Weight and Balance: The Preflight Calculation You Can Never Skip

Weight and balance is not optional. It is not a formality. It is a legally required preflight calculation, and exceeding your aircraft's center of gravity limits or maximum gross weight can make your aircraft unflyable — or unrecoverable. I have given weight and balance ground lessons to student pilots, instrument students, and experienced private pilots getting their commercial certificate, and the misconceptions I encounter are the same every time. This guide explains exactly how weight and balance works and how to calculate it correctly.

Why Weight and Balance Matters

Your aircraft is certified to fly within a specific weight range and with the center of gravity (CG) located within defined forward and aft limits. The manufacturer determined these limits through flight testing — they define the edges of the aircraft's certified flight envelope. Operating outside these limits means you are flying an aircraft whose handling characteristics, stability, and stall behavior are unknown and potentially dangerous.

Aft CG is particularly dangerous. When the CG moves too far aft, the aircraft becomes increasingly unstable in pitch. In the extreme case, the elevator may not have enough authority to recover from a stall. Aft-CG accidents are almost always fatal.

Forward CG is more forgiving but still dangerous. A very forward CG requires a large nose-up elevator input to rotate on takeoff and maintain level flight. In some cases there may not be enough elevator authority to flare on landing.

Overweight operations increase stall speed, lengthen takeoff roll, reduce climb performance, and increase structural stress on the airframe. Maximum gross weight limits are structural limits certified through testing — exceeding them is not just illegal, it is genuinely dangerous.

The Three Key Concepts

Weight

Every item in the aircraft has a weight. This includes the aircraft's empty weight (from the weight and balance record in the aircraft documents), pilot, passengers, baggage, and fuel. Fuel weight: aviation gasoline (100LL) weighs 6 pounds per gallon. Jet-A weighs approximately 6.7 pounds per gallon. Never estimate fuel weight — calculate it.

Arm

The arm is the horizontal distance in inches from the aircraft's datum (reference point, usually the firewall or nose) to the item being measured. Arms are positive (aft of datum) or negative (forward of datum). Every item in your aircraft has a specified arm — found in the POH weight and balance section.

Moment

Moment = Weight × Arm. It is measured in pound-inches (lb·in) or pound-feet (lb·ft). The total moment divided by the total weight gives you the CG location in inches from the datum.

Step-by-Step Weight and Balance Calculation

Here's the process for a Cessna 172 with four occupants and full fuel:

1. Find your aircraft's empty weight and empty CG arm from the current weight and balance record (not from the POH — the record in the aircraft documents reflects any modifications or equipment changes since manufacture).
2. Calculate the empty moment: Empty weight × Empty CG arm
3. Add each loaded item: For each passenger, bag, and fuel load, multiply weight by the arm for that station (seats, baggage area, fuel tanks) from the POH
4. Sum all weights — this is your total takeoff weight. Verify it is at or below maximum gross weight.
5. Sum all moments — divide by total weight to get loaded CG
6. Verify CG is within limits — check against the CG envelope in your POH for your total weight
7. Check landing weight — after burning fuel, recalculate CG at landing weight. CG moves as fuel burns depending on the fuel tank location relative to the datum.

Common Weight and Balance Mistakes

• Using estimated passenger weights. Use actual weights. The FAA standard average weights (190 lbs for adult males, 179 lbs for adult females in summer clothing) are for statistical purposes in large transport operations — not for small GA aircraft with a 1,000-pound useful load where 20 pounds matters.
• Forgetting baggage arm locations. Most light aircraft have two baggage areas with different arm values. Check your POH — putting heavy bags in the wrong compartment can push you outside CG limits.
• Not checking the CG envelope. Some aircraft have CG limits that vary with weight. A CG that is acceptable at light weight may be out of limits at maximum gross weight. Always check the envelope, not just the limits.
• Skipping the calculation because the aircraft feels light. The aircraft being lightly loaded does not mean the CG is within limits. Four adults in the back seats and an empty front seat can create an aft CG issue regardless of total weight.