KC-135 Gouge



APPENDIX: Circling

1. A circling approach is defined as a visual maneuver (not VFR) performed after accomplishing an instrument approach to align the aircraft with the landing runway.

Most of us have been taught that a circle is simply a maneuver at the end of a straight-in approach that cannot be completed as a straight-in. Although this statement is in some cases correct, it can also be quite misleading.

Why would we ever want to execute circling approach? Because strong winds may favor a runway that does not have a straight in IAP

What is the difference between a procedure named VOR-A and VOR-B? There is no difference. The first procedure created will have the suffix A even though there might not be intentions to formulate additional procedures.

2. Circling Approaches are inherently dangerous maneuvers. Some airlines won’t allow their crews to circle because of the risks involved. American requires 1000/3. What makes circling approaches so difficult?

a. We rarely practice them

b .Low speeds

c .Low altitudes

d .Poor visibility

e .High cockpit workload

f .Usually unplanned

3. From a procedure planner's viewpoint:

a. A straight-in approach provides lateral guidance to a runway

b. A circling approach procedure provides lateral guidance to an airfield - and that's an important distinction.

c. At the termination of a straight-in approach, either at the DH or VDP, you complete the landing with little or no maneuvering. Once visual on a circling approach, you must visually maneuver your aircraft to land.

4. Types of Circling:

a. You can fly a straight-in approach to one runway and then use the circling MDA published on the IAP to circle to any runway on the field as long as you comply with published restrictions.

b. You can also fly a published circling approach (such as a VOR-A, TACAN-A) and maneuver to the landing runway. In this latter case the instrument procedure does not meet the criteria for a straight-in landing. This criteria is:

1. A maximum 400 ft/NM descent gradient from the FAF to runway threshold

2. A final approach course within 30° of the runway heading.

3. Final approach course doesn’t cross extended runway centerline prior to the runway threshold.

c. High terrain close to the runway can cause high FAF altitudes even though the electronic guidance is lined up. In this case the 400ft/nm descent gradient will be satisfied from FAF altitude to the circling MDA.

5. Aircraft Performance and Category

a. Aircraft performance has a direct effect on the airspace required to accomplish a circling maneuver. Each aircraft is assigned a category based upon its maneuvering speed. You can not decrease your aircraft's category, but if a higher speed is required to maneuver you should go to the next higher category

b. Who decides your category? MAJCOMs assign aircraft categories by way of aircraft technical orders (Dash 1).

c. Where do you find your aircraft approach category? FAR Part 97.3 defines aircraft approach category as a means of grouping aircraft based on a speed of 1.3 VSO (Stalling speed in the landing configuration) at maximum certified landing weight. Also try referencing FLIP GP Section 2-2 (Terms). The categories are as follows:

Category A: Speed less than 91 knots.

Category B: Speed 91 knots or more but less than 121 knots.

Category C: Speed 121 knots or more but less than 141 knots.

Category D: Speed 141 knots or more but less than 166 knots.

Category E: Speed 166 knots or greater.

d. Are these speeds indicated, true or calibrated? Doesn’t really say anywhere, but logic would dictate that they are KIAS because there is really no other way to compare so many different aircraft.

Something to then consider is where you are flying your circling approach. J.F. Kennedy International Airport in La Paz, Bolivia - Circling Minimums for a Category D approach: 14,180’!! What is your TAS at 14,000’!!!

6. Ceiling and visibility required and the circling MDA

a. The weather minimums (ceiling and visibility required) and the MDA to be used for a circling approach are those for the runway to which the instrument approach is flown and not those for the landing runway.

b. How they come up with visibility minimums? Minimum circling and vis for category: A/B = 1nm, C = 1.5 nm, D/E 2nm. Enough so the aircraft can see the runway from their MDA at the outside of their circling maneuvering area

c. What clues do minimums give us about obstacles in our circling area? If circling and straight in MDA’s increase with approach category then the limiting factor is the turning missed approach obstacle environment. If the MDA’s are the same then the limiting factor may be an obstacle on the straight ahead portion of the missed approach. When mins of 1 mile or greater for a straight in, there could be something higher than the glide slope inside the DH point. In theory a tower could be at the runway threshold that require higher than normal descent path.

At airports with a relatively high HAA specified for the circling minimums, there is an obstacle slightly more than 300 ft below the MDA. You don’t know where this obstacle is. It could be on your proposed decent path. If you encounter an approach which would require you to descend below MDA before rolling out on final you might want to reconsider unless you know where all the obstacles are. Early missed approach point MAP combined with an unusually high HAA, indicates that we may get into a performance bind when if we initiate the missed approach after the MAP. That is why it is not a good idea to attempt landings after the VDP.

7. Weather Requirements

a. Circling approaches based on "visibility only" criteria are not authorized. Both the visibility and the ceiling must be at or above those required for the approach before you can either fly or file to a base where a circling approach must be utilized for landing. Visibility only criteria are only used with straight-in approaches to landing.

b. Circling weather minimums are based on the prevailing visibility which is the greatest over 180° of the horizon, not necessarily a continuous 180°. This means that the visibility given you by the tower might not be present in all quadrants; it might be lower causing you to lose sight of the runway during your circling maneuver.

c. Must you go missed approach if you lose sight of the runway? No. You only need to keep the airport environment in sight. This is different from straight-in procedures.

9. Obstruction and Obstacle Clearance areas

a. The circling approach MDA/HAA provides a minimum of 300ft obstruction clearance for all categories. There is a minimum HAA for each category because we don’t want a 747 circling at 300 ft AGL at an airport without obstacles

b. The radii of the arcs that define the protected airspace is determined by the turning radius of the aircraft in each category which in turn is based on the upper limit airspeed of each category.

c. If it is necessary for an aircraft to maneuver at speeds in excess of the upper limit of the speed range for the aircraft's category, the aircraft will probably exceed its protected circling area and should use the minimum for the next higher approach category. You can always use the next higher category's minimums but never the next lower category's minimums.

d. There is no secondary obstruction clearance zone for circling approaches as there is for straight-in approaches. Once an aircraft exceeds the protected circling radius from the runway there is no guarantee of obstacle protection.

e. An obstacle may be present at or above the MDA. STAY WITHIN YOUR CIRCLING AIRSPACE. You must know where you are in relation to the runway by keeping the airport environment in sight. Always keep position oriented. DME is the best aide if it is available.

f. Due to lower required visibility minimums than the radius provided for a specific category aircraft, pilots who fly close to the edge of the circling area can easily find themselves losing sight of the runway.

Even though you can go out 4.5 NM (category E) it might be better to stay within the visibility present during the approach. Keep the airport in sight. Recommend you always practice circling staying within 2 NM. Here’s why:

|Approach Category |A |B |C |D |E |

|Minimum MDA |350 |450 |450 |550 |550 |

|Required Visibility (in miles) |1 |1 |1.5 |2 |2 |

|Circling Area Radii (in miles) |1.3 |1.5 |1.7 |2.3 |4.5 |

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11. Controller Instructions

a. The Air Traffic Control Manual (FAAH 7110.65) tells the controller how to issue circling instructions and what information to include. When the direction of the circling maneuver in relation to the airfield/runway is required, the controller will state the direction (using one of the eight cardinal headings) and specify a left or right base/downwind leg as appropriate.

1. (The controller can either state: "Circle to runway XX" or "Circle SW of the airfield for a left base to runway XX" if there are no restrictions.

2. Once cleared for a circling approach the controller cannot issue instructions that would cause you to exceed your circling protected airspace.

(Examples: "I'll call your base," "Extend your downwind to follow aircraft on final." Controllers often assume an aircraft flying a circling maneuver is "VFR" and is at the normal VFR traffic pattern altitude.

b. Make sure they realize that you are at circling minimums and don't have the obstacle protection provided in the VFR pattern. Don't let a controller lead you astray. It’s up to you to remain within the protected airspace.

12. Restrictions

a. If the approach planners cannot satisfy all the conditions necessary for building a circling approach, a restriction will be included on the approach plate. There are many types of restrictions, and no standardized way of depicting them. They may be very clear or very ambiguous.

1. Direction from runways

2. Direction from runways including the reason for the restrictions

3. Direction from field

4. Restricted by category due to circling area and obstructions present

5. Restricted from circling to a certain runway

6. Complicated restrictions (explain area)

7. Total restriction from circling

b. Radar approach restrictions to circling will be found in the front of the IAP with the circling minimums.

13. Techniques for Establishing Offset

a. You must offset your aircraft in order to safely execute a turn downwind to final. The normal "visual" method will not work.

When can we start our circling maneuver? 11-217: After descending to Circling MDA and when airport environment is in sight, determine if the ceiling and vis are sufficient for performing the circling maneuver. The airport environment is considered: runway, lights, markings, taxiways, hangars etc. No specific place but says to maneuver aircraft to remain within the circling area for your aircraft category. A technique is to wait until you’re within 1nm of the approach end before departing the electronic final approach guidance to ensure adequate visual reference and inside the circling maneuvering area.

One 90° turn to downwind. Fly outbound from the runway the same distance it takes you to make a 90° turn to insure proper offset. Unless the TACAN is right at the field, the only way to determine distance (X) is with timing.

a. Advantages: You can overfly the runway and see the airfield layout.

b. Disadvantages: A tailwind might blow you further than expected. Subtract wind from TAS and use 10% of that for timing in seconds. Circling might not be authorized on one side of the runway.

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Two 90° turns method. First turn can be made when runway is sighted or when over threshold. Correct for drift.

a. Advantages: Just like normal visual pattern. This method guarantees proper displacement as long as drift is corrected for on downwind.

b. Disadvantages: You might lose sight of the runway.

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45° method. Turn 45° off of runway heading, hold heading until abeam threshold of runway, then turn to parallel runway. This gives an offset equal to the length of the runway. If you need less of an offset turn to parallel the runway abeam the proper offset point. Correct for drift on both 45° off of heading and while on downwind. When would you start your base turn? Do you roll out on base to clear final approach?

a. Advantages: The runway is kept in sight. Good procedure for landing on opposite runway.

b. Disadvantages: A short runway might not provide enough offset. Hard to identify when abeam the runway perch point. Also you must cross end of runway to start maneuver.

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30° off heading technique. Turn 30° off of runway heading for four (4) times 10% of your TAS/ groundspeed in seconds.

a. Advantages: You don't need to cross the end of the runway. You keep the airfield environment in sight.

b. Disadvantages: Higher visibilities may be required to set up offset if runway is not seen early enough.

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Turning radius for 90° turn is MACH - 2

MACH = KIAS/60 or 180/60 = 3 NM/min

90° turn radius is: 3 - 2 = 1

How long does it take to travel 1 NM at 3 NM/min?

(20 seconds)

Time for 20 seconds after passing runway and then turn to parallel runway.

Easier way is to take 10% of KTAS.

10% X 180K TAS = 18 seconds.

This is not only easier but faster and no real mental gymnastics are needed.

Establishing a base leg. If your alignment does not require excessive maneuvering (less than 90°) you may just maneuver into a base leg if visibility is adequate. DME will almost be a necessity. Remember, if weather permits you to climb to a standard VFR pattern altitude, your approach will be easier to fly because the visual references will be familiar. Be careful with visual illusions or sloping terrain.

14. Problems Encountered During Circling.

a. The visual problems associated with attaining sufficient lateral displacement from the runway cannot be overemphasized. There is a tendency to get too close to the runway, closer than a normal visual pattern. Your normal perspective/picture of the runway is seen from 1500' AGL (typical) not 550' AGL (HAA) while on downwind. This makes the pilot fly closer to the runway to make the picture look the same and see the same perspective. This condition will cause the pilot to maneuver too close to the runway to make a 180° turn without overshooting the runway even though the picture "looks about right." The best method of solving this problem is, if weather permits, to fly the entire circling maneuver at your normal VFR traffic pattern altitude. This will give you the same visual cues and will allow you to "normalize" the approach. If weather will not allow a VFR pattern, use one of the offset techniques and believe it.

b. Another possibly dangerous situation is descending too soon (leaving the circling MDA prior to intercepting a normal glide path) on base leg. The circling MDA for category D aircraft can be as low as 550' HAA. If you were to descend as you start your turn to base at this altitude you might not only lose sight of the runway environment, but you might hit the ground. AFM 11-217 says to descend from the circling MDA when in a position to place the aircraft on a normal glide path to the landing runway. Does this sound familiar? It is very similar to the philosophy of the VDP. The VDP, normally only used with straight-in approaches, can be used to keep from descending too soon on a circling approach. Using your circling MDA, determine how far from the runway you would intercept a normal 3° glide slope. When you have VASIs , Aim 2-1-2: Safe obstruction clearance within plus or minus 10 degrees of the extended runway centerline and to 4nm from the runway threshold. Nothing is said about PAPI’s . There is an advisory circular advising airport operators to provide the same criteria as the VASIs. The 400ft/nm gradient is calculated only to the circling MDA, so you need to calculate how far out you need to start your descent from the MDA to landing. If you depart the circling MDA on downwind or base you are on your own. The FAA makes no guarantees. You only have some protection on the final approach area. If you have VASI or PAPI you are in good shape if within 10deg of centerline and 4 nm. This is also the case if the runway has straight-in minimums < ¾ mile on a different IAP. If you don’t have any of these conditions then once you are 300ft below MDA you could hit anything up to the runway threshold.

c. If there is a TACAN present on the field you can now convert this to DME. Now you know that you should not descend from your MDA until you are at the VDP distance from the runway. If the visibility is good enough, you can extend your downwind leg so that you can fly a level base leg and roll out on final prior to reaching the computed VDP.

d. What does a restricted sector imply? If the IAP restricts you from maneuvering on a given sector, in theory, you could have an obstacle you could hit on final just to the restricted side of the runway centerline. (N/A for VASI/PAPI). You might be better off undershooting your turn to final.

15. Missed Approach

a. If there is any doubt whether the aircraft can be safely maneuvered to touchdown, execute the missed approach.

b. When you go missed approach, follow the missed approach procedure specified for the instrument approach just flown unless otherwise directed. An initial climbing turn toward the landing runway will assure that the aircraft remains within the protected circling area. Continue to turn until established on the published missed approach course/heading.

c. Obstacle clearance area provided for the missed approach is predicated upon the missed approach being started at the MAP.

When the missed approach is initiated prior to the MAP, proceed to the MAP along the final approach course and then via the route and altitudes in the IAP. If we lose sight of the runway environment during our circling maneuver we need to make an initial climbing turn toward the landing runway and continue the turn until established in the Missed approach course. This extra maneuvering close to the runway ensures advantage in obstacle clearance due to the climb close to the protected airspace.

We follow the missed approach procedure for the particular instrument approach we used for the circle. At unfamiliar fields, it should be a max performance maneuver. If we climb at the minimum rate required for the 40:1 slope then no pad is provided when obstacles get progressively higher beneath this slope.

16. Runway/Airfield Environment

What is the difference between runway and airfield environment?

Runway environment (AFM 11-217). This is the runway threshold or approved lighting aids or other markings identifiable with the runway.

Runway environment (FAR § 91.175):

1. The approach light system.

2. The threshold.

3. The threshold markings.

4. The threshold lights.

5. The runway end identifier lights.

6. The visual approach slope indicator.

7. The touchdown zone or touchdown zone markings.

8. The touchdown zone lights.

9. The runway or runway markings.

10. The runway lights.

Airport environment (AFM 11-217). This is the runway(s), its lights and markings, taxiways, hangars, and other buildings associated with the airport.

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APPENDIX

Circling

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