Overlay Approaches

Lets connect some dots. In 1969, NARCO (now defunct) introduced the CLC-60 VORTAC Offset Control Panel that allowed navigation to a phantom fix defined as a distance and direction (rho-theta) from an existing VORTAC. It was touted as the first RNAV system. In the 80s, Bendix/Kings KNS-80 Integrated Navigation System might be considered the first practical RNAV navigator (it had VOR, LOC, DME, RNAV, and GS). Like the CLC-60, it could electronically move a VORTAC and was IFR certified.

lbencini-tibo

Sunday, February 17, 2019 at 12:00 AM ET

Verified

Key Takeaways:

While approach chart titles indicate required equipment for the final approach segment (FAS), IFR GPS has long been acceptable for substituting DME or ADF in other approach segments.
Recent regulatory updates, specifically in the AIM and avionics AFM supplements (e.g., Garmin GTN), now permit using IFR GPS for lateral guidance on the FAS of VOR or NDB approaches.
A crucial condition for using GPS on the final approach segment of a VOR/NDB approach is that the underlying conventional NAVAID must remain operational and be actively monitored for final course alignment.
Practically, this offers more precise navigation than raw VOR/NDB; however, dedicated RNAV (GPS) approaches are often preferred for offering a glideslope, making this feature most useful at airports without standalone RNAV options.

See a mistake? Contact us.

During an instrument proficiency check, or for that matter an instrument check ride, a common question is, “What does the title of an approach chart indicate? For Example: LOC/DME RWY 18 or VOR RWY 20.” And a follow-up question, “What does ‘ADF Required’ on an approach chart imply (not in the title)?”

Of course, we all know the answers to the questions. Right? The title of the approach indicates what equipment is required to fly the final approach segment (FAS).