How should a pilot interpret a rapidly changing VSI during instrument flight?

• A. It indicates rapid vertical movement (climb or descent) and should be cross-checked with altitude changes.
• B. It indicates airspeed fluctuations.
• C. It indicates engine RPM.
• D. It indicates magnetic variation.

Answer: (A)

The main idea is that the vertical speed indicator shows how fast you’re moving up or down. A rapidly changing VSI means you’re changing altitude quickly in the vertical direction—you're either climbing fast or descending fast. In instrument flying, you’d cross-check that with the altimeter to verify that the altitude is actually changing as indicated. The VSI doesn’t measure airspeed, engine RPM, or magnetic variation, so those indicators won’t be telling you about rapid climbs or dives.