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June 1, 1993
By Bruce Landsberg
Nobody likes to miss an instrument approach. It's taken by some pilots as a slur on their ancestry — an attitude that can result in their being brought back on their shields. Others simply continue a botched effort, unaware of the peril. Either way, the message for all of us is to pay particular attention while in the approach phase, lest we miss a crucial sign. Statistics from the AOPA Air Safety Foundation's Emil Buehler Center for Aviation Safety confirm that the leading cause of IFR approach accidents is improper IFR procedure. That covers a multitude of sins, but let's focus on an area that applies to every instrument pilot — recognizing when a missed approach is needed. We'll be even more specific by looking at CDI deflection.
Two episodes involving instrument approaches to the same airport, in this case, Frederick (Maryland) Municipal, show that some pilots may have only a passing acquaintance with the final approach course in actual instrument conditions. In the first episode, a pilot was given a transition from nearby Westminster VOR to intercept the localizer to Frederick's Runway 23. The transition route on this particular approach is about 12 miles from the VOR to localizer intercept, so it's possible the pilot got to thinking about other things and failed to notice the localizer needle sliding across the scale. The needle had obviously been pegged for more than a few seconds when, fortunately, one of the IFR system's checks and balances worked.
ATC noticed the problem first, although radar service had been terminated. "N12345, I show you 5 miles northwest of the airport. Turn left immediately to 100 degrees and re-intercept the localizer. Everybody else, please listen carefully for your call sign, and don't call me for the moment." N12345 acknowledged and proceeded back toward safety, away from the mountainous terrain that lay in its path. This approach is not normally monitored by radar, and it was fortuitous that the pilot had not descended below radar coverage. Others have not been so lucky — more on that in a moment.
The three of us following N12345 wound up holding at the VOR while he completed his approach. However, our challenges were minor compared to the controller, who had to reseparate much of his sector in a hurry. The inconvenience would have been much greater had N12345 disappeared without canceling his IFR flight plan.
Episode two: A 120-hour private pilot with her 1,300-hour CFII had just returned after two hours of multiple approaches and a short cross country. The instructor is a very conscientious young man who is hoping for an airline career and was obviously interested in doing things by the book. His attitude was correct, but the procedure was flawed.
The weather was about 1,200 overcast with 4 miles in fog and light rain — perfect for instrument training in a Cessna 172. The student was having some difficulty in tracking toward the on-airport VOR at Frederick, possibly due to strong winds at 3,000 feet. The controller terminated radar coverage, cleared the flight for the ILS 23 approach, and told them to report procedure turn inbound. To track outbound to the final approach fix, the outer marker, either the localizer or a VOR radial could be used.
A rapidly evolving error chain is something to behold when you can dissect it in detail on the ground afterward. The VOR needle had a full- scale deflection when the to/from flag reversed, and the flight turned outbound to follow the localizer. This is not too unusual, because the needles are sensitive close to the station. Crossing the middle marker, and distracted by the localizer not being centered, the crew started timing for the procedure turn, thinking they were at the outer marker. They remained at 3,000 feet throughout the procedure turn and crossed the localizer momentarily, now headed inbound. The localizer needle went to a full-scale deflection. The glideslope needle properly showed a full down deflection because they were about 1,000 feet above the glideslope over the outer marker.
At this point, the student felt that something wasn't right, and the instructor decided that the CDI and glideslope were malfunctioning. The instructor's comments were revealing. "I was certain that the instrument was wrong and decided that it was safe to descend since I knew we had visual conditions just underneath us. I would never have done that if the weather was low." They descended and became visual, but the airport was nowhere in sight. Recognizing that the approach was now beyond salvaging, they climbed back into radar contact, where the controller showed the 172 to be south of the airport — just where it should have been had they followed the proper path and executed the missed approach. The subsequent approach went perfectly with radar vectors to the localizer, proving that the gremlins the instructor thought had inhabited the ILS earlier had gone off to haunt someone else.
Several years ago, a similar situation, involving a brand-new instrument pilot at Frederick, resulted in a fatal accident on the same hills that N12345 had a close encounter with. Radar service had been terminated, and the flight was cleared for approach and a change to advisory frequency. A different terminal radar was able to track the aircraft, and it was obvious from the meanderings replayed on the radar tapes that the pilot was disoriented. Inside the cockpit, the VOR and localizer needles would have been fully deflected. The way to safety was to climb, notify ATC, and go for a missed approach. He didn't.
The common theme that comes through is a failure to recognize when things aren't going right and to start the missed approach as soon as there is uncertainty, especially when confirmed by instrument indications. Everyone muffs an approach periodically, but the survivors react early and resolve to sharpen up. Unlike the instructor above, the key is to trust the instruments unless you have positive confirmation that there is a malfunction. Because there is usually not time close to the ground to sort these things out, the prudent action is to climb and consider that human error is more likely than instrument error.
Procedurally, consider that if the localizer or glideslope needles peg, it's time to call it quits rather than continue with a bad approach. In training, we must train as if the weather were really down on the deck and handle the aircraft accordingly. One cannot learn to swim by keeping one toe planted on the bottom of the pool, and in flying IFR, it's "sink or swim." Fly procedurally and accept the inconvenience when the needles indicate it's time to miss (and consider going back for more training).
See also the index of "Safety Pilot" articles, organized by subject. Bruce Landsberg is executive director of the AOPA Air Safety Foundation.
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