9.20. Introduction Common terminology and concepts applicable to formation flight are used throughout the Air Force. The following are fundamental concepts:

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9.20.1. Stabilized. In control and able to complete the maneuver safely within the pilot’s capabilities. Number 2 is often directed to stabilize before continuing a maneuver. For example, number 2 must stabilize in route before continuing to fingertip during a rejoin. “Stabilize” does not mean stop; it means “under control”.

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9.20.2. Heading Crossing Angle (HCA) (Figure 9.3.). The angular difference between the longitudinal axes of two aircraft. (HCA is also synonymous with the term “angle off”.)

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9.20.3. Aspect Angle (AA) (Figure 9.3. and Figure 9.4.). Aspect is expressed in degrees off the tail of the reference aircraft, commonly expressed in multiples of 10. For example, at 6 o’clock to the reference aircraft, the aspect is zero. At 40 degrees left, the aspect is “4L”. AA is not a clock position and is independent of aircraft heading. Two important AAs used extensively in T-6 training are 30 and 45 degrees (Figure 9.5). (Note position of the vertical stabilizer on the outside wing.)

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9.20.4. Closure. Overtake created by airspeed advantage and (or) angles; the rate at which range decreases. Closure can be positive (decreasing range) or negative (increasing range), and is usually measured by the velocity rate (knots) at which the range increases/decreases.

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9.20.5. Lift Vector (Figure 9.6.). The vector that is always positioned straight through the top of the canopy. The magnitude is based on G loading. In the T-6, use the CFS cord as a reference to indicate where the lift vector is pointed.

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9.20.6. Velocity Vector (Figure 9.6.). Where the aircraft is going. The magnitude of the velocity vector is controlled by changing airspeed.

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9.20.7. Line of Sight (LOS). A straight line from the pilot’s eye to another aircraft. Commonly expressed as “forward LOS” (other aircraft moving forward on canopy toward the nose) and “aft LOS” (other aircraft moving aft on the canopy toward the tail).

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9.20.8. LOS Rate. The speed at which forward or aft LOS is occurring, expressed with adjectives rather than a unit of measurement. (For example, “rapid, aft LOS”.)

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9.20.9. Plane of Motion (POM). The plane containing the aircraft flight path. In a level turn, the aircraft’s POM is parallel to the ground, regardless of bank angle. In a loop, the POM is perpendicular to the ground (Figure 9.7.).

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9.20.10. Lead Pursuit (Figure 9.8). Number 2 aims the aircraft nose in front of number 1’s flight path. With enough lead pursuit, AA and closure will increase, and HCA will decrease. Various lead pursuit pictures may result in aft LOS, no LOS, or minimal forward LOS depending on the magnitude of lead pursuit and other parameters such as relative airspeed and G.

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9.20.11. Pure Pursuit (Figure 9.9). Number 2 aims the aircraft nose directly at number 1. In pure pursuit there is initially no LOS; the other aircraft remains fixed at 12 o’clock in the canopy. A pure pursuit picture initially creates closure that diminishes over time. AA equals HCA, which also both diminish over time. If both aircraft are co-airspeed, sustained pure pursuit will eventually put number 2 on a zero aspect in a tail chase of number 1

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9.20.12. Lag Pursuit (Figure 9.10). Number 2 aims the aircraft flight path behind number 1’s flight path. Although there may still be some closure initially, closure soon decreases, AA decreases, and HCA increases.

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9.20.13. Vertical Lead/Lag/Pure Pursuit (Figure 9.11.). Number 2 has basically three options in pursuit of number 1 during vertical maneuvers. Depending on the current energy state number 2 can pull vertical at the same spot number 1 did to get pure pursuit. If number 2 needs to pull lead then number 2 will go vertical prior to the point in space number 1 started the vertical maneuver. To pull lag number 2 will wait until beyond the point in space number 1 started the vertical maneuver.

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9.20.14. Aircraft 3/9 Line (Figure 9.12). This is an imaginary line extending from the aircraft’s lateral axis (parallel to the wings and perpendicular to the fuselage). The numbers “3” and “9” have reference to clock position. Number 2 should normally remain aft of number 1’s 3/9 line during maneuvering. This line equates to a 90-degree AA (9 aspect).

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9.20.15. Turn Circle. As an aircraft maneuvers in a turn, the flight path describes an arc, referred to as a turn circle.

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9.20.16. Turn Rate. This is the rate of heading change (nose track), normally measured in degrees per second. At about 10,000 feet MSL, at 30-degree bank, 180 KIAS (i.e., a normal turning rejoin), the T-6 turn rate is approximately 3 degrees per second.

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9.20.17. Turning Room. This is the volume of airspace (vertical and horizontal) that is available to execute maneuvers that change aspect, angle off, and closure. In the T-6, turning room is mostly used aft of number 1’s 3/9 line.

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9.20.18. Safe Airspace. Generally, this is an area where any immediate threat of collision is unlikely if an out-of-plane maneuver is initiated. Pulling toward number 1’s high six o’clock is a common example of safe airspace for number 2.

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9.20.19. Lag Reposition (High Yo-Yo) (Figure 9.13). A high yo-yo is a reposition of number 2’s aircraft that uses various combinations of pursuit and a move out-of-plane above number 1’s POM to control closure and aspect to prevent a potential 3/9 line overshoot. It creates turning room by using the vertical POM (out-of-plane). Creating a large HCA will result in a rapid increase in range. A high yo-yo is often used when number 1 initiates a turning rejoin into the number 2 aircraft. Number 2 uses the vertical turning room to preserve energy while staying inside (typically, depending on range and aspect) of number 1's turn circle.

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9.20.20. Quarter Plane (Figure 9.14). Much like a high yo-yo, a quarter plane is an aggressive, last ditch, out-of-plane lag maneuver used to control closure and aspect in order to preserve the 3/9 line. In a true quarter plane, number 2 establishes a POM that is 90 degrees to number 1’s POM. This situation may be caused by a late decision (or no decision) to execute a high yo-yo or a failure to control closure and aspect. Indicators that a quarter plane is needed are similar to those of a high yo-yo. However, aspect, HCA, range, and closure cues are more significant and require a much more aggressive maneuver than a lag reposition. A large HCA will result in a rapid increase in range. Caution should be used to maintain visual contact with number 1 throughout the reposition maneuver.

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9.20.21. Lead Reposition (Low Yo-Yo) (Figure 9.15). A low yo-yo is a reposition of number 2’s aircraft, using various combinations of pursuit and a move out-of-plane below number 1’s POM to increase closure and AA.

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