Welcome Guest. Sign in or Signup

3 Answers

Problem with IFR GPS Approaches

Asked by: 1822 views Instrument Rating

Hi everyone,

I took my IFR checkride a couple weeks ago and unfortunately ran into issues with the GPS approach. The approach was the last one of the flight. For the previous two approaches (an ILS and a Localizer partial panel) I had the approach loaded into my airplane's KLN 94 and had the moving map up for situational awareness. When I flew the hold, I put the GPS into OBS mode as I approached the holding fix, set Nav 1 to the inbound course of the hold, and flew the hold by tracking the CDI for the inbound course. Simple enough.

The problem was when I asked for the GPS and approach vectored me out of the hold. I set up the approach in the GPS but forgot to switch back from OBS to LEG mode. I got to the IAF but of course, the GPS didn't sequence onward to the IF. At the time I had no idea why this was happening, and I asked approach if I could get vectors to try the approach again. The examiner was ok with this, but since I was still in OBS, the GPS again wouldn't sequence from the IAF to the IF. At this point I simply told the examiner I had no idea what was happending-he had my take the hood off and fly back VFR, I knew that was it. 

When we got back to his office he explained that we had been in OBS, and I couldn't believe I hadn't caught it. He also wanted to do the partial panel approach again, and so I met with my instructor a few days later to fly the same localizer partial panel, followed by the hold, then the GPS for a circle to land. I was fairly confident after the checkride I wouldn't make the same mistake with OBS again.

The trouble is I did. In fact I've flown three flights with my CFI since the checkride and I've failed to take the GPS out of OBS in the hold two out of those three times. I honestly can't explain it. My instructor has told me that my flying otherwise is fine-I'm good with staying ahead of the airplane, running through checklists, briefing approaches, as well as my useage of the KLN 94. For some reason my brain has failed 3 of the 4 previous times to process the fact that I shouldn't be in OBS. On my most recent flight, tonight, we asked for the GPS while in the hold and approach asked us to proceed directly to the IAF. I felt very rushed-I set up the approach quickly in the GPS, scrolled to the IAF, Direct->Enter etc, and at that point felt pleased that I had gotten everything set up in a timely manner and was on my way to the IAF. After about 20 seconds I noticed I was still in OBS! I was pissed beyond belief (I was able to calm down quickly and keep flying the airplane) but I just don't know what I can do differently. After my checkride I add a note about OBS/LEG to my personal checklist for approach briefing. I'm finding that I can't look over every checklist item during flight, just cause of how fast everything moves, and so the last couple times I've just flat out missed that item on my checklist.

Have you (or a student of yours) ever been in a similar situation, be it in IFR or VFR, where one little thing messes up your routine every time (and it's always the same thing)? How did you cope with such a situation? What are your thoughts for how I might approach this problem? 

Any thoughts/suggestions/comments would be very welcome and appreciated.




3 Answers

  1. Mark Kolber on Mar 06, 2013

    This type of think can be tough one. Here’s my take. It will be long since it’s mostly explanation. Hopefully it will help a little. For context, to me, IFR flight is about 10% about flying the airplane but about 90% about the procedures involved in flying within a system. When I do instrument training, my focus tends to be on the pilot developing internal procedures to assist in coping with the external ones.

    You’ve no doubt learned about “staying ahead of the airplane.” Your CFII may have taught you the so-called “5 Ts” (or 6 or 8 or 12) as a mnemonic reminder for the tasks that need to be, if not accomplished, at least = considered = every time you cross a fix. People who know me may laugh that I’m mentioning the T’s because I’m not a fan of mnemonics. But think about what the “Ts” are really trying to tell you in terms of staying ahead of the airplane the development of person SOPs that allow you to do so.

    To me, “staying ahead of the airplane” is about anticipating the next thing that needs to be done, well before you need to do it. For example, if you’re crossing a fix and then thinking about what to do, it’s too late. You’re playing catch-up – trying to determine what you were supporst to have done while already working on the next step. An error, a missed frequency change, a missed spin of an OBS, are all going to be much harder to detect and likely to go unnoticed.

    Notice that you said, “I put the GPS into OBS mode =as I approached= the holding fix.” Not after crossing it. Before. And then, referring to flying the hold, “simple enough.” Anticipation of what was next. And the flying itself is simple.

    Once you enter that hold and get stabilized in the pattern, what are you doing? Probably not much. If you’re going to be in the hold multiple legs, you’re mind is probably pretty well attuned to the turns, the timing and the courses. The only thing left to do is waity for leaving the hold. That’s the time to be thinking, “Hmmm. What are the tasks I will need to accomplish when ATC releases me from the hold? Might be instructions to execute the approach from here. Might be vectors coming around again. What do I need to do in wither case?”

    One of those tasks will be to switch back to leg mode. Another might be to switch to change the NAV source to the localizer. Whatever those tasks are, thinking about them in advance sets a trigger in your brain to accomplish them at the appropriate time. And if you get into the habit of doing that on a regular basis, especially when the procedure is “simple,” these types of errors are less likely to occur.

    That’s a very long-winded way of saying, create personal standard operating procedures that allow you to anticipate what’s next and follow them.


    0 Votes Thumb up 0 Votes Thumb down 0 Votes

  2. John D. Collins on Mar 06, 2013

    First, avoid the use of OBS mode on an approach unless you have a need for it. The only time you have a need for using OBS mode on the approach is when a course reversal is required, either because of a PT or a HILPT.

    When you are flying the course reversal you will need to set your HSI/CDI course pointer to the inbound course to the fix. As soon as you have set the OBS to the inbound course, immediately use the OBS button to switch off OBS mode. If you are ahead of the airplane, you can do this while you are still outbound in the PT or hold. Consider setting the inbound course and turning off OBS mode as a single action and make it a habit. The only time this won’t work is if you are remaining in the hold and doing additional circuits. In this case, you need to turn off OBS mode on the last circuit when you plan on sequencing inbound on the approach.

    Each GPS has its own interface peculiarities that have to be learned. In most GPS installations, the GPS itself is not located in the pilot’s primary field of view and annunciators are required to be installed directly in the pilot’s primary field of view so it is more difficult to miss needed indications. Unfortunately, for the KLN94, it doesn’t have an annunciator output for Leg/OBS mode, so you can only obtain this information by swiveling your head and getting it from the KLN94 itself. This is a human factors deficiency in my view, but it is what it is and you have to learn to deal with it.

    0 Votes Thumb up 0 Votes Thumb down 0 Votes

  3. Jeremy H on Mar 07, 2013

    What helped for me (from the perspective of someone on a GNS 430) was always being clear about which is your primary navigation source. You mention using the KLN as “situation awareness” but if you are flying a GPS approach, it’s primary navigation. If that panel fails, you can’t fly the approach. When you’re in a hold based on a radial, the GPS is only situational, it’s a nice to have but your primary is radio. A couple times, my instructor would cover the GPS panel during a hold during a GPS approach to ingrain that we were using a navaid. When you get into situations where you go from vectors to a navaid to GPS pretty quick, you want to be sure that you’re clear about primary navigation (especially on a GPS approach because you’ll be descending into terrain) because you may not get enough time to get a backup form of navigation plugged in.

    Another thing that might help is about the requirements that you need on a particular segment. Mentally saying, “I’m on a GPS approach, that means I check for RAIM” verus “I’m on a VOR and I check the radial, TO/FROM flag coming alive, and can even check for station ID on the NAV radio” The great thing about having different types of equipment is that it allows more flexibility in flying. You do have to be clear about which system that you are using.

    Maybe practicing a different approach at a different airport so that you also don’t memorize the mechanics on that particular approach would help too?

    0 Votes Thumb up 0 Votes Thumb down 0 Votes

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.