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 complex, curved flight paths flown at a constant distance from a navigation facility, posing a significant challenge for IFR pilots, particularly during IPCs, due to their infrequent use.
Mastering DME arcs requires precise techniques for joining the arc (leading the turn from a radial), maintaining the arc (keeping constant DME and adjusting for wind, often with VOR CDI or RMI), and exiting the arc (using lead radials or leading turns to intercept the final approach course).
While IFR GPS navigators can substitute for DME and automate much of the arc navigation, pilots must understand their limitations, especially that GPS is not permitted for lateral guidance on the final approach segment of localizer-based approaches.

See a mistake? Contact us.

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.