How often must Height-Keeping Monitoring be checked?

• A. Every year
• B. Every 2 years or 1000 flight hours per aircraft, whichever is longer
• C. Every 5 years
• D. Monthly

Answer: (B)

Height-keeping monitoring is about keeping altitude reference systems accurate over time, so pilots can rely on correct altitude readings. The checked interval uses both time and usage: every two years or after 1000 flight hours, whichever comes first? Actually whichever is longer. This approach means you perform the check at least every two years, but if the aircraft has accumulated a lot of flight hours, you’ll do it based on hours sooner than the two-year mark. It balances aging effects that happen with time and wear that accrues with flying time. For low usage, you’re still covered by the two-year minimum; for high usage, the hours trigger the maintenance to catch drift before it becomes unsafe.

Other options don’t align with this safety-minded cadence. A yearly or monthly schedule can be unnecessarily frequent for many systems, driving unnecessary maintenance costs, while waiting five years risks uncorrected drift in altitude indications.