What is the normal vibration range during air transport?

• A. 5mm at 7 Hz to 0.05mm at 200 Hz
• B. 1mm at 5 Hz to 0.1mm at 300 Hz
• C. 2mm at 4 Hz to 0.2mm at 150 Hz
• D. 10mm at 1 Hz to 0.5mm at 50 Hz

Answer: (A)

During normal air transport, vibration covers a broad range of frequencies, with larger motions at lower frequencies and much smaller motions as frequency increases. This happens because the aircraft structure tends to move more noticeably at some low-frequency modes, while higher-frequency vibrations are quickly damped and produce only tiny displacements.

The described range—about 5 mm at 7 Hz down to 0.05 mm at 200 Hz—fits that pattern: a relatively sizable movement at a low frequency, tapering off to a very small movement at higher frequencies. This envelope reflects what is typically observed in flight, where occupants and equipment experience a spectrum of vibrations rather than a single constant motion. The other options show either too large a movement at high frequencies or unrealistic limits that don’t align with normal flight vibration characteristics.