Even though the ILS is still the gold standard for instrument approaches, it has an Achilles heel that catches even the professionals off guard. Don’t let it happen to you.
Handling ILS anomalies
Our CRJ-200 was sliding down through an overcast layer, following the glideslope to Runway 28 at Chicago OHare. Everything was normal, just like it always is. My airline job means I make this approach a couple of times a week.
Key Takeaways:
- ILS glideslope signals are susceptible to sudden fluctuations caused by ground traffic (aircraft, vehicles) blocking the antenna's line-of-sight, which can lead to wild autopilot responses and potential control issues during coupled approaches.
- Although ILS critical areas are designated to prevent such interference, ATC protection is limited to specific low-visibility conditions or explicit pilot requests, leaving these areas vulnerable during many routine approaches, particularly when control towers are closed.
- Pilots should be prepared for glideslope fluctuations by being ready to disengage the autopilot, manually maintain the required vertical speed using charts, and consider a localizer-only approach or a missed approach if signal integrity is compromised.
- Pilots on the ground, especially at uncontrolled airports, must be mindful of ILS critical areas and avoid crossing them when an aircraft may be on an instrument approach to prevent signal interference.
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