Aero-Tips!

A good pilot is always learning -- how many times have you heard this old standard throughout your flying career? There is no truer statement in all of flying (well, with the possible exception of "there are no old, bold pilots.")

Aero-News has called upon the expertise of Thomas P. Turner, master CFI and all-around-good-guy, to bring our readers -- and us -- daily tips to improve our skills as aviators. Some of them, you may have heard before... but for each of us, there will also be something we might never have considered before, or something that didn't "stick" the way it should have the first time we memorized it for the practical test.

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Aero-Tips 11.07.06

It's the little things that can get you...

I was in the right seat of a Beech Baron as my student, a year since last flying, was under the hood inbound for his first practice ILS (Instrument Landing System) approach. Olathe, Kansas' New Century Airport was busy that Sunday afternoon, with traffic using Runway 18 into a light southerly wind. Sandwiched between low clouds and fog to the south and east, and a Presidential TFR (Temporary Flight Restriction) close by to the west, we were in good visual conditions with New Century Tower's permission to fly the ILS Runway 36 opposite the direction of traffic so long as we broke off the approach before the runway threshold. Climbout instructions were to fly heading 270° and maintain VFR.

Like most Barons, this one has a Horizontal Situation Indicator (HIS), a single instrument that combines the heading indicator and navigation display on a single instrument for ease of instrument scan (figure 1, above). The HSI includes four elements vital to understanding a potentially fatal scenario we uncovered:

• The heading card, which in this case automatically aligns itself to offset precession (no need to manually set it to the magnetic compass).
• The course needle that indicates the direction to an identified navigation facility.
• The glideslope indicator that shows the airplane's relationship to a precise descent path to the runway.
• The heading bug, a manually set direction indicator that acts as a reminder of heading to be flown (or, if using the autopilot in heading mode, which way the autopilot should fly).

Figure 2 (below) is a simplification of what the HSI looked like inbound on the ILS. The course needle was centered; my student had swung the heading bug around to 270° as a reminder of the assigned heading for the missed approach. Coaching my student as he flew the approach I kept prompting him that he was above glideslope. He needed to increase his rate of descent slightly to reintercept, but he wasn't responding and the glideslope needle (the orange trapezoid on the side of the HSI) was descending further and further below us. We were nearly at full glideslope deflection when time came to break off the approach because of opposite-direction traffic. I had my student look up briefly to see how close and high we were above the runway.

Here's the gotcha -- looking at the HSI, my student was "seeing" the heading bug he'd placed on 270° as a centered glideslope indicator. On his HSI they're shaped the same, although they're a different color. With the coincidence of a missed approach heading exactly 90 degrees to the left of our inbound course, the heading bug looked just like a centered glideslope indication. My student interpreted it as such when in fact we were high on the approach. I have to admit that it fooled me for a few seconds.

Imagine the possibility for error if he was below glideslope and he made this interpretation. All the NTSB would ever be able to discover is that the airplane descended below glidepath into terrain for unknown reasons.

Many HSIs have two glideslope indicators, one on each side of the HSI... but not all do. This would be a rare HSI setup on an actual approach, but it's not impossible.

Aero-tip of the day: Watch out for the "little things" that can mislead you to an accident. Take a look around your cockpit and see if there are similar "gotchas" in the airplane you fly. 

FMI: Aero-Tips