What’s 160 feet worth on a close instrument approach? The flexibility to descend to 436 feet agl instead of 596 feet agl on a published procedure could be the difference between a quick landing and a lengthy missed approach, followed by a diversion.
Many instrument approaches afford pilots ways to cash in on such an altitude reduction—but often, at a cost.
The straight-in VOR Runway 6 approach to Tennessee’s Tullahoma Regional Airport came with two sets of minimums, as did the circling variations of the procedure using the now-inoperative navaid. Let's use the approach to build a hypothetical example.
What’s the cost in going for the lower minimums? Increased workload for the pilot, who could use the lower minimums by identifying CEGKA intersection on the final approach course. You are at CEGKA when you cross the 149-degree radial from the Shelbyville VOR-DME as you fly inbound on the final approach course defined by the Tullahoma terminal VOR’s 248-degree radial. A bit of fine print on the approach plate notes that dual VOR receivers are required to fly the approach with CEGKA minimums.
On many procedures there is a more convenient way to identify crossing radials simply as a DME fix along the final approach course. No setting a second nav radio to a second VOR frequency, identifying it, dialing in the crossing radial—would you set that radial, or its reciprocal in your omnibearing selector?—and visualizing its relative position as you fly the course and manage the descent.
That option did not exist on this procedure, so the visualization exercise was well worth some ground review before launching on a flight that might require using the procedure or a similar approach to Runway 24. No, there is no ILS approach to the airport.
So how would your two nav radios be set up when a full VOR approach is commenced outbound from the initial approach fix at the Tullahoma VOR? How many of the “five T’s” (turn, time, twist, throttle, and talk is one rendition of them) would have been employed when starting the procedure turn? Once established inbound, would the crossing radial deflect the course deviation indicator on your No. 2 nav left or right?