Aircraft Performance and Planning
What the exam tests
Aircraft Performance and Planning tests whether you can compute weight and balance, density altitude, and fuel requirements, and then interpret the result. The BGI must teach applicants to use data, not intuition.
Weight and balance
- Moment = weight × arm. CG = total moment ÷ total weight.
- Empty weight, occupants, fuel, and baggage must all be included. Aviation gasoline weighs 6 lb/gal.
- Forward CG increases stall speed and reduces elevator authority; aft CG reduces stability and can make a stall unrecoverable.
Performance and density altitude
- Pressure altitude is indicated altitude set to 29.92 inHg. Density altitude is pressure altitude corrected for nonstandard temperature.
- Rule of thumb: density altitude rises about 120 ft for each 1°C above ISA. ISA at sea level is 15°C and decreases 2°C per 1,000 ft.
- Takeoff and landing distances increase with density altitude, weight, and tailwind; climb performance decreases.
Worked example
Empty weight 1,000 lb at arm 40.0 in; pilot 170 lb at 37.0 in; fuel 40 gal at 48.0 in; baggage 30 lb at 95.0 in. Max gross is 1,600 lb; CG limits are 38.0–46.0 in. Is the loading legal? Reasoning:
- Empty moment: 1,000 × 40.0 = 40,000 lb-in.
- Pilot moment: 170 × 37.0 = 6,290.
- Fuel weight: 40 gal × 6 = 240 lb; moment: 240 × 48.0 = 11,520.
- Baggage moment: 30 × 95.0 = 2,850.
- Total weight: 1,000 + 170 + 240 + 30 = 1,440 lb.
- Total moment: 40,000 + 6,290 + 11,520 + 2,850 = 60,660 lb-in.
- CG: 60,660 ÷ 1,440 = 42.1 in. The weight is below 1,600 lb and the CG is within 38.0–46.0 in, so the loading is legal.
Traps that cost marks
- Treating gallons of fuel as pounds.
- Omitting baggage or occupants from the moment table.
- Using pressure altitude when the chart is labeled density altitude.
- Ignoring a tailwind component in takeoff distance.
- Assuming an aft CG is safer because it feels less nose-heavy.