Midair collisions are the primary hazard associated with flying at nontowered airports. Most midair collisions occur in clear weather within five miles of an airport and below 3,000 feet, which is where aircraft congregate. Most collisions occur on final approach, generally when a faster aircraft overtakes a slower one.
So I decided to research a bit about why this would be true. If every one is using the self announce frequency as they "should," every pilot should know the location of every airplane operating at that airport (whether or not they say "All traffic in the area please advise") and be able to avoid them! But this system doesn't always work. Why? The key word here is should. So I'll start with what are the communication requirements (the shalls) are.
I started with searching the FARs (shorthand for the Code of Federal Regulations, specifically chapters for the Federal Aviation Administration, Department of Transportation, => SUBCHAPTER F--AIR TRAFFIC AND GENERAL OPERATING RULES, => 91.1 to 91.1507 GENERAL OPERATING AND FLIGHT RULES.) The FARs say for airports in Class E or G airspace that (d) Communications with control towers. Unless otherwise authorized or required by ATC, no person may operate an aircraft to, from, through, or on an airport having an operational control tower unless two-way radio communications are maintained between that aircraft and the control tower.
But we're talking about airports WITHOUT control towers.
The AOPA guide to Collision Avoidance, Strategies and Tactics, states:
Nearly 45 percent of collisions occur in the traffic pattern and of these, 76 percent occur during approach and landing – when aircraft are on final or actually on or over the runway. Given the small funnel of airspace airplanes occupy during landing, any confusion about who’s landing in what order, and where they are, can have tragic consequences. If there is any consolation about collisions occurring during landing, it’s that there are often survivors.
MACs can also occur while maneuvering in the traffic pattern as a result of improper or misunderstood position reports, which can lead to erroneous assumptions. This is particularly true at nontowered airports. A pilot may conclude, for example, that no aircraft are in the pattern because of lack of activity on the frequency. But aircraft without radios may be operating at these airports, or an inbound or outbound aircraft may be transmitting on the wrong frequency.
Sounds pretty unsafe, doesn't it? So first, let me explain what Class E or G airspace is (I will refer to another AOPA guide, which is extremely helpful in understanding airspace). In the early days of aviation, all airspace was uncontrolled, what we today call Class G airspace. Way back when, there were few airplanes, and none had the instruments necessary to fly in clouds. Even at the busiest of airports, traffic density was very low, and the airplanes flew slowly. With the advent of inexpensive gyroscopic flight instruments, travel through the clouds became possible. See and avoid was useless in the soup, so procedures to ensure aircraft separation were needed. This led to the creation of air traffic control (ATC) and controlled, or Class E, airspace.
Since the FARs doesn't answer the "shall" for our nontowered airports, here is a compilation of different paragraphs from the AIM for brevity:
There are Class E airspace areas that serve as extensions to Class B, Class C, and Class D surface areas designated for an airport. Such airspace provides controlled airspace to contain standard instrument approach procedures without imposing a communications requirement on pilots operating under VFR. IFR operations in any class of controlled airspace requires that a pilot must file an IFR flight plan and receive an appropriate ATC clearance. Standard IFR separation is provided to all aircraft operating under IFR in controlled airspace. Traffic advisories will be provided to all aircraft as the controller's work situation permits. No specific equipment required by the airspace.
What does all that mean? It means that pilots operating at such an airport have no requirement to self announce. In fact, they are not even required to have a radio installed in their airplane! (Class G airspace is even less restrictive than E.) See The FAAs Instrument Flying Handbook for an easy to read chart on the requirements of each airspace. But they should, do the following, according to the AIM:
c. Recommended Traffic Advisory Practices
1. Pilots of inbound traffic should monitor and communicate as appropriate on the designated CTAF (Common Traffic Advisory Frequency) from 10 miles to landing. Pilots of departing aircraft should monitor/communicate on the appropriate frequency from start-up, during taxi, and until 10 miles from the airport unless the CFRs or local procedures require otherwise.
Should does not necessarily mean does.
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UNICOM (No Tower or FSS)
Communicate with UNICOM station on published CTAF frequency (122.7; 122.8; 122.725; 122.975; or 123.0). If unable to contact UNICOM station, use self-announce procedures on CTAF.
Before taxiing and before taxiing on the runway for departure.
10 miles out. Entering downwind, base, and final. Leaving the runway.
So where is the "shall." The shall comes from the dangerousness of operating an airplane. The whole prohibition against operating in a reckless manner. Of course, any pilot concerned with safety would self announce! Yet I have been surprised by traffic at an airport after not hearing any radio calls from them, despite the comment below "Do you really think that I'm not going to tell you I'm there if you don't say ATITAPA?" Here's why, according to AOPA: At nontowered fields, it’s possible that pilots in nonradio aircraft are practicing landings, IFR students and their instructors are practicing instrument approaches, helicopter pilots are perfecting their autorotation skills, or sailplanes are floating overhead. Not all pilots in the area are announcing their positions and intentions on the CTAF, or even looking out the window!
But let's give every one the benefit of the doubt and say they DID self announce. Perhaps their transmission was blocked. Maybe they were busy doing something else and didn't hear someone else in the pattern. Or they have tuned up the wrong frequency (it happens). Maybe they had made their call right before the arrival pilot switched to the CTAF frequency. (Obviously this is an imperfect system or we wouldn't have this problem.) How is this last one possible? If the pilot is operating out of their home airport, or traveling between two airports under VFR, this is facilitated by the pilot making their own frequency changes. Under IFR (in most conditions), pilots are directed to change frequencies, depending on whose airspace they are flying through.
4-1-5. Communications Release of IFR Aircraft Landing at an Airport Without an Operating Control Tower
Aircraft operating on an IFR flight plan, landing at an airport without an operating control tower will be advised to change to the airport advisory frequency when direct communications with ATC are no longer required. Towers and centers do not have nontower airport traffic and runway in use information. The instrument approach may not be aligned with the runway in use; therefore, if the information has not already been obtained, pilots should make an expeditious change to the airport advisory frequency when authorized.So, in the anonymous comment below where it states "I'm too busy to listen and monitor CTAF," even AOPA admits this may be true (not an excuse, but a statement of fact). But that comment neglects to consider that the inbound aircraft may be currently "busy" communicating the overlying ATC frequency (as they are required to do) and may be trying to monitor their destination airport on the second radio (if they have one installed). So when they tune up the appropriate CTAF frequency (before told to switch by ATC), they may have to turn it off in order to hear on their primary frequency.
Especially when, as the anonymous person states, "with the number of airports that use the same CTAF frequency now you can hear traffic calls for airports 80 miles away." As a general rule, when I am 80 miles away from my destination airport, I can still be above 20,000ft, still up in the Class A airspace. So on some CTAFs I can hear numerous transmissions within a wide radius. Especially on a sunny weekend afternoon, radio calls are a jumble, and having pilots step on each other results in an irritating background noise that can prevent me from hearing ATC call me. And so, I will monitor when I can, but my legal responsibility is to the controller whose airspace I am currently occupying. There are times that the controller does not release the IFR traffic until the destination airport is in sight, and due to different limitations (not the least of which may be the transient pilot's unfamiliarity with the airport environment), this can be not until the pilot is almost on top of the airport at the minimum vectoring altitude (which could be near traffic pattern altitude)!
It's unfortunate that this topic causes people to respond defensively. I admitted I was wrong using "All traffic in the area please advise" and expressed my desire to be aware of other traffic in my concern for safety. As I remember from my childhood, as a pedestrian you may have the right of way, but being hit by an errant car still makes you dead. Whatever we can do to prevent mid-airs should be every pilot's goal. Even if making another radio call appears redundant, molley-coddling, etc., or might make you or the other pilot appear stupid, Mid Air Collisions still happen - type a search for Mid Air Collisions on final and you'll get many hits (airplane pictures are from this site). I am in complete agreement that everyone should stay away from unnecessary transmissions, As AOPA says in their Safety Tip:
The CTAF should be used for two reasons only
• Collision avoidance
• Airport advisory
Listening to a busy CTAF for only a few minutes will reveal too many long-winded conversationalists. Don’t use this vital collision-avoidance resource for aircraft or lunch scheduling, formation flying, saying hello to friends on the ground, discussing sports scores, or expressing your displeasure at the pilot who just pulled out on the runway while you were on short final.
So use the radio for collision avoidance, which is our ultimate goal, is it not?
(Note: the unfortunate consequence of discussing these aviation subjects is that I try to stay somewhat superficial to keep the posts brief. If I appear to be incomplete - or worse, as if I don't know what I'm talking about - it is probably because getting any deeper into the weeds creates new tangents that I often try to follow through in subsequent entries. I just cannot include every possibility or scenario so I include links to references for you to do your own research. Thank you to those who respond to clarify my answers, sources, positions, etc. We all have opinions, knowledge and experiences to contribute to the "conversation." I write this blog to learn and share, and I hope the readers do as well.)