What is an initial step a pilot must take if they encounter fluctuating altitude indications during their approach?

When a pilot encounters fluctuating altitude indications during an approach, the priority is to ensure safety and maintain situational awareness. Notifying Air Traffic Control (ATC) immediately is crucial because they can provide assistance, including radar guidance and alerting other aircraft in the vicinity. Effective communication with ATC allows for a coordinated and responsive approach, which is particularly important in fluctuating altitude scenarios where the pilot's own instruments may be unreliable.

Reverting to standard weather minimums or flying the approach to minimums can be dangerous if the altitude readings are not accurate, as these actions depend on the pilot’s understanding of reliable altitude measurements. Engaging the autopilot may not be advisable if the pilot doubts the accuracy of the altitude indications, as autopilot systems might also react to erroneous data.

Thus, notifying ATC is a fundamental step in managing the situation safely and effectively. It helps ensure that the pilot is supported and can make informed decisions based on updated information from air traffic services.