Hot, high, and humid days quietly steal performance from your aircraft — and the exam will ask you to explain why. Enter your field elevation, the temperature, and the altimeter setting to see your pressure altitude and density altitude, plus a plain-English read on what "thin air" really does to lift, climb, and your drone's motors. Understand it here, and the test question answers itself.
Density altitude is pressure altitude corrected for temperature — the altitude your aircraft "feels" like it's flying at. When air is hot, high, or humid, it's thinner, so wings make less lift, props and rotors bite less air, and engines and motors make less power. A drone or plane at a 1,000-ft field on a 100°F afternoon can perform as if it's thousands of feet higher — which is exactly why the ACS wants you to respect it, not just recite it.
| Step | Formula (rule of thumb) |
|---|---|
| Pressure altitude | elevation + (29.92 − altimeter) × 1,000 |
| ISA (standard) temp | 15°C − 2°C per 1,000 ft of pressure altitude |
| Density altitude | pressure altitude + 120 × (OAT − ISA temp in °C) |
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