What is an important consideration when using the VSI?

• A. Calibration accuracy
• B. Wind drift
• C. Lag characteristics
• D. Temperature sensitivity

Answer: (C)

The important thing to understand about the VSI is its lag in signaling vertical speed. The VSI uses a pneumatic mechanism with a calibrated leak to produce a pressure signal that changes as your rate of climb or descent changes. Because of that mechanism, the indication responds more slowly than your actual vertical motion, so the needle trails behind. This delay means you can momentarily see a higher or lower climb rate than you’re actually producing, especially during transitions like leveling off or making a quick pitch change. To fly safely, anticipate this lag and routinely cross-check the VSI with the attitude indicator and what you feel through pitch and power. That way you won’t overreact to a reading that’s not yet reflecting your true vertical speed.