It Doesn't Mean Rule Free
A lot of general aviation flying is done into and out of airports that do not have air traffic control towers. In fact, of the more than 18,000 airports in the United States, only about 350 of them have towers that are manned by FAA air traffic controllers. Therefore, it is reasonable to expect that during your flying career you will perform many operations at airports without traffic control towers. It is important to learn about the regulations and recommended procedures that apply to flights when there is no controller giving you instructions.
The regulations that apply to approaching a nontowered airport are relatively straightforward and simple, but they don't seem to provide all the procedures that you need to conduct this operation. Parts 91.126 and 91.127 of the federal aviation regulations (FARs) contain provisions that specifically apply to operating on or in the vicinity of an airport without an operating control tower. In particular, these regulations state that when approaching to land at such an airport, "Each pilot of an airplane must make all turns of that airplane to the left unless the airport displays approved light signals or visual markings indicating that turns should be made to the right, in which case the pilot must make all turns to the right. Each pilot of a helicopter must avoid the flow of fixed-wing aircraft."
In addition, FAR 91.113 sets out right-of-way procedures and see-and-avoid principles that apply to operating at nontowered airports ("Who's Got the Right of Way," August 1999 and "See and Avoid," April 1999 AOPA Flight Training). And, FAR 91.111(a) directs against operating an aircraft so close to another aircraft as to create a collision hazard.
Now, let's look at procedures that are not prescribed by the regulations but are recommended by the FAA for how aircraft should approach and land at nontowered fields. The FAA recommends a standard traffic pattern for airplane operations at nontowered airports, which the FAA describes in the Aeronautical Information Manual and in Advisory Circular 90-66A. The standard traffic pattern uses a 1,000-foot agl pattern altitude that is maintained until abeam the approach end of the landing runway on the downwind leg. The pattern begins with a 45-degree entry to a downwind leg abeam the midpoint of the runway, followed by a base leg at a right angle to the landing runway, and then a final approach leg to the runway that begins at least one-quarter of a mile out from the approach end of the runway.
Note that this is the FAA's recommended pattern and does not have the force and effect of law. So, as a matter of law, a pilot can approach a runway straight in or make any pattern that the pilot deems safe or that may be customarily followed at a particular airport, so long as turns are made in the proper direction. It is especially important to remember this anytime you're in the pattern at a nontowered airport, as you may be on the downwind or base leg while another aircraft is approaching the runway straight in. As a matter of practice, most pilots adhere to a fairly standard pattern at nontowered airports, and most pilots do a good job of announcing their locations in the pattern over the unicom or common traffic advisory frequency.
So, the regulations provide a basic framework to help to keep pilots vigilant and organized. But, they don't provide all of the guidance necessary to safely complete an approach and landing to a nontowered airport. Therefore, we may be guided by the standard traffic pattern that the FAA recommends as well as other resources that provide specific pattern information for particular airports. Much of this information can be found in official sources such as the Airport/Facility Directory, as well as unofficial ones, including AOPA's Airport Directory. You should gather this information be-fore you depart. But in a pinch, you can inquire over the airport unicom or just listen to the calls of other pilots. After that it's up to you, the pilot in command, to exercise good judgment.