Visual Indicators at Uncontrolled Airports
(AIM 4-53)
DON'T MISREAD WINDSOCK, TETRAHEDRON, OR SEGMENTED CIRCLE!!!!
a. At those airports without an operating control tower, a segmented circle visual indicator system, if installed, is designed to provide traffic pattern information. The segmented circle system consists of the following components:
1. The segmented circle--Located in a position affording maximum visibility to pilots in the air and on the ground and providing a centralized location for other elements of the system.
2. The wind direction indicator--A wind cone, windsock, or wind tee installed near the operational runway to indicate wind direction. The large end of the wind cone/wind sock points into the wind as does the large end (cross bar) of the wind tee. In lieu of a tetrahedron and where a windsock or wind cone is collocated with a wind tee, the wind tee may be manually aligned with the runway in use to indicate landing direction. These signaling devices may be located in the center of the segmented circle and may be lighted for night use. Pilots are cautioned against using a tetrahedron to indicate wind direction.
Small windsocks have 15-knot limit for stiffening. Droop is only way to make lower estimates. Use 45-degree droop as 7-8 knots. For takeoff estimate crosswind heading correction as one degree for each knot of crosswind.
Headwind factor of sock 30 degrees off runway heading means that wind velocity is only 75% of a headwind. Up to 60 degrees off runway heading means the headwind velocity is only half as strong. Beyond 60 degrees wind is zero headwind.
Crosswind factor of sock 30 degrees off runway heading means that wind velocity is 50% directly into wind. Estimate a wind between 30 and 60 degrees as 75% of direct wind velocity. Give wind full value if beyond 60 degrees.
Tailwind off 30 degrees is estimated as full strength. Up to 60 degrees off tail is estimated at 75% base velocity. Over 60 degrees wind is estimated as 50% of base velocity.
Select a wind direction and draw in the appropriate diagrams for the words.
Runway
segmented
circle
wind tee
wind sock
3. The landing direction indicator--A tetrahedron is installed when conditions at the airport warrant its use. It may be used to indicate the direction of landings and takeoffs. A Tetrahedron may be located at the center of a segmented circle and may be lighted for night operations. The small end of the tetrahedron points in the direction of landing. Pilots are cautioned against using the tetrahedron for any purpose other than as an indicator of landing direction. Further, pilots should use extreme caution when making runway selection by use of a tetrahedron in very light or calm wind conditions as the tetrahedron may not be aligned with the designated calm-wind runway. At airports with control towers, the tetrahedron is lockable and should only be referenced when the control tower is not in operation. Tower instructions supersede tetrahedron indications. Make illustration showing positions as though wind is from the west.
tetrahedron
4. Landing strip indicators--Installed in pairs...and used to show the alignment of landing strips (runways)
Wind sock
5. Traffic pattern indicators--Arranged in pairs in conjunction with landing strip indicators and used to indicate the direction of turns when there is a variation from the normal left traffic pattern. (If there is not segmented circle installed at the airport, traffic pattern indicators may be installed on or near the end of the runway.)
Draw a segmented circle with runways going east and west. Draw the base legs to the runways so that the 270 degree heading base leg is for right traffic and 090 runway base leg is also right traffic.
b. Preparatory to landing at an airport without a control tower, or when the control tower is not in operation, the pilot should concern himself with the indicator for the approach end of the runway to be used. When approaching for landing, all turns must be made to the left unless a traffic pattern indicator indicates that turns should be made to the right. If the pilot will mentally enlarge the indicator for the runway to be used, the base and final approach legs of the traffic pattern to be flown immediately become apparent. Similar treatment of the indicator at the departure end of the runway will clearly indicate the direction of turn after takeoff.
c. 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 (FAR 91.113(f)).
Uncontrolled Airport Traffic Patterns
At most airports and military air bases, traffic pattern altitudes for propeller-driven aircraft generally extend from 600 feet to as high as 1,500 feet above the ground.... Therefore, pilots of enroute aircraft should be constantly on the alert for other aircraft in the traffic patterns and avoid these areas whenever possible. Traffic pattern altitudes should be maintained unless otherwise required by the applicable distance from cloud criteria (FAR 91.155)
A disproportionate number of near-midair collisions and actual collisions occur at uncontrolled airports. Any pilot arriving at such an airport should pre-plan his arrival and have the cockpit so organized that maximum attention can be given outside the cockpit. Seeing is harder in an unfamiliar situation that avoidance of what you see. My using standard procedures you can better know where to look and what to look for.
As a former schoolteacher I have memories of playing a visual game with my classes on rainy days instead of going outside for P.E. I would have one group of children put their heads down. Another child would take a common object such as a key and place it in an uncommon place such as on a shoe, head, door knob, or projecting from a crack. On signal the selected group would raise their head and walk around the room trying to see the object. As the different children would find the key, they would return to their seats without letting those still looking know that they found the key. The quietest of the remaining groups would get to put their heads down next. The children enjoyed the increasing tension and the emotional control required not revealing they had found the key. Neat game to tell any teachers you know.
The reason I tell the story of the game is that, always the same children seemed to have the ability and skill to find the keys first. There is a special skill in looking, seeing, and then recognizing what you have seen. In my opinion, you have the required innate ability/skill or not. Some of my students have consistently exceeded my ability to spot aircraft. Physical conditions can be a negative/positive factor. The size, glare, and clarity of the windshield, the existence or non-existence of haze will make a difference. Knowing where to look is an intellectual factor that any pilot can develop.
The most effective scan covers no more than 10 degrees of the window and proceeds in successive 10-degree jumps. You cannot see when your eyes are moving. The eyes must stop and focus for a moment in order to see. A broad scan must be done by moving the head and keeping the eyes stationary. Additionally the focus distance (accommodations) must be varied from close to far. This is most important when haze give an obscure view of distant objects. Looking too long for distant objects in such conditions will cause the eyes to re-focus at about 20 feet. Learn to react to things in your peripheral vision even if it is a bug splatt. Any aircraft that balloons in your vision without moving is going to hit you, just like the runway.
Traffic Indicators
--At night or any other time, an orange light is on top of the windsock.
--The white traffic pattern indicators at right angles to the landing strip indicators show that a right turn is required.
--Traffic pattern indicators may be installed on or near the end of the runway.
While the 45-degree entry is recommended, the FAA has no suggestion as to how to arrive at the initiating point when no advisory can be obtained. You should first overfly at twice pattern altitude to confirm wind direction and the pattern direction of the preferred runway. There are two ways I have seen the initial 45 entry reached. Every key point of each procedure should be identified for other traffic.
1. At twice pattern altitude, cross over the runway at a 90 degree angle toward the downwind leg, cross that leg and fly on this heading at least another mile before turning 90 degrees parallel to the runway toward the upwind end. At the 90-degree turn descent to the pattern altitude should be initiated. Eyeball for a 45-degree angle to the approach end and make your turn of 135 degrees. For left traffic this will combine two right turns, the first of 90 degrees and the second of 135 degrees. Draw this out around a diagram of an airport to see how it put you on a 45 entry.
What I Dislike in This Option
a) I have had an instructor use it without allowing for a strong cross wind. His turn to parallel the downwind put us right into the downwind traffic pattern.
b) The necessity for right turns restricts the see-and-be-seen requirement.
2. From the approach end of the field depart on a heading that will take you across the pattern side of the field on a 45-degree angle toward the point of entry. You will be on this heading if the runway # (number) is on the right front 45-degree mark of your heading indicator. Proceed on this heading until clear of the pattern and descend 500'. Initiate a course reversal (a required private pilot procedure) first 90 degrees to the right which would be away from the traffic and airport and then a 270 to the left back to the entry position. On a correct 45 degree heading the runway # number will be on your left rear 45 degree heading marker. This inbound checking system works for all 45-degree entries left and right..
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