FAA Instrument Flight Instructor (FII)IFR Procedures and ApproachesMedium
A pilot is flying a published DME arc as part of an instrument approach. To smoothly roll out on the inbound radial after completing the arc, the pilot should begin the turn how many degrees before reaching the radial that defines the inbound course?
- A10 degrees (lead radial)
- B20 degrees (lead radial)
- C30 degrees (lead radial)
- D5 degrees (lead radial)
Show answer & explanationAnswer & explanation
Correct answer: A. 10 degrees (lead radial)
Standard technique for DME arcs is to lead the turn onto the inbound course by approximately 10 degrees prior to reaching the inbound radial, allowing the aircraft to roll out on course rather than overshoot it.
Why the other options are wrong
- B. 20 degrees would cause the aircraft to roll out well before the arc, cutting inside the course.
- C. 30 degrees is excessive and would significantly shortcut the arc.
- D. 5 degrees is too small a lead and usually results in overshoot at normal approach speeds.
DME Arc Lead Radial
The technique of beginning the turn onto the inbound course approximately 10 degrees prior to reaching the defining radial while flying a DME arc, to compensate for turn radius.
- Standard lead is 10 degrees
- Compensates for aircraft turn radius
- Used at the completion of a DME arc procedure
- Distance is maintained via DME readings along the arc
Memory trick: Lead by 10 to land on the line