Guide for Student Pilots to Understand and Calculate Weight and Balance

In the intricate world of aviation, understanding weight and balance concepts is paramount to ensuring safe flights. Weight and balance calculations are essential to maintain optimal performance and prevent catastrophic failures. This guide delves into the key concepts, methodologies, and safety practices related to the weight of the aircraft, helping pilots and aviation professionals master these critical skills.

The Importance of Weight and Balance in Aviation

Ensuring Safe Flight Operations

The weight and balance of an airplane are crucial factors in ensuring safe flight operations. Proper weight and balance calculations prevent a multitude of in-flight issues, such as stalls and loss of control. If an aircraft’s weight exceeds the maximum maximum weight allowed or if the center of gravity (CG) is not within acceptable limits, it can lead to disastrous consequences. Pilots must understand the aircraft’s weight and balance data to ensure that every flight adheres to these limits.

Moreover, the aircraft flight manual often outlines the appropriate weight and center of gravity parameters that must be maintained. Pilots must calculate the weight accurately, including the fuel weight and baggage, to ensure the total weight does not exceed the allowable maximum weight. Ensuring that the aircraft’s weight falls within the weight limits is not just a regulatory requirement, but a fundamental aspect of flight safety.

Impact on Aircraft Performance

How you load your aircraft matters, because An incorrect balance can significantly affect the performance of an aircraft. If the weight of the airplane is not properly managed, it can alter the angle of attack, or increase trim drag, leading to inefficient flight dynamics and increased fuel consumption. Moreover, improper loading can cause the airplane to become unstable, making it difficult to control. Weight and balance calculations help in determining the proper distribution of the aircraft's weight, ensuring it can achieve optimal performance.

The aircraft’s basic empty weight includes the structure of the aircraft and unusable fuel. Knowing these details allows pilots to understand how much weight they can add, including passengers and cargo. This ensures that the airplane’s weight and balance are within prescribed operational limits, thus maintaining the aircraft’s performance and structural integrity.

Understanding Key Weight and Balance Terms

Basic Empty Weight and Standard Empty Weight

The basic empty weight of the aircraft includes the weight of the airplane, unusable fuel, and other essential fluids. This term is pivotal for calculating the aircraft's weight and balance since it forms the baseline from which all other weights are added. The standard empty weight is similar but might exclude some optional equipment. Understanding these terms helps pilots accurately determine the balance and ensure they do not exceed the gross weight limits.

Standard empty weight often serves as a reference for manufacturers when constructing performance graphs and operational handbooks. Pilots need to know both the basic empty weight and the standard empty weight to calculate the total weight, including any additional equipment or modifications. Accurate knowledge of these weights is essential for making precise weight and balance calculations.

Ramp Weight and Maximum Ramp Weight

Ramp weight refers to the total weight of an aircraft while it is on the ramp before engine start. It includes the basic empty weight, fuel, passengers, and cargo. Maximum ramp weight is the limit to which the aircraft can be loaded while on the ground. It is slightly higher than the maximum takeoff weight, accounting for the fuel burn that happens before takeoff. Understanding ramp weight and maximum ramp weight is crucial for pilots to ensure they operate within safe limits.

Pilots use the ramp weight to ensure all calculations for the flight are accurate, considering any fuel and oil added during preflight. If the ramp weight exceeds the maximum ramp weight, the aircraft would not comply with safety standards. Therefore, knowing these details helps in planning how much weight to add or reduce to stay within acceptable safety margins.

Takeoff Weight and Maximum Takeoff Weight

Takeoff weight is the total weight of the aircraft at the moment of takeoff, including fuel, passengers, and baggage. The maximum takeoff weight is the maximum weight at which the aircraft is certified to lift off the ground. Adhering to this limit is essential as exceeding it can impair the aircraft's ability to climb, maneuver, and maintain a safe flight path. Proper weight and balance calculations ensure takeoff weight remains within the approved limits.

Pilots need to consider fuel burn, which affects the takeoff weight. Calculations must account for the difference between the ramp weight and the takeoff weight to prevent overloading the aircraft. This comprehension ensures the aircraft can achieve necessary performance criteria during the critical takeoff phase.

Landing Weight and Maximum Landing Weight

Landing weight is the total weight of the aircraft when it lands, and maximum landing weight is the highest weight at which the aircraft can land safely. Overloading beyond this limit can cause structural damage or an increased risk of accidents during landing. Accurate assessments of landing weight, factoring in fuel consumption and other variables, are crucial for flight safety. Ensuring that the landing weight is within the maximum permissible limits safeguards the aircraft structure and ensures safe landings under all conditions.

Pilots utilize weight and balance charts to confirm the landing weight is within acceptable parameters. Calculations should include any potential in-flight adjustments to fuel and cargo. Regularly monitoring these variables helps pilots maintain control and assures successful compliance with safety standards upon landing.

Center of Gravity (CG)

The center of gravity (CG) is the point where the aircraft's weight is perfectly balanced. Properly positioning the CG is essential for the stability and control of the airplane. If the CG is too far forward or aft, it can lead to poor handling characteristics and increased risk of accidents. Pilots must calculate the CG accurately to ensure that the weight distribution within the aircraft is suitable for safe operation. A well-balanced CG enhances the aircraft's maneuverability and prevents undue stress on the airframe.

Pilots must refer to the aircraft-specific balance handbook to determine the permissible CG range. They need to carefully adjust baggage, passengers, and fuel to keep the CG within these limits. An incorrect CG can make the aircraft unstable, especially during critical phases like takeoff and landing. Thus, understanding and managing the CG is a fundamental part of pre-flight preparation.

Calculating Aircraft Weight and Balance

Gathering Necessary Data

Before calculating the aircraft's weight and balance, pilots must gather all relevant data. This includes the airplane’s basic empty weight, weight of passengers, baggage, and fuel weight. Accurate data collection ensures the calculations are precise and within the aircraft's operational limits. By adhering to the weight and balance handbook provided by the manufacturer, pilots can gather the necessary data systematically to perform their calculations.

Additional factors such as the weight of any additional equipment or modifications must also be considered. All collected data must be verified against the weight and balance charts to ensure they align with the aircraft's max gross weight. Proper data collection is the first step towards making accurate weight and balance calculations, ensuring safe and efficient flight operations.

Using Weight and Balance Charts

Weight and balance charts are vital tools in calculating the aircraft's total weight and CG. These charts provide a graphical representation of the weight and moment values, helping pilots visualize whether the aircraft's loading falls within acceptable limits. Pilots must become proficient in reading and interpreting these charts to ensure their calculations are accurate. Using these charts helps pilots ensure that the airplane’s weight and balance comply with all regulatory requirements.

Weight and balance charts typically include parameters for estimating fuel burn, passenger distribution, and baggage loading. By plotting the collected data on these charts, pilots can determine the CG and ensure it is properly situated. Proficiency in using these charts is essential for maintaining the aircraft’s performance and safety throughout the flight.

How to Calculate Aircraft Weight and Balance Step-by-Step

Step-by-Step Calculation Process

Calculating the weight and balance involves a step-by-step process beginning with compiling all pertinent data, including licensed empty weight and weight of the airplane after loading passengers, cargo, and fuel. Next, pilots must calculate the moment for each weight entry by multiplying the weight and moment arm. Adding these moments and dividing by the total weight yields the CG, which must fall within prescribed limits. Pilots must repeat this process to ensure any changes, like fuel burn, are accounted for accurately throughout the flight.

To ensure consistent accuracy, pilots should use weight and balance calculators available for specific aircraft. These tools provide reliable and efficient means to verify hand-calculated results. The thorough and methodical application of these steps guarantees safe flight operations adhering to all regulatory and safety standards.

Finding the Weight and Balance Using the Calculation Method

Step 1 – Create Your Weight and Balance Table

Start with a blank table to fill out for every flight. While many flight schools and FBOs provide a planning sheet, you can easily create your own.

The table should have always have the four columns: "Item", “Weight,” “Arm,” and “Moment.” Often pilots or flight schools include fuel in gallons and use that to calculate the weight.  Here is a version of typical flight training weight and balance worksheet: 

At the top, write the formula for calculating weight and balance to remind yourself:

Weight x Arm = Moment

The common line items in your table will vary based on the loading stations available in your aircraft, but it typically begins with the empty weight of the airplane. The white cells will always be the same for the same aircraft, so when creating a sheet for a commonly used aircraft, you'll likely have them pre filled. The yellow cells will be values that you will need to enter or calculate for each flight. the blue and green cells indicate your calculated CG at takeoff and landing. You'll have 2 sections one for takeoff weight and cg and one for landing weight and cg.

Step 2 – Determine the Aircraft’s Empty Weight and Moment

Identify the specific aircraft you'll be flying to retrieve its empty weight and moment data from the official record in the POH/AFM. Only use the official records, as these figures come from the last time the aircraft was physically weighed by a mechanic and are signed by an A&P.

Input the empty weight and total moments into the first row of your table.

Step 3 – Determine the Arm for Each Station

Refer to  your POH/AFM to find the arm for each weight on your list. Fill out your table with these values.

If you fly this plane regularly, you might save the sheet like this as a template for future flights. Be sure to update the model and tail number in the header to avoid using the wrong template.

Step 4 – Weigh Your Passengers and Gear

Accurate weights are critical, especially in smaller aircraft. Use exact numbers for all items, including passengers. Ask your passengers for their weight or use a scale provided by many FBOs. Don’t forget to account for extra items like heavy clothing.

To determine fuel weight, multiply the number of gallons by the weight of the fuel type (e.g., Avgas is 6.02 pounds per gallon, Jet-A varies but is approximately 7 pounds per gallon).

NOTE: Fuel used in taxi and cruise are shown as a negatives to remind you to subtract the weights in your weight calculation.

Include all items not permanently fixed in the airplane, such as flight bags and spare parts.

Step 5 – Calculate the Moment for Each Item

Multiply the weight by the arm for each row to determine the moment.

Step 6 – Calculate the Total Weights

Sum the weights in the weight column for takeoff (subtracting fuel used in taxi). Ensure the total weight is below the maximum takeoff weight for your aircraft.

If the total exceeds the maximum takeoff weight, verify your calculations. You may need to offload some items or reduce fuel if it is safe to do so.

Step 7 – Determine Total Moment and CG

Your POH/AFM will show how to verify if the aircraft is in balance, using total moments, total arm (CG), or both.

Add up the moments. This may be sufficient if your POH/AFM includes a chart for loaded moments. Ensure to adjust for the appropriate index, typically dividing by 100 or 1,000.

To calculate the CG, divide the total moment by the total weight. Avoid adding all the arms directly; instead, use the moments and weights to determine the CG.

* Takeoff CG = Takeoff Condition Moment / Takeoff Condition Weight = 95416 / 2329 = 41.0

* Landing CG = Takeoff Condition Moment / Takeoff Condition Weight = 86747 / 2149 = 40.4

Step 8 – Plot Your CG to insure you are in the CG Envelope

Plotting your take off and landing CG on your aircraft center of gravity limits chart is a helpful way to see where in the CG envelope you are operating. Here is the plot for the sample flight calculated above. You'll need to use the CG limits for your aircraft.

You can download a excel template of the above worksheet complete with the calculations already done to create your own weight and balance calculator for your specific aircraft.

Factors Affecting Aircraft Weight and Balance

Fuel and Oil

Fuel and oil significantly impact an aircraft's weight and balance. As fuel burns during a flight, the weight of the aircraft changes, affecting the CG. Pilots must include fuel weight in their initial calculations and account for its reduction during flight. Proper management ensures the aircraft remains balanced and within safe operational limits. Gauging the impact of fuel and oil is essential for precise weight and balance calculations.

Pilots should regularly check fuel levels and predict fuel consumption patterns to adjust their calculations accordingly. Comprehensive understanding of how fuel and oil weights influence the aircraft’s center of gravity helps pilots make necessary in-flight adjustments to maintain optimal flight conditions and safety protocols.

Passengers and Cargo

The weight and distribution of passengers and cargo significantly affect the aircraft's center of gravity. Incorrect placement can result in an aft or forward CG, leading to instability or handling issues. Pilots must carefully plan the loading of passengers and cargo, using weight and balance data to ensure the total weight remains within safe limits and the CG is appropriately positioned. Proper loading practices prevent overloading and balance issues, ensuring the aircraft's stability and control.

Considering passengers’ and cargo’s impact on flight dynamics, pilots must systematically distribute weights in accordance with the aircraft's specific loading instructions. Using detailed load sheets and charts helps ensure equitable weight distribution, preventing imbalances that might compromise flight safety and performance.

Aircraft Modifications

Modifications to the aircraft, including added equipment or structural changes, alter the basic empty weight and potentially affect the center of gravity. Pilots must take these changes into account and re-evaluate the weight and balance accordingly. Ensuring proper documentation and understanding how modifications impact flight parameters is essential. Regular updates to weight and balance data are necessary to reflect these changes accurately for safe operation.

Aircraft modifications can introduce new variables to the weight and balance equation, necessitating rigorous reassessment using the manufacturer's updated guidelines and documentation. By conducting thorough and precise evaluations of post-modification conditions, pilots can maintain adherence to weight and balance limits, ensuring continued compliance with safety standards.

Tools and Resources for Calculating Weight and Balance

Weight and Balance Calculators

Weight and balance calculators are essential tools that assist pilots in precisely calculating the aircraft's total weight and CG. These calculators simplify the process by allowing input of various weights and automatically calculating the resulting balance. Using these tools ensures that calculations are accurate and efficient, reducing the likelihood of human error. Pilots rely on these devices to validate their manual computations and ensure flight safety.

Many practical weight and balance calculators are available, offering functionalities that cater to different aircraft requirements. Pilots must familiarize themselves with these calculators to harness their full potential, streamlining the weight and balance check processes and improving operational efficiency.

Mobile Apps and Software

Modern technology offers a plethora of mobile apps and software designed to aid in weight and balance calculations. These applications provide convenient and user-friendly interfaces, allowing pilots to perform calculations on-the-go. Mobile apps often include features for storing aircraft-specific data, making it easier to manage and retrieve information. By using these digital solutions, pilots can enhance accuracy and efficiency in determining the aircraft's weight and CG.

Mobile apps and software also offer up-to-date regulatory compliance and can sync with avionics systems for real-time updates. Utilizing these technological advancements ensures that pilots have access to vital information anywhere, anytime, promoting enhanced flight safety and operational readiness.

Aircraft-Specific Manuals

Aircraft-specific manuals, such as the pilot operating handbook, provide detailed information on the aircraft’s weight and balance limits. These manuals include charts, graphs, and tables that are indispensable for accurate calculations. Pilots must thoroughly understand and reference these documents to ensure compliance with manufacturer guidelines and regulatory requirements. These manuals are essential tools for maintaining the aircraft’s performance and ensuring safety during all phases of flight.

Regularly consulting aircraft-specific manuals helps pilots stay abreast of any changes in weight and balance parameters, incorporating these into their pre-flight planning. Consistent use of these resources forms the backbone of accurate weight and balance management, reinforcing adherence to stipulated safety standards and operational practices.

Common Weight and Balance Mistakes and How to Avoid Them

Overloading the Aircraft

One of the most critical mistakes in aviation is overloading the aircraft. Exceeding the gross weight limits can compromise the aircraft's structural integrity and impair its performance. Pilots must be vigilant in ensuring that the total weight, including passengers, baggage, and fuel, does not exceed the maximum allowable limits. Accurate weight and balance calculations and adherence to guidelines are essential for avoiding overloading issues.

Pilots should conduct meticulous pre-flight checks and use checklists to verify all weight elements. Ensuring that the total payload falls within permissible ranges is a fundamental responsibility, critical for maintaining optimal safety and airworthiness during flight operations.

Incorrect CG Calculations

Miscalculating the center of gravity can lead to severe in-flight stability issues. An incorrect CG can cause adverse handling characteristics and potentially hazardous flight conditions. Pilots must accurately calculate the CG and ensure it falls within the acceptable range specified in the aircraft’s balance handbook. Utilizing weight and balance charts and calculators can help reduce errors and verify the placement of the aircraft's CG.

By rigorously cross-checking CG calculations against standardized charts and applying methodical processes, pilots can avoid critical miscalculations. Emphasizing precision and adherence to established protocols ensures balanced and stable flight operations, mitigating risks associated with improper CG placement.

Failing to Account for Fuel Burn

Failing to account for fuel burn during a flight can result in weight and balance discrepancies. As fuel is consumed, the aircraft's CG shifts, potentially leading to imbalance and instability. Pilots must include fuel burn in their weight and balance calculations to ensure the CG remains within safe limits throughout the flight. Continuous monitoring and adjustments during flight are necessary to maintain proper balance.

Understanding fuel consumption patterns and their impact on the aircraft’s weight and balance is crucial for effective flight management. Through proactive adjustment and continuous assessment, pilots can ensure that fuel depletion does not lead to safety compromises or regulatory infringements.

Real-World Examples of Weight and Balance Issues

Case Studies of Weight and Balance Accidents

Numerous case studies highlight the importance of proper weight and balance calculations. Accidents caused by overloaded aircraft or incorrect CG positioning serve as stark reminders of the necessity of adhering to weight and balance guidelines. Studying these cases provides valuable insights into the consequences of mismanagement and emphasizes the importance of meticulous planning and execution. Pilots can learn from these incidents to improve their understanding and application of weight and balance principles.

Case studies often detail specific instances where weight and balance miscalculations led to catastrophic outcomes. Examining these details equips aviation professionals with the knowledge required to avoid similar pitfalls, reinforcing the significance of meticulous adherence to established safety protocols and guidelines.

Pilot's failure to Check Weight Kills Instagram Star!

On April 9, 2018, a tragic accident involving a Piper PA-24-260 in Scottsdale, Arizona, resulted in the fiery deaths of all onboard, including several social media influencers. The plane, tail number N9456P, crashed shortly after takeoff due to critical issues, primarily related to improper weight and balance. This incident serves as a stark reminder of the paramount importance of adhering to weight and balance principles in aviation, which, when neglected, can lead to catastrophic outcomes.

The video embedded below provides a detailed debrief of the events leading to the crash, highlighting the mistakes and oversights that contributed to the tragedy. It underscores crucial lessons for pilots, emphasizing the need for thorough pre-flight checks, accurate weight and balance calculations, and strict adherence to safety regulations. As you watch, reflect on the importance of these measures to prevent such disasters and honor the memory of those who lost their lives.

You can review the full NTSB Docket of the Aviation Investigation - WPR18FA119  or download the NTSB Final Report.

Lessons Learned from Past Incidents

Past incidents involving weight and balance errors offer crucial lessons for the aviation community. These incidents often resulted from a lack of proper weight management or failure to adhere to CG limits. By analyzing these events, pilots can identify common mistakes and implement strategies to avoid them. Learning from past incidents promotes a culture of safety and continuous improvement in aviation practices.

Incorporating lessons learned into training programs and operational protocols ensures that future flight crews are better prepared. Emphasizing these educational aspects fosters an environment geared towards sustainable safety enhancements and operational excellence, contributing to the overall reliability of aviation practices.

Weight and Balance Considerations for Every Flight

Pre-Flight Planning and Checks

Pre-flight planning is essential for ensuring accurate weight and balance calculations. Pilots must perform comprehensive checks of all weight-related elements, including passengers, baggage, fuel, and equipment. Ensuring that all data aligns with the weight and balance handbook guidelines is crucial for safe flight operations. Meticulous pre-flight planning helps prevent overloading and improper CG positioning, ensuring the aircraft is ready for a safe and efficient flight.

Conducting thorough pre-flight inspections and double-checking all weight-related components guarantees comprehensive preparation. Integrating these practices into standard operating procedures enhances overall flight readiness and safety, aligning with regulatory standards and best practice recommendations.

In-Flight Adjustments

In-flight adjustments are sometimes necessary to maintain proper weight and balance. Changes in fuel levels, passenger movements, and cargo shifts can impact the aircraft's CG. Pilots must be prepared to make real-time adjustments to ensure the aircraft remains balanced and stable. Continuous monitoring and quick decision-making are essential skills for managing these dynamic changes during flight.

Incorporating regular assessments and anticipatory measures into flight operations ensures pilots can adapt to in-flight changes effectively. By maintaining vigilance and applying swift corrective actions, pilots can uphold weight and balance accuracy, thereby safeguarding flight integrity and passenger safety.

Special Weight and Balance Considerations for Student Pilots

Learning the Basics

For student pilots, mastering weight and balance fundamentals is a crucial part of their training. Understanding basic concepts such as the aircraft's basic empty weight, CG, and weight limits lays the foundation for safe flying practices. Instructors must emphasize the importance of accurate calculations and adherence to guidelines. Comprehensive training in these basics equips student pilots with the skills necessary to ensure proper weight management and flight safety.

Structured educational programs and hands-on practice in weight and balance assessments are integral to developing proficient student pilots. Implementing foundational knowledge and real-world applications ensures that future aviators achieve a high standard of operational competency and safety awareness.

Common Challenges and Solutions

Student pilots often face challenges in understanding and applying weight and balance principles. Common issues include miscalculations and difficulty in interpreting weight and balance charts. Providing practical examples and guided practice can help overcome these challenges. Instructors should offer continuous support and reinforce the importance of precise calculations to build confidence in their students. Utilizing simulation tools and real-world scenarios during training can also enhance understanding and application of these critical concepts.

By addressing these challenges head-on and providing clear, consistent guidance, instructors can help student pilots develop strong skills in weight and balance management. Encouraging questions and fostering a learning environment where mistakes are used as teaching moments further solidifies students' understanding. These practices ensure that new pilots are well-prepared to manage aircraft weight and balance effectively, contributing to overall aviation safety.

Further Reading for Student Pilots on Weight and Balance

• FAA aircraft weight and balance handbook
• Pilot's Handbook of Aeronautical Knowledge Chapter 10 weight and balance
• Wikipedia: Center of gravity of an aircraft 

Q: What is aircraft weight and balance?

A: Aircraft weight and balance refer to the process of ensuring that the aircraft's total weight and its distribution are within the safety margins outlined by the manufacturer and federal aviation authorities. Proper balance ensures stable flight characteristics and prevents control issues.

Q: Why is the weight and balance of an aircraft important?

A: Maintaining the correct weight and balance is critical for safe flight operations. An improperly balanced or overweight aircraft can lead to poor handling, reduced performance, increased fuel consumption, and even flight instability. Ensuring proper weight and balance is essential for the aircraft's structural integrity and overall safety.

Q: How is the balance of an aircraft calculated?

A: The balance of an aircraft is typically calculated using the aircraft weight and balance formula, which involves determining the center of gravity (CG) by using the weight times the arm (distance) of each component. The total moment is divided by the total weight to find the CG. The CG must fall within a specific range known as the CG envelope to ensure safe flight.

Q: What is the CG envelope?

A: The CG envelope is the range within which the center of gravity must be located for safe flight. This range is defined by the manufacturer and is detailed in the aircraft’s operating manual. It ensures both lateral and longitudinal balance of the aircraft, contributing to stable flight characteristics and control.

Q: What is the maximum allowable weight for an aircraft?

A: The maximum allowable weight, also known as the maximum gross weight, is the highest weight at which the aircraft is certified to operate safely. This includes the weight of the airframe, passengers, cargo, fuel, and other load items. Exceeding this weight can adversely affect performance and safety.

Q: How can I determine if my aircraft is within weight and balance limitations?

A: You can determine if your aircraft is within weight and balance limitations by consulting the weight and balance information provided in the aircraft’s operating manual and performing a weight and balance check before each flight. This involves calculating the total weight and ensuring the CG is within the specified envelope.

Q: What is the standard weight used for calculating the weight of an airplane?

A: The standard weight refers to predetermined average weights for passengers, baggage, and fuel used in calculating the aircraft’s total weight. These weights are based on regulatory guidelines and statistical averages to ensure the aircraft remains within safety limits during operations.

Q: How does the weight shift formula work in weight and balance calculations?

A: The weight shift formula helps determine the effect of shifting weight within the aircraft. It involves calculating how moving a certain weight to a different location will impact the aircraft's center of gravity and balance. This calculation ensures that any adjustments maintain the CG within the safe range.

Q: What precautions should be taken when loading a training aircraft?

A: When loading a training aircraft, it's important to ensure that the weight and balance are within prescribed limits, avoiding overloading and properly securing all items. Pilots should also verify that the CG is within the acceptable envelope. Regular checks and adherence to the aircraft’s operating manual are essential for safe operations.

Q: What actions should be taken if an aircraft exceeds its maximum gross weight?

A: If an aircraft exceeds its maximum gross weight, you need to reduce the weight by offloading some cargo, fuel, or passengers until the aircraft is within acceptable weight and balance limitations. Operating an overweight aircraft is unsafe and illegal. Always ensure compliance with weight and balance regulations before flight.

Q: What Terms and Definitions apply to Weight and Balance

The Pilot's Handbook of Aeronautical Knowledge says pilot should be familiar with the appropriate terms regarding weight and balance. The following list of terms and their definitions is standardized, and knowledge of these terms aids the pilot to better understand weight and balance calculations of any aircraft. Terms defined by the General Aviation Manufacturers Association (GAMA) as industry standard are marked in the titles with GAMA.

• Arm (moment arm): The horizontal distance in inches from the reference datum line to the CG of an item. The algebraic sign is plus (+) if measured aft of the datum and minus (–) if measured forward of the datum.

• Basic empty weight (GAMA): The standard empty weight plus the weight of optional and special equipment that have been installed.

• Center of gravity (CG): The point about which an aircraft would balance if it were possible to suspend it at that point. It is the mass center of the aircraft or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. It may be expressed in inches from the reference datum or in percent of MAC. The CG is a three-dimensional point with longitudinal, lateral, and vertical positioning in the aircraft.

• CG limits: The specified forward and aft points within which the CG must be located during flight. These limits are indicated on pertinent aircraft specifications.

• CG range: The distance between the forward and aft CG limits indicated on pertinent aircraft specifications.

• Datum (reference datum): An imaginary vertical plane or line from which all measurements of arm are taken. The datum is established by the manufacturer. Once the datum has been selected, all moment arms and the location of CG range are measured from this point.

• Delta: A Greek letter expressed by the symbol Δ to indicate a change of values. As an example, ΔCG indicates a change (or movement) of the CG.

• Floor load limit: The maximum weight the floor can sustain per square inch/foot as provided by the manufacturer.

• Fuel load: The expendable part of the load of the aircraft. It includes only usable fuel, not fuel required to fill the lines or that which remains trapped in the tank sumps.

• Licensed empty weight: The empty weight that consists of the airframe, engine(s), unusable fuel, and undrainable oil plus standard and optional equipment as specified in the equipment list. Some manufacturers used this term prior to GAMA standardization.

• Maximum landing weight: The greatest weight that an aircraft is normally allowed to have at landing.

• Maximum ramp weight: The total weight of a loaded aircraft including all fuel. It is greater than the takeoff weight due to the fuel that will be burned during the taxi and run-up operations. Ramp weight may also be referred to as taxi weight.

• Maximum takeoff weight: The maximum allowable weight for takeoff.

• Maximum weight: The maximum authorized weight of the aircraft and all of its equipment as specified in the TCDS for the aircraft.

• Maximum zero fuel weight (GAMA): The maximum weight, exclusive of usable fuel.

• Mean aerodynamic chord (MAC): The average distance from the leading edge to the trailing edge of the wing.

• Moment: The product of the weight of an item multiplied by its arm. Moments are expressed in pound-inches (in-lb). Total moment is the weight of the airplane multiplied by the distance between the datum and the CG.

• Moment index (or index): A moment divided by a constant such as 100, 1,000, or 10,000. The purpose of using a moment index is to simplify weight and balance computations of aircraft where heavy items and long arms result in large, unmanageable numbers.

• Payload (GAMA): The weight of occupants, cargo, and baggage.

• Standard empty weight (GAMA): Aircraft weight that consists of the airframe, engines, and all items of operating equipment that have fixed locations and are permanently installed in the aircraft, including fixed ballast, hydraulic fluid, unusable fuel, and full engine oil.

• Standard weights: Established weights for numerous items involved in weight and balance computations. These weights should not be used if actual weights are available. Some of the standard weights are:

  • Gasoline: 6 lb/US gal
  • Jet A, Jet A-1: 6.8 lb/US gal
  • Jet B: 6.5 lb/US gal
  • Oil: 7.5 lb/US gal
  • Water: 8.35 lb/US gal

• Station: A location in the aircraft that is identified by a number designating its distance in inches from the datum. The datum is, therefore, identified as station zero. An item located at station +50 would have an arm of 50 inches.

• Useful load: The weight of the pilot, copilot, passengers, baggage, usable fuel, and drainable oil. It is the basic empty weight subtracted from the maximum allowable gross weight. This term applies to general aviation (GA) aircraft only.

  Source: Pilot's Handbook of Aeronautical Knowledge, page 10-4 and 10-5