Aircraft weight & balance: the essential pilot guide

Weight and balance is not a paperwork exercise — it is a critical safety calculation. An aircraft loaded outside its approved CG envelope or above maximum gross weight may exhibit dangerous flight characteristics including inability to rotate on takeoff, insufficient elevator authority to flare for landing, unrecoverable stall behavior, or structural failure during maneuvering.

The regulations are clear: 14 CFR 91.9 requires the PIC to comply with the operating limitations in the approved POH/AFM, which include weight and CG limits. 14 CFR 91.103 requires the PIC to become familiar with all available information concerning that flight, specifically including "runway lengths at airports of intended use" and "aircraft performance under expected values of airport elevation and runway slope, aircraft gross weight, wind, and temperature."

Accident investigation records show a consistent pattern: overloaded aircraft that could not climb, aft-CG conditions that resulted in loss of control, and pilots who assumed "it was fine last time" without recalculating for different passengers, fuel, and baggage. Every flight is different. Every flight needs a current W&B calculation.

Understanding W&B starts with precise definitions. These terms have specific meanings in aviation that differ from everyday usage:

• Datum: An imaginary vertical reference plane from which all horizontal distances (arms) are measured. The manufacturer sets the datum — it may be at the firewall, the nose of the aircraft, or some other reference point. All measurements are relative to this point.
• Arm (station): The horizontal distance in inches from the datum to the center of gravity of an item. Arms aft of the datum are positive; arms forward of the datum are negative.
• Moment: The product of weight multiplied by arm (Weight x Arm = Moment). Moments are expressed in pound-inches and represent the rotational tendency of each item about the datum.
• Empty weight:The weight of the aircraft including unusable fuel, full operating fluids, and fixed equipment. Found on the aircraft's weight and balance data sheet (maintained as part of the aircraft records).
• Useful load: Maximum gross weight minus empty weight. This is the total weight available for fuel, pilot, passengers, and baggage.
• Maximum gross weight: The maximum allowable total weight of the loaded aircraft. May have different values for takeoff, landing, and ramp weight.
• Center of gravity (CG): The point at which the aircraft would balance if suspended. Calculated by dividing total moment by total weight (CG = Total Moment / Total Weight).

The W&B calculation follows a straightforward process. Here is the standard tabular method used for most general aviation aircraft:

Step 1:Record the aircraft empty weight and empty weight CG (or moment) from the aircraft's weight and balance data sheet. This document is updated after any modification or equipment change and lives with the aircraft records.

Step 2: List each item being loaded — pilot, front passenger, rear passengers, baggage in each compartment, and fuel. Record the weight of each item and its arm (from the POH loading diagram).

Step 3: Calculate the moment for each item (Weight x Arm). Some POH tables provide moments directly based on weight, eliminating the multiplication step.

Step 4: Sum all weights to get total weight. Sum all moments to get total moment. Divide total moment by total weight to find the loaded CG position.

Step 5: Verify that total weight does not exceed maximum gross weight AND that the CG falls within the approved envelope for that weight. Both conditions must be met.

Step 6: Consider fuel burn. Recalculate for the expected landing weight and CG. As fuel burns off (from a known arm), the CG shifts. The aircraft must remain within the envelope throughout the entire flight, not just at takeoff.

The CG envelope is a graph in the POH that shows the acceptable range of CG positions for each aircraft weight. The horizontal axis shows CG location (in inches aft of datum), and the vertical axis shows aircraft weight. Your calculated weight and CG must plot within the enclosed area.

The envelope is not rectangular — it typically narrows at higher weights, meaning the acceptable CG range becomes smaller as the aircraft gets heavier. This reflects the reduced margin for stability and control at higher weights. Some aircraft have separate envelopes for normal and utility category operations, with the utility envelope being more restrictive.

Common GA examples illustrate the typical ranges: a Cessna 172S has a forward CG limit around 35.0 inches aft of datum and an aft limit around 47.3 inches, with a maximum ramp weight of 2,558 lbs. A Piper PA-28-181 Archer has a CG range of roughly 82.0 to 93.0 inches aft of datum with a max gross weight of 2,550 lbs. Always use the specific numbers from your aircraft's POH — different serial numbers may have different empty weights and CG positions.

The CG position directly affects how an aircraft handles. Pilots must understand these effects to appreciate why CG limits exist and why exceeding them is dangerous:

Forward CG: Increases longitudinal stability (the aircraft resists pitch changes more strongly). However, it also increases stall speed because the tail must produce more downforce, increases fuel consumption due to higher induced drag from the tail downforce, and requires more elevator back-pressure during landing flare. At the forward limit, the aircraft may not have sufficient elevator authority to flare at low speeds — this is why the forward limit exists.

Aft CG:Decreases longitudinal stability, making the aircraft more responsive to pitch inputs — which initially feels "lighter" and more agile. It reduces stall speed and fuel consumption. However, as CG moves further aft, stability decreases to the point where the aircraft may become uncontrollable in pitch. Stall recovery may become impossible because the aircraft lacks the nose-down pitching moment needed to break the stall. A spin entered with an aft CG beyond limits may be unrecoverable.

Lateral CG: While less commonly calculated, lateral CG (side-to-side balance) matters in aircraft with asymmetric loading. Significant lateral CG offset requires constant aileron input, increases pilot workload, and reduces performance. Most POHs do not require formal lateral CG calculations but advise balanced loading.

Fuel is the one variable that changes during flight, and its effect on W&B must be considered for the entire flight profile. Aviation gasoline (100LL) weighs 6.0 pounds per gallon. Jet-A weighs approximately 6.7 pounds per gallon, though this varies with temperature.

When planning, calculate W&B for at least two conditions: takeoff (maximum weight) and landing (after expected fuel burn). If the fuel tanks are located ahead of the CG, burning fuel shifts the CG aft. If behind the CG, burning fuel shifts it forward. Understanding this shift is critical — an aircraft that departs within the envelope may drift outside it during flight if fuel burn moves the CG beyond limits.

A common real-world scenario: a four-seat aircraft with two heavy rear-seat passengers and full fuel is within limits at takeoff. After burning 30 gallons (180 lbs) from wing tanks located near the CG, the weight decreases but the heavy rear passengers remain, shifting the CG aft. The pilot must verify the landing CG is still within the envelope.

Never reduce fuel load to solve a weight problem without rechecking range and reserve requirements. The minimum fuel reserves under VFR (14 CFR 91.151) are 30 minutes at cruise speed during day and 45 minutes at night. IFR reserves (14 CFR 91.167) require fuel to the first airport of intended landing, then to the alternate, then 45 minutes at normal cruise.