See AC 90-66A - RECOMMENDED ‘STANDARD TRAFFIC PATTERNS AND PRACTICES FOR AERONAUTICAL OPERATIONS AT AIRPORTS WITHOUT OPERATING CONTROL TOWERS for information about uncontrolled airport traffic patterns.
It includes the following which says that while the FAA recommends using the full pattern, it is not required: 7.
GENERAL OPERATING PRACTICES.
a. Use of standard traffic patterns for all ‘aircraft and CTAF procedures by radio-equipped aircraft are recommended at all airports without operating control towers.
However, it is recognized that other traffic patterns may already be in common use at some airports or that special circumstances or conditions exist that may prevent use of the standard traffic pattern
And then: e.
The FAA encourages pilots to use the standard traffic pattern.
However, for those pilots who choose to execute a straight-in approach, maneuvering for and execution of the approach should be completed so as not to disrupt the flow of arriving and departing traffic.
Therefore, pilots operating in the traffic pattern should be alert at all times to aircraft executing straight-in approaches.
f. Pilots who wish to conduct instrument approaches should be particularly alert for other aircraft in the pattern SO as to avoid interrupting the flow of traffic.
Position reports on the CTAF should include distance and direction from the airport, as well as the pilot’s intentions upon completion of the approach
aviation.stackexchange.com/users/69/Lnafziger
I'd like to answer your question with a short example.
A few days ago I flew to Venice (untowered) and decided to make a teardrop entry to set up for the 45.
My calls were 10 and 5 miles out, both ending with "any traffic please advise.
" Guess what I saw overtaking me on my 4 o'clock position only a few hundred feet away at same altitude (500 feet above pattern)?
It is legal to make a straight in, but before you think about the time or fuel you waste please think about your own and even the guys who's not on CTAF and obviously heads down safety.
If you fly the 45 and the continue the pattern (it's not always left, check your sectional and the A/FD)
everybody knows what the other one is doing and if necessary can act accordingly.
aviation.stackexchange.com/users/343/Falk
It is legal.
The left downwind pattern entry at a 45 degree angle is recommended in the AIM to standardize operations and is therefore not regulatory in nature.
However, the reason it's not a particularly good idea is that not all aircraft are required to have radios at a non-towered airport.
A traffic pattern is quite small compared to the en route phase or an instrument approach, there's not much time or fuel to be wasted.
aviation.stackexchange.com/users/338/belowMins
Nobody on the radio does NOT mean no traffic.
You have IFR Arrivals not yet released by approach to tower frequency, and you have 100% legal no radio aircraft.
Fly the pattern so that they know where to look for you!
aviation.stackexchange.com/users/291/Skip Miller
There are a few airports out there with this line in their AF/D page: STANDARD TFC PATTERN REQUIRED OF ALL ACFT.
Such as KMBT, as seen here.
Not sure how legally binding this is, but it is written.
aviation.stackexchange.com/users/277/StallSpin
It is recommended in the AIM and elsewhere that you use the traffic pattern.
However, the FAR requires only that you make any turns in the proper direction, not that you fly the pattern or enter the pattern on downwind.
Straight in approaches are not prohibited.
(91.126) "Unless otherwise authorized or required, each person operating an aircraft on or in the vicinity of an airport in a Class G airspace area must comply with the requirements of this section....
When approaching to land at an airport without an operating control tower in Class G airspace...
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;" "Otherwise authorized or required" applies to circling approaches, in which turns may be made in any direction (opening up a whole new set of risks).
Safety and common sense may dictate that you fly the pattern as a matter of practice.
It is also safer to announce your position, and to announce "left (or right) downwind" and "left (or right) base", in case you or the plane you don't see happens to be going the wrong direction.
aviation.stackexchange.com/users/110/xpda
If there seems to be very little traffic at an untowered airport, and no one's replied to any of your radio calls, is it acceptable to just fly a straight-in approach to the runway, or should you still fly the full traffic pattern to final? It just seems like it would be a waste of time and fuel when it's not really necessary. Is there anything wrong with doing so?
Is a full traffic pattern required when there is no traffic at an untowered airport?
aviation.stackexchange.com
<approach><traffic-pattern><non-towered-airport>
aviation.stackexchange.com/questions/622
aviation.stackexchange.com/users/72/Qantas 94 Heavy
Use of standard traffic patterns for all ‘aircraft  and CTAF procedures by radio-equipped aircraft  are  recommended at all airports without operating  control towers.  While it is legal not to, all advice points towards doing a full traffic pattern.
Users suggest that it is necessary Users suggest it is legal not to