What is the maximum allowable discrepancy in altimeter settings for IFR operations?

In IFR (Instrument Flight Rules) operations, maintaining accurate altitude readings is critical for safety, especially when multiple aircraft operate in close proximity. The maximum allowable discrepancy in altimeter settings is 100 feet. This ensures that all aircraft operating under IFR are following standardized altimeter settings, enhancing the safety of air traffic.

If the altimeter settings between two aircraft differ by more than 100 feet, it may indicate a significant error in one or both aircraft's altimeter calibration or the altimeter setting itself, potentially leading to separation issues and increasing the risk of altitude conflicts. Therefore, maintaining a discrepancy within this limit helps to keep pilots and air traffic controllers aware of altitude changes and promotes safer flight operations.

Understanding this standard is essential for pilots during pre-flight checks and inflight operations to ensure compliance with regulations and to facilitate accurate altitude reporting.