Height-Keeping Monitoring must be checked every 2 years or 1000 flight hours per aircraft, whichever is longer. Which option best expresses this rule?

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

Answer: (C)

The idea being tested is how to schedule a maintenance check when two separate limits exist: calendar time and accumulated flight hours. The rule uses the longer of the two intervals, so you schedule the check at the later date between the 2-year mark and reaching 1000 flight hours. This ensures you don’t violate either requirement.

For example, if you hit 1000 flight hours in 1.5 years, the later deadline is 2 years, so the check should be done by the 2-year point. If you reach 1000 hours after more than 2 years, say at 2.5 years, then the check would occur at 2.5 years because that’s the later threshold. So you’re always waiting for the longer of the two, which is exactly what this expression conveys.

The other options fail because they rely on only one metric or ignore one of the limits, which could let you miss a requirement: using only every 2 years ignores hours, using only every 1000 hours ignores calendar time, and a fixed 5-year interval doesn’t reflect either limit.