CDI flags
5 min read

Election day 2018. Standing in line to vote that morning, I looked up at the thick overcast layer and thought “IFR flying is going to be… interesting today.” Not having much actual IMC time, it’s always a little nerve-wracking for an instrument student to fly IMC. Nevertheless, the weather started cooperating, and by that afternoon when I was ready to fly, the ceilings were lifted all the way to broken at 25,000 ft. with light winds. Picture perfect VFR – only to be “obscured” by necessity to wear foggles to fly under simulated instrument conditions.

CDI flags

Why are those flags showing up?

I’m at the point in my instrument training where my instructor is backing off the constant helpful hints and cues that he would normally be dropping as we fly along. This allows me to make some small mistakes in order to recognize them, correct them, and learn from them. We’d set up our GPS to fly from KPDK to KPUJ to perform the ILS/LOC 31 approach and then onto KRYY for the LOC 27 approach. Flying along, everything was going smoothly, heading and altitude right on the money. As I was vectored in for the ILS, things started to go sideways. As I turned on the approach path, I noticed my CDI #1 needles had the barber pole flags. “Hmm… ok… no big deal,” I thought. “I won’t pick up the glideslope until I reach the final approach fix.”

I continued flying the approach past the FAF. No glideslope. Something was wrong. This was when my instructor asked, “what’s going on?” I told him that I’d passed the FAF, but still had no glideslope intercept or localizer needle movement. Still had the barber poles. I glanced over to my GPS and saw the problem: the CDI was set to GPS and not VLOC.

If this were the checkride, I might’ve just busted it. (Hence the reason some instructors call that CDI button the “$500 button.”) I hit the CDI button to switch to VLOC. Nada. At this point I was really confused, but still flying the airplane, and everything was stable. I hit the knob to switch over to my NAV 1 frequencies. And that’s where I found my issue: the ILS frequency was in the standby for NAV 1.

As soon as I switched it to active, the CDI needles came alive and started dancing. I was on the localizer, but had reached full deflection on glideslope. At my instructor’s urging, I executed the missed approach procedure. As we climbed out, he told me to take off my foggles and look at where the airport was compared to where I was while on the approach. It was a full 2000 ft below us. No way I would’ve ever made that.

As we continued climb out to the hold, we did a quick review of what went wrong:

  1. As soon as I was given vectors to final, I needed to go into the PROC page on the GPS and hit “activate vectors to final.”
  2. Even though I briefed my approach plate, I didn’t fully brief it by double-checking my ILS frequency was active and identifying it in the NAV radio. Instrument flying 101.
  3. I also didn’t check that my CDI was on VLOC rather than GPS.

I was flying an ILS approach like it was a GPS approach. I was also too reliant on the technology without double-checking the input I had given it. Garbage in, garbage out.

LOC 27 plate

Watch the final approach fix and the step-down fix.

On to the next approach at KRYY, the LOC 27 approach, it had already been set up in the GPS. Having quickly learned from the last approach, I verified that the CDI was set to VLOC, my localizer frequency was loaded into the active on my NAV 1, and I’d properly identified the localizer. Again, we received vectors to final to intercept the localizer. OK, good to go. Needles were centered, everything was looking good. I was shifting my scan from the CDI to the GPS to ensure my trend vectors were on point and I was correcting for wind. I was at 3000 ft, which was the initial altitude for the approach, and waiting to cross the FAF so I could descend down to the next stepdown altitude of 1700 ft at the CUMAV intersection. So, I kept an eye on the GPS.

Unbeknownst to me, I’d already crossed the FAF and I hadn’t started descending. My instructor chimed in, again asking what was going on. A closer look at the GPS revealed that instead of thinking I was 3 NM from the FAF, I was now a little more than 2 NM from the stepdown fix of CUMAV and still at 3000 ft. Losing 1300 ft in than distance in a Cessna 172? Not entirely impossible or dangerous, but also not the most comfortable way to do a smooth approach. My instructor commented that it can be done, safely, so I initiated the descent. One thousand feet per minute, here we go. At this point, I’d recovered and continued the approach normally.

In review, my lesson learned here was while technology like the Garmin GPS, ADS-B, ForeFlight, etc. are awesome tools and make single-engine IFR flying easier, we always need to double-check what’s going on and how things are input into those systems.

And always remember to first and foremost – fly the airplane.

I can tell you, next time I fly an approach, I’ll be doing a secondary check to make sure my technology is telling me exactly what I need to make a safe flight en route and approach whether it’s in amazing VFR weather or when it really counts: when the weather is IMC down to minimums.

Editor’s Note: This article is from our series called “I Can’t Believe I Did That,” where pilots ‘fess up about mistakes they’ve made but lived to tell about. If you have a story to tell, email us at: [email protected]

Beau Harper
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4 replies
  1. LS
    LS says:

    I have to laugh. Went on a IFR practice yesterday in Montana and did the EXACT same thing! I will never forget to check the CDI and active NAV again.

  2. George Haeh
    George Haeh says:

    Hard to do that in ye good days before GPS. Fly to the beacon, do a procedure turn and watch the needles on the way back.

    “If you want to screw up big time, use a computer” applies.

    • Mark Hathaway
      Mark Hathaway says:

      As a former computer programmer my tendency is to say the software (instrument in this case) failed the pilot in some way. Yes, it was his responsibility to set things properly, but somehow after he had flown past the checkpoint it hadn’t told him and didn’t indicate that.

      Not all errors are the pilot’s. Some are created by the rules creators and the procedures definers and the software design.

  3. Suresh Kumar Bista
    Suresh Kumar Bista says:

    Many years earlier in Nepal, a Fokker F -27 of Royal Nepal Airline was on an ILS approach to New Delhi in India. Weather at the time of approach was IMC and moderate rain. Three pilots were in the cockpit. One was an instructor checking out the crew for flight release on Kathmandu Delhi sector. He was not seated but standing. A deviation from SOP protocol.

    Aircraft was fully configured as they began the approach. Unfortunately, there was a RED FLAG on the VOR/ILS instrument which all three pilots fail to notice. They believed they were perfectly set up for the approach and continued with the descent. A few moments later, the Fokker F-27 hit electric poles and almost crashed on a wet rice field. The instructor was killed in that incident as he was standing. Some injuries to passengers and significant damage to the aircraft that was later declared beyond recovery.

    When I was doing my Instrument Rating in Canada, during a hold or setting up for approach, my instructor always told me to remember the Four Tees: ” time, turn, tune, throttle, “. On a instrument check ride too, whenever we tuned into a VOR, ILS or NDB, it was mandatory to tune and identify the station. Otherwise, we would fail the check ride. These simple but life saving flying basics are applicable to whether we a Cessna 150 or a Boeing 747.
    Do your checks. Double check.
    Happy Landings !!

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