Density Altitude and Aircraft Performance

Air density is what the wing, propeller, and engine actually work with, and three factors thin it out: higher altitude, higher temperature, and higher humidity. Density altitude is simply pressure altitude corrected for temperature — the altitude the airplane behaves as if it were flying at. On a hot day at a high-elevation airport, density altitude can be thousands of feet above the field elevation, so the wing makes less lift, the propeller bites less air, and a normally aspirated engine makes less power. That combination lengthens the takeoff roll and flattens the climb. Takeoff and landing distances also grow with higher weight, a tailwind, an upsloping runway on takeoff, and a soft or contaminated surface, while a headwind shortens them. The prudent pilot treats a hot, high, heavy, downwind takeoff as the worst case and plans generous margins.