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 interfering with critical areas, which can lead to unpredictable autopilot reactions.
- ATC protection of ILS critical areas is limited to specific low-weather conditions (below 800 ft ceiling or 2 miles visibility), making approaches vulnerable to interference in better weather or at uncontrolled airports.
- Pilots must be prepared to manage glideslope fluctuations by disengaging the autopilot, manually maintaining the glidepath (e.g., using known vertical speed), or opting for a missed approach if signal integrity is compromised.
- Pilots on the ground should also be aware of ILS critical areas, especially at uncontrolled fields, and avoid blocking them if an aircraft is on approach to prevent signal disruption.
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