What is the equation used when leading a turn from an arc?

What is the equation used when leading a turn from an arc?

• A. 1/2 of 1% of GS x (60/DME of Arc)
• B. 1% of GS x (60/DME of Arc)
• C. GS x arc length
• D. 2% of GS x (60/DME of Arc)

Answer: (A)

Leading a turn from an arc means you start turning before you reach the end of the arc so you roll out on the next course exactly where you want. The rule of thumb used here says to take half of one percent of your current ground speed and multiply it by sixty divided by the arc length in DME. This combination converts how far you’re flying along the arc (the DME) into a lead distance that scales with both speed and arc length. The 60/DME factor turns arc distance into a time-like cue, so faster airspeeds or longer arcs increase the lead proportionally, giving a smooth, predictable rollout onto the next leg. Using this approach keeps the lead distance reasonable across typical speeds and arc lengths, whereas using a simple GS times arc length or a larger percentage would not reflect how the arc geometry and speed interact.

Leading a turn from an arc means you start turning before you reach the end of the arc so you roll out on the next course exactly where you want. The rule of thumb used here says to take half of one percent of your current ground speed and multiply it by sixty divided by the arc length in DME. This combination converts how far you’re flying along the arc (the DME) into a lead distance that scales with both speed and arc length. The 60/DME factor turns arc distance into a time-like cue, so faster airspeeds or longer arcs increase the lead proportionally, giving a smooth, predictable rollout onto the next leg. Using this approach keeps the lead distance reasonable across typical speeds and arc lengths, whereas using a simple GS times arc length or a larger percentage would not reflect how the arc geometry and speed interact.