Ya Gotta Fly a DME Arc

A DME arc is a curved track at a constant distance around a facility that offers omnidirectional course information and DME, such as a VORTAC, VOR/DME or NDB/DME. This eliminates ILS or LOC DMEs. An arcs radius is 7- 30 NM and is 5-15 NM long, with 10 NM preferred. Thus, arcs can be lengthy and inefficient. The primary area required obstacle clearance is 1000 feet within four NM of the arc along the initial segment, with a 500-foot secondary clearance extending another two NM. In the intermediate segment, the clearance drops to 500 feet.

Fred Simonds

Wednesday, August 15, 2018 at 12:00 AM ET

Verified

Key Takeaways:

DME arcs are challenging curved flight paths at a constant distance around a navigation facility, required for instrument pilot proficiency and typically used as initial approach segments.
Pilots fly DME arcs by maintaining a constant DME distance from the facility, using techniques such as DME monitoring, VOR CDI centering (e.g., "turn-two, twist-two"), or RMI, while constantly adjusting for wind and leading turns to join and exit the arc.
Modern GPS navigators can substitute for DME and assist with flying arcs, including autopilot integration; however, GPS lateral guidance is prohibited on the final approach segment of ILS or other localizer-based approaches.

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Most IPC tasks are routine. But, flying DME arcs is not and it’s no surprise that IPC applicants have more difficulty with them than any other. Perhaps this is why seldom-used skills like DME arcs remain on the books.

The Airman Certification Standards (ACS) does not require that a DME-arc approach be flown: “While the applicant is expected to be able to fly DME arcs, they may be selected for testing only if they are charted and available.” Since the nearest arc approach where I fly is some 50 miles away, flying an arc not on an approach will suffice. On approach or not, the skill is the same.