Relevant Discussion: AIM 5-4-5, 7-1-11, 7-2-1 through 7-2-5, P/C Glossary, FAA-H-8083-16, AC 00-45, AC 91-70, AC 120-28D, Order 7110.65T
Everything Explained: Altimetry Around the World
Key Takeaways:
- Q codes are three-letter telecommunications codes used for altimeter settings: QNH represents local barometric pressure (reading field elevation on the ground), QNE is the standard pressure altitude (29.92 inHg or 1013.2 hPa), and QFE sets the altimeter to zero feet on the ground.
- Pilots typically use QNH below a country's designated transition altitude and switch to QNE at or above it, with a "transition layer" existing between these settings where altimeter adjustments occur (in North America, the transition altitude and level are both 18,000 feet msl).
- International flight operations require pilots to be aware of regional variations in transition altitudes/levels, altimeter units (e.g., inches of mercury vs. hectopascals), and altitude measurements (feet vs. meters), necessitating accurate conversions and adherence to local procedures.
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