How to Eliminate Approach Key Confusion for Pilots

In September, I talked about what I call the myth of activating the approach. Many pilots seem to feel they need to activate something in their GPS to fly an approach.

As I pointed out, I often hear pilots say, “Now I have to activate the approach,” when in fact their GPS is already set up correctly for it. If you’re under that impression, please go back and read that column in FLYING Magazine Issue 962.

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A related subject is confusion over the purpose of an autopilot’s APR, or approach, key. My friend Jim Pitman, who’s an airline pilot and DPE, recently sent me the following email: 

“I’m finding that most instrument pilots and flight instructors think the APR key has something to do with waypoint sequencing and ensuring a GPS approach is active. They don’t understand that the APR key is for the flight director/autopilot and has nothing to do with activating a GPS approach. There’s also a lot of confusion about what it means for a GPS approach to be ‘active.’ I’m working on putting together some slides with screenshots. Your podcast would be a good place to have this discussion. What do you think?”

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I receive lots of pitches from people interested in being on the podcast, but few make it onto the show. The worst pitch I ever received simply said, “I want to be on your podcast.” There was no indication of what expertise he had, or what value he could bring to listeners, just an expression of what he wanted. I still know nothing about that person except that he clearly had no experience working in sales.

Pitman’s pitch was a pleasant exception. I wrote back: “I agree. This is a very widespread misconception. I see it all the time.” And then we scheduled a time for him to be on the show.

Part of the confusion about the APR key is that pilots often confuse the functions of their GPS navigator with their autopilot. I suspect that modern glass cockpits add to that confusion. Previously, instrument panels were a collection of stand-alone units. So, it was easy to see that one box, for example, was a GPS, and another box was an autopilot. The keys associated with each box were on that box, so there was never any confusion as to what function they performed. 

But with glass cockpits we don’t always have a strong association between some of the keys and units they control. That’s because the stand-alone boxes we used to see are now LRUs, or line replaceable units, hidden from sight, and they have no keys. Instead, the keys for each LRU sit together on a common bezel, so it’s harder to tell which ones go with which units.

Jim’s approach to explaining the use of the APR key was one of apples and oranges. In his analogy, apples represented the GPS navigator, while oranges represented the Automatic Flight Control System (AFCS), better known as the autopilot. The APR/approach key was one of the oranges. It’s associated with the AFCS, so it has nothing to do with the GPS. It has no role in whether an instrument approach in a GPS navigator is “active.”

In the prior century, when we had stand-alone avionics boxes and autopilots working so poorly that many pilots never used them, the distinctions between the autopilot NAV and APR key were relatively clear. The NAV key made an autopilot track a navigational signal, and the APR key did the same thing, plus it could also track a glideslope. 

In addition, people often said the APR key provided more sensitivity for the left/right guidance of the lateral signal than the NAV key. That was probably true then, but it doesn’t appear to be the case with modern glass cockpit aircraft. In newer airplanes, the NAV key appears to track a GPS signal just as well as the APR key. If there’s still an advantage when tracking a VOR or ILS, I haven’t seen it. 

Let’s talk about the apples, or GPS, for a moment. Jim’s approach to explaining to pilots when an instrument approach is active was similar to mine. In Garmin avionics, simply open the flight plan and look at the lines below the title of the approach you’ve loaded. If you see a magenta arrow pointing at one of the lines, or you see a magenta U-turn arrow to the left of two of the lines, sequencing of the approach is set to occur, and there’s nothing further you need to do to “activate” the approach.

Getting the flight plan in either of those states is simple. If you’re cleared direct to one of the fixes on the approach, and you use the Direct-To key to go to that fix, you’ll see a magenta arrow to the left of the fix. Or if you activate any leg on the approach, you’ll see a magenta U-turn arrow next to the waypoints that define that leg. In either case, life is good, and the approach will sequence properly. 

If you’re flying the approach by hand, there’s nothing more you need to do. But if you’re using the autopilot, you will need to push either the NAV key or APR key to track the approach. If ATC initially tells you to “join” or “intercept” the final approach course, push the NAV key. 

You need to do that because you haven’t been cleared for the approach and aren’t yet permitted to descend. Later, when you’re cleared for the approach, push the APR key, which will allow you to couple to the approach’s glideslope or glide path so you can descend. 

A good rule of thumb is to push the APR key whenever you hear the words “cleared for the approach.” For nonprecision approaches with no vertical guidance, you never have to push the APR key. Since there’s no vertical guidance, pushing the NAV key will suffice.

Overall, it’s simple. GPS activation is apples, and APR engagement is oranges. Good pilots know the difference. 

This column first appeared in the November Issue 964 of the FLYING print edition.