more aggressive the maneuvering will have to be. If you’re going really fast, and are surprised by your closure rate, you can always use maneuvering with increased G and/or a power reduction, to slow down, along with an altitude change.

The last time I was overtaken was in the traffic pattern, on downwind. Our wings overlapped, with his left wing going under my right wing. My reaction was to barrel roll to the left, while he continued straight ahead.

How many pilots randomly, let alone routinely, maneuver during flight so they can visually “Check Six” just to make sure the Red Baron isn’t closing in? After flying with ADS-B In, I’ll bet a few more do.

4. Landing.“Aircraft, while on final approach to land or while landing, have the right-of-way over other aircraft in flight or operating on the surface, except that they shall not take advantage of this rule to force an aircraft off the runway surface which has already landed and is attempting to make way for an aircraft on final approach.”

Mid-air scenario 4
The airplane on final has the right of way, but don’t abuse this privilege.

This first landing scenario tends to occur when an IFR aircraft shows up in the VFR pattern, or when any aircraft, IFR or VFR, opts to arrive using a straight-in approach.

IFR traffic do not have the RoW by virtue of just being on an IFR flight plan. Their RoW priority is dependent on how/where they fit into the flow with other traffic. Unless they’ve been monitoring CTAF on a second radio, IFR traffic may have precious little time to build an accurate traffic pattern picture after approach control clears them to contact the local advisory frequency.

An interesting twist to this scenario is when an aircraft reports established on an instrument approach/straight in, and specifically states their intentions are to do a “low approach.” A “low approach” is not a “landing,” which is the criteria that the RoW is established on. So, what to do? In this case, my informal poll revealed most folks already established in a rectangular VFR pattern are more likely to extend/adjust their pattern legs, to allow the straight-in traffic to execute whatever maneuver they choose to terminate their approach with.

This is also a case that highlights the danger inherent when not all the aircraft in the traffic pattern have radios, or have their lights on, even if they’re not required by FAR. It may be tough for someone on a close-in, but legal, base leg, to see traffic that’s on a 4- to 7-mile final approach, pointing directly at them, against an adverse background. I always assume there is someone else out there, even if they aren’t talking; I just don’t see them. It’s also critical that IFR aircraft switch to “VFR Speak” when they get on the CTAF. I may have no idea that the name of the final approach fix is SCENN, but I do know roughly where to look for you if you report a “5-mile straight-in, Runway 17.”

5. Landing. (Cont.) “When two or more aircraft are approaching an airport for the purpose of landing, the aircraft at the lower altitude has the right-of-way, but it shall not take advantage of this rule to cut in front of another which is on final approach to land or to overtake that aircraft.”

Mid-air scenario 5
This scenario usually happens when two aircraft with significantly different speeds approach at the same time.

Like the previous landing scenario, a “low approach” is not a “landing,” as compared to a touch-and-go, stop-and-go, full stop, or “the option.”

Conflicts here can result when two aircraft, with different size/speed/performance characteristics, and pilot techniques/preferences, are each flying a completely legal traffic pattern for the same runway, but of significantly different dimensions.

Here’s a summary of the FAA guidance that defines what the rectangular traffic pattern should look like:

  • 45-degree entry to downwind leg recommended (AIM & AFH)
  • Downwind leg spacing: ½ to 1 mile from landing runway (AFH)
  • Turn base leg @ 45-degree angle to approach end of runway (AFH)
  • Complete turn-to-final at least ¼ mile from runway (AIM)
  • Traffic Pattern Altitude: “1,000’ AGL recommendedunless established otherwise” (AIM); “usually 1,000’ AGL” (AFH).
  • Heavy and Turbine TPA @ 1,500’ AGL: FAR 91.129Class D airspace. (Plus C & B also.)

(Note: Traffic patterns are also discussed in AC 90-66B, Non-Towered Airport Flight Operations)

Let’s say two planes are beating up the pattern at a non-towered airport with Class G airspace. One is a high-performance, complex, retractable single, flying 120 knots on downwind leg with 1-mile runway spacing. He turns base when the runway is at 45-degrees and rolls out on a 1-mile final at or above 300’ AGL, to be at or above a 3-degree glide path. At the same time, a J-3 Cub, with no radio, flying 60 MPH, uses ½-mile downwind spacing, also turns base at 45-degrees, and rolls out on a ½-mile final at 150’ AGL on a 3-degree glide path. Or, he tightens up his base leg to roll out on a ¼-mile final and 75’ AGL to be on that same 3-degree glide path. Neither plane is breaking a regulation, or violating any guidance.

The only leg of the traffic pattern they have in common… is short final approach… where a lot of mid-airs occur. How many laps around the pattern will it take before their flight paths merge, especially if either one, or both, loses situational awareness?

A lot of small piston-powered airplane pilots, flying at a 1,000’ AGL TPA, think they are safe from conflict involving large or turbine-powered airplanes, because they “must enter the traffic pattern at an altitude of at least 1,500 feet above the elevation of the airport…” Read the regulations: Even though you might think they should be at that higher altitude, the regulatory requirement to be there doesn’t apply until you get to Class D airspace (FAR 91.129, Operations in Class D Airspace). That means they could be down there with you at 1,000’ AGL, at 250 knots… (unless your airport’s Class G airspace underlies a Class B shelf).

In any landing scenario, the potential for someone to be “startled” is pretty high. This is where the “always go underneath” reaction could prove fatal. Obviously, with any aggressive maneuvering at low altitude, you’ve got to maintain aircraft control, since you may be too low to recover.

Bottom Line

Being surprised, shocked, startled, with not a lot of time to evaluate all the options, yet still pick one and execute it, is an extremely unfortunate set of circumstances to find yourself in. Using solid, disciplined “see and avoid” visual scanning techniques, ADS-B In/Out and other technologies, plus available ATC services, are great ways to mitigate the threat of a mid-air, but you still have to be ready, willing and able to max perform your plane.

11 Comments

  • Excellent review. I always teach right-of-way doesn’t always work. You have no idea if the other aircraft sees you so do what ever will work. Changing altitude is quickest, turning toward the other’s tail allows you to keep him in sight.

  • Thanks a lot for the article Tom. This very topic has been in my mind a lot in recent years.

    Not all pilots display the same level of airmanship and proficiency.

    I have witnessed several close calls, some at fly-ins where I have seen sunday flyers barge into the traffic pattern, endangering others.

  • Tom, In my January 31, 2018, webinar for the Experimental Aircraft Association, I explained why it is rarely a good idea to bank as a collision avoidance maneuver, especially if there is very little time to do so. Banking aircraft create reports on the NTSB Index of Months where “minor” wingtips offered up as sacrificial parts in a collision cannot have their lost life mitigated by the aileron on the opposite wing. Dr. H. Paul Shuck had an earlier webinar about his January 30, 2016, accident where he survived in part because he did not waste time banking. He only pushed into a dive, leaving his wingtips too low (along with the rest of his airframe) to be cut off. My webinar is at https://video.eaa.org/detail/video/5724032078001/

    • I agree: Merely rolling into a bank, is not the best way to avoid a mid-air collision (unless you’re in the Thunderbirds, doing a head-on, knife-edge pass). The best option is to get out of the other guy’s
      POM (plane of motion).

  • Excellent article. I especially like the part about not waiting too long for the other plane to react when you believe you have the right of way. The rules only work when all the pilots in converging aircraft know they are in a situation where they must be applied. I ride motorcycles, and this axiom is crucial for that regime as well. A really excellent motorcycle instructor once told me there are a lot of riders in graveyards who had the right of way.

  • Thx for a good article from a good source. Prevention and not losing sight really are key.

    Another emphasis for why collision avoidance maneuvers should be large and obvious (e.g. belly or wing), is that small nibbles will have the other guy guessing what you’re doing to avoid collision and he may try the same thing.

    Nautical world handed down our rules and a factor in many of their collisions is waiting too long for avoidance and then using small, hard to observe course changes when in extremis.

    Additionally, and unfortunately, most GA pilots have never been taught how to aggressively move their aircraft in 3 dimensions without pulling of their wings or “smoothly rolling into a bank”. Canned 45 aob (steep?) turns and stalls are just not enough.

    • Good points:

      The BIG Factor, in the air (and on water), is do they see each other far enough out to avoid in extremis situations in the first place?

      And if only one sees the other—who sees who?

      The good news: Unlike with boating, there’s no FAA requirement for the “stand-on vessel” to maintain its course and speed, while relying on the “give-way vessel” to maneuver to keep clear.

      The bad news: Planes can’t blast air horns at each other, just in case!

      • Harder to hear the horns over the engine and my radar keeps blowing off the bridge!

        When we all should be up ctaf (realizing it’s never 100%) ctaf is another tool to (constructively) talk out the plan if there’s no immediate threat…or announce maneuvering intent when there is. It’s useful for more than rote position reports (or rental car arrangements with the FBO…ugh).

        Even when up ATC, and I know I’m the (vfr) conflict, I’ll volunteer my intent to ATC knowing that the other party will hear or get my intent relayed.

        Thanks again for a good briefing on an important topic.

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