Maintenance Records 4: Aircraft Weight and Balance MR4

Weight & Balance

• Aircraft lift is typically concentrated approximately one third of the way back from the wing's leading edge.
• An aircraft's centre of gravity is the point at which all the aircraft weight can be considered concentrated.
• The center of gravity is located slightly ahead of the center of lift.
• The C of G forward of the C of L results in a force that tries to pitch the nose of the aircraft down.
• Nose down force is balanced by a tail load (lift/drag) that pulls the nose up and the aircraft levels.
• The amount of load is determined by airspeed.
• As airspeed drops off, the weight ahead of the centre of lift pulls the nose down, and the airplane automatically regains the speed it lost

3 Elements to Weight & Balance control

• The weighing of the aircraft and its design limits
• Maintenance of accurate weight and balance records.
• Proper loading of the aircraft.
• It is important to distinguish between an aircraft weighing for the technical record (maintenance) and the weight of an aircraft when loaded and prepared for dispatch (flight crew).

Weight & Balance Loading Problems

• Aircraft loading must be done properly any of the following conditions adversely affect the aircraft's flight characteristics and performance:
• Maximum overloaded
• Too much weight forward
• Too much weight aft

Weight Limitations

• If the aircraft is overloaded, there can be effects on its performance that have to be considered.
• Loading an aircraft such that the centre of gravity is forward of the forward limit, can have a number of challenging and potentially dangerous results
• Loading an aircraft such that the C of G is too far aft, can have challenging and dangerous results
• Aircraft is approved and type certified with its weight limitations, or maximums, and the allowable centre of gravity range specified, called the CG envelope.
• Conformity with the approved type design (certification basis) must be established, including these weight and C of G specifications

Regulations

• CAR Part V Subpart 21 relates to the requirements for type certificates.
• The location of the centre of gravity affects the stability of an aircraft.
• When an aircraft is outside of its weight and C of G range/limits, there can be potential loss of lift, loss of control and loss of the aircraft and its occupants
• The allowable C of G range is the furthest forward CG location to the furthest aft CG location specified by the manufacturer
• The centre of gravity of an aircraft, or C of G, or CG, is a point along the longitudinal axis of an aircraft at which all of the weight may be considered to be concentrated.
• It is the point at which the aircraft would balance if it were possible to suspend it from that point.
• A pilot must comply with the aircraft's airworthiness certificate and regulations by calculating weight and balance accurately for every flight and ensuring that they are within the aircraft's permissible limits

Weight Terminology

• Empty Weight/Basic Empty Weight is the weight of the standard aircraft, any optional equipment, fixed ballast, unusable fuel, full operating fluids including oil, hydraulics and any fluid required for normal operation of aircraft systems. It excludes potable water, lavatory pre-charge and water intended for injection in the engine.
• The CAR Part 101.01 defines the parts or contents that are part of, or carried on board, the aircraft that are part of the aircrafts empty weight.
• Licensed Empty Weight is similar to basic empty weight and terminology used in reference to aircraft certified prior to March 1, 1978
• Licensed empty weight differs from basic empty weight only in that licensed empty weight does not include full engine oil.
• Standard Empty Weight is the basic empty weight minus optional equipment, and is obtained from the aircraft manufacturer
• Tare Weight is the weight of the chocks, blocks and jacks, ie. everything that is not part of the aircraft
• Net Weight is scale weight minus tare weight.
• Operational Empty Weight (Zero Fuel Weight) is the actual weight of the aircraft before loading for dispatch, which can include removable equipment, including safety equipment, flight crewmembers and associated baggage, unusable fuel and is defined by the air operator

Weight Tables

• Transport Canada Aeronautical Information Manual (TC AIM) - TP 14371 includes standards weight tables.
• The operational empty weight is the actual weight of the aircraft before loading for dispatch and may include: removable equipment, flight crewmembers and crew members (including baggage), oil, unusable fuel, as well as emergency equipment and should be defined by the air operator. It does not include usable fuel and payload
• The standard weights include:
  • Avgas: 6 lbs/gal
  • Turbine Fuel: 6.7 lbs/gal
  • Oil: 7.5 lbs/gal Water: 8.35 lbs/gal
  • Crew and passengers: 170 lbs/person (for utility aircraft, 190 lbs/person)

Types of Load

• Payload is the sum of the weight of the flight crew, passengers, cargo and baggage.
• Useful Load is the sum of: -Payload
  • Usable fuel
  • Full operating fluids

Weight Limitations

• Maximum Ramp Weight is the maximum weight approved for ground operations.
• Maximum Certificated Take-Off Weight is the maximum take-off weight identified in the type certificate.
• Maximum Permissable Take-Off Weight is the maximum take-off weight approved by the regulatory authority
• Maximum Landing Weight is the maximum allowable weight at which an aircraft can be landed

Additional Regulations

• Pilots must recognize the effect of weight and balance on the performance and handling of aircraft, particularly in combination with performance-reducing factors, such as contaminated runways, aircraft icing, degraded engine performance, severe or uncoordinated manoeuvres, turbulence, high ambient temperatures and emergency situations
• A pilot must recognize the effect of weight and balance on the performance and handling of aircraft.
• In accordance with AIM 3.4.2, it is mandatory to calculate weight and balance accurately for every flight and ensure that they are within the aircraft's permissible limits in order to comply with the aircraft airworthiness certificate and conform to the regulations.
• Every aircraft owner shall keep technical records in respect of the aircraft including, a journey log and a separate technical record for the airframe, each installed engine and each variable-pitch propeller.
• Except where otherwise provided under the terms of a fleet empty weight and balance program referred to in subsection 706.06(3), an empty weight and balance report that meets the applicable standards set out in Standard 571 — Maintenance.
• The technical records required by paragraph (1)(b) may consist of separate technical records for each component installed in the airframe, engine or propeller.
• For a weight and balance report, the empty weight of an aircraft stated in a weight and balance report shall include all items required by the basis of the aircraft type certification, and all additional items of installed equipment. Any item not forming part of the type design shall be entered in an equipment list with its associated weight and moment, and constitutes a part of the weight and balance report.

Aircraft Axes

• Aircraft have 3 axes
• The longitudinal axis
• The vertical axis
• The lateral axis
• The three axes intersect at the airplane's centre of gravity.

Fuselage Stations

• A fuselage station is a distance in inches, measured perpendicular to the longitudinal axis of the aircraft with respect to the datum.
• The datum is an imaginary vertical plane from which all horizontal measurements are taken with the aircraft in a level flight attitude
• There is no fixed rule for the location of the datum.
• It can be located on the nose, the firewall, the leading or trailing edge of the wing, or at an imaginary point in space ahead of the aircraft.
• The waterline is a horizontal reference plane from which vertical measurements in an aircraft may be taken.
• A butt line or buttock line is a distance to the right or left of the fuselage centerline, referenced to the longitudinal centerline.

Wing Stations

• Wing stations are measured from the centerline of the fuselage or buttock line zero.
• Wing stations are used to indicate locations laterally along the wings of the aircraft.
• Wing station 00.00 is located in the center of the fuselage at the butt line, dividing the airplane into two symmetrical halves LEFT and RIGHT.
• On one particular aircraft, the butt line numbers are used from station 00.00 to station 99.60, and outboard of station 99.60 the measurements are referred to as wing stations
• On most aircraft:
  • Wing station numbers are used in wing areas
  • Butt line numbers indicate fuselage stations left and right of station 00.00.
• On all aircraft both Wing Station and Butt Line measurements have the same reference point, BL 00.00.