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I.L.A.F.F.T.: The Glide Slope

A faulty glideslope connection fools a pilot into following the instrument's needle almost into the ground.

Credit: Joel Kimmel
Gemini Sparkle

Key Takeaways:

  • A pilot nearly crashed during an ILS approach when a wiring error, caused by a recent GPS installation, made the HSI's glideslope needle appear centered and functional despite receiving no actual glideslope signal.
  • The pilot unknowingly followed this false vertical guidance, descending dangerously close to trees and narrowly avoiding a collision just above decision height.
  • The incident underscored the lack of a clear glideslope signal validity indicator on the HSI and highlighted the critical importance of cross-referencing instruments, questioning unexpectedly perfect indications, and the value of system redundancy.
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It was 2001, and an IFR-approved panel-mounted GPS had just been installed in my airplane, a Cessna 180. I was anxious to see it in action with its moving map, multitude of functions, and the information it provided. A short 20-minute flight to a nearby airport for breakfast with a friend and some hands-on use of the new equipment was in order.

The weather at the breakfast airport that morning was not VFR because there was a low marine stratus layer. The AWOS reported instrument conditions, with a 300-foot overcast but reasonable visibility of 4 miles below the cloud deck. Because I pride myself by staying instrument current, this would help me stay current.

Alen Hewitt

Alen Hewitt flew U-8s in Vietnam and is a retired electrical engineer who owns a 1966 Cessna 180.

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