What is the purpose of hermetically sealing an instrument?

• A. To prevent tampering.
• B. To maintain proper function and reliability by securing against water and foreign bodies.
• C. To make it lighter.
• D. To comply with disposal rules.

Answer: (B)

Hermetically sealing creates a completely airtight interior, which protects sensitive avionics from moisture and contaminants. When moisture or dust gets into instruments, humidity can cause corrosion, short circuits, insulation degradation, or condensation that disturbs measurements, all of which undermine reliability. The seal also helps keep out foreign bodies that could interfere with moving parts or delicate sensors, especially under the wide temperature and pressure changes experienced during flight. By maintaining a stable, dry, contaminant-free environment inside, the instrument continues to perform as designed and remains reliable over its service life. While a seal can make tampering harder, that isn’t the primary purpose; the main goal is environmental protection to sustain proper function and reliability. It’s not about reducing weight or meeting disposal rules.