![In today’s glass cockpit world, knowing everything you can about your avionics is as important as knowing how to fly the airplane. [Courtesy: Max Trescott]](https://flyingmag1.b-cdn.net/wp-content/uploads/sites/2/2025/09/FLY0925_3.7-Max-Impact.jpeg?width=1917&height=1444)
Does that APR, or approach mode key, on your autopilot somehow activate a GPS receiver so it can fly an approach? The answer is no, it doesn’t. And if you’re confused about that, you’re not alone.
And is there something in a GPS receiver that must be “activated” at some point before one can fly an approach? Again, the answer is no. You can fly any instrument approach, either via pilot navigation or vectors and never have to “activate the approach.”
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Yet, I often hear pilots say, “Now I have to activate the approach,” when in fact their GPS is already set up correctly for the approach.
What they often do at that point, in a glass cockpit aircraft with Garmin avionics, is push the “PROC” key and choose “ACTIVATE APPROACH.” While that may seem logical, it can totally screw up the programming that was already correctly set to fly an approach. And as I’ll explain in a moment, it’s likely that doing this was the cause of an accident at a local airport.
Many pilots have a false sense that they must activate something in their GPS navigator before they can continue an approach. In my Max Trescott’s GPS and WAAS Instrument Flying Handbook, now out of print, I referred to this as the “myth of activating the approach.” The myth probably stems from the two choices presented, “LOAD” or “ACTIVATE,” when selecting an approach. And that leads many pilots to assume that if they initially choose LOAD instead of ACTIVATE, that they will later need to activate something to fly the approach. Not so.
Here’s the real problem. Many pilots don’t understand what happens when you push the PROC key and choose ACTIVATE APPROACH. But it’s incredibly simple. All it does is instruct your GPS navigator to draw a straight line from the aircraft’s present position to the initial approach fix (IAF) of whatever instrument approach procedure has been selected. In practice, I almost never use that command, as I often start approaches at an intermediate fix (IF), so there’s no value in having the GPS navigator provide course guidance to the IAF.
There’s at least one situation where trying to “activate the approach” can get a pilot into serious trouble. Imagine you’re inside the IAF on a leg of an instrument approach. Everything is looking good, and you’re properly set up for the approach, yet a nagging feeling tells you there’s one more step you need to activate to continue flying it.
To get rid of that feeling, you press the PROC key and select ACTIVATE APPROACH. When you do that, the autopilot will immediately command a 180-degree turn to take you back to the initial approach fix, which is actually behind you. Should you find yourself in this or some other situation involving an automation surprise, disconnect the autopilot and manually fly the airplane.
I always tell clients I fly with that when you’re doing something that can kill you, whether it’s handling rattlesnakes or flying airplanes, you want to know everything you possibly can about the subject. When learning the systems of an airplane and the nuances of its avionics, no detail is too small because you never know which piece of knowledge could help save your life someday.
Here’s how not knowing about the meaning of activating an approach may have killed a pilot.
In January 2003, a 460-hour private pilot, who was issued his instrument rating just 17 days before, was flying a Cirrus SR20 on what was then called the GPS Runway 31 approach into the Reid-Hillview Airport (KRHV) in San Jose, California. The accident occurred shortly after the pilot passed the final approach fix (FAF) while in IMC.
While vectoring the aircraft, the controller attempted to provide what they believed was a helpful method of handling the airplane in the transition to the GPS approach. However, these methods of clearing the pilot for the GPS approach were not in strict accordance with FAA Order 7110.65 and included an intercept angle with the final approach course that was greater than allowed.
The airplane was on a modified downwind and proceeding to the IAF when the controller cleared the pilot to turn toward an intermediate fix between the IAF and FAF. The pilot questioned the clearance, and then acknowledged it, and the airplane turned left toward the FAF, which was directly behind the airplane. The controller noticed that the left turn put the airplane heading toward high terrain and advised the pilot to turn right to go to the intermediate fix. After some additional confusion, the airplane’s track stabilized on the approach course after passing the intermediate fix.
As the airplane passed the FAF, the controller told the pilot to contact the tower but gave him the frequency for the wrong airport. The pilot questioned the controller, who insisted the frequency was correct. The pilot then contacted the second airport tower and was told he was on the wrong frequency. Almost one minute elapsed between the pilot’s acknowledgment of the erroneous frequency and his initial contact to the correct tower. During this period, the airplane’s heading diverged approximately 90 degrees from the published final approach course toward rising terrain and the accident site.
The probable cause included the pilot’s failure to maintain the course for the published approach procedure due to his diverted attention. The distraction responsible for the pilot’s diverted attention was the erroneous frequency assignment provided by ATC and the resultant task overload induced by this problem and the confusion surrounding the ATC clearances to get established on the final approach course, which likely involved repeated reprogramming of the navigation system.
What the National Transportation Safety Board (NTSB) report doesn’t say is that some CFIs, familiar with the aircraft type and avionics, have speculated that the pilot erroneously “activated the approach.” This would have caused the aircraft to turn 180 degrees to return to the IAF, explaining why the aircraft turned 90 degrees prior to impacting terrain.
In today’s glass cockpit world, knowing everything you can about your avionics is as important as knowing how to fly the airplane.
This column first appeared in the September Issue 962 of the FLYING print edition.
