Weight and Balance

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Atboh сб, 10/03/2012 - 04:30 |

              Weight and balance

     

  

General
 
The purpose of loadcontrol is granting a safe operation of every flight in respect to the weight and balance of the aircrafts.
We must make sure that any dangerous goods and/or miscellaneous special loads are loaded according to regulations.
By correct loading of baggage, we ensure that passenger baggage is delivered on time after arrival and the transfer of baggage
connecting to other flights is granted. Loadcontrol can be performed manually or on an EDP system.
Every loadcontroller must be able to issue manual documents in case of system failure.
 
Load Control duties
 
• Precalculation
• Loading Instruction
• Loadsheet
• Notification to Captain
• Dispatch of necessary messages after departure of the aircrafts.
 
 
Policy
 
• Safety always has first priority!
• Priority sequence of economy, punctuality and passenger comfort depends on
 the situation.
• Correct application of load control rules has priority over other station work,
 including punctuality.
 

 

Loadcontrol Manuals
 
As you can't know all necessary information by heart, it is very important that you are used to work with the manuals and
make sure that the manuals are updated and easy to consult at your working place.
 
AHM
The AHM (Aircraft Handling Manual). It contains regulations, guidelines and information for ramp handling, loading,
loadplanning and load control, e.g. passenger, crew, ULD weights, dangerous goods, live animals, messages etc.
The information in this manual is valid for any aircraft type and any station worldwide.
 
Weight and Balance Manuals and AHM560 for Aircrafts
Specific aircraft information is published in the W&B Manuals. It exists for every aircraft type. It contains regulations
and information such as maximum weights, cabin configurations, hold versions, loading regulations and restrictions etc,
generally speaking all information which varies for different aircraft types.
 
Additional Manuals
In certain cases, you might also need information published in other manuals:
PHM
The PHM (Passenger and Baggage Handling Manual) is the manual for passenger handling.
In the PHM you can find information on passenger and baggage handling.
IATA AHM
Danger Goods Regulations
Live Animal Regulations
Other…
 
 

 
General rules
 
Airlines establish following weight values obligatory for weight and balance 
calculations purposes:
a) standard weights (mentioned in AHM 560 procedure):
• crew,
• passenger,
• catering.
b) actual weights:
• baggage,
• cargo,
• mail.
All weights applying in weight and balance calculations must be in kilograms (kg). 
 
Standard weights:
 
1. Crew weights
• Cockpit crew: 85 kg 
• Cabin crew: 75 kg
Crew weight includes cabin baggage. 
Additional crew baggage carried in cargo compartments must be treated as
checked baggage.
Standard crew weights are not applied for crew positioning to/from duty not
directly involved in the operation of the flight, who are occupying passenger
seats (DHC – Dead Head Crew)
 
2. Standard passenger weights 
Passenger category:                      Standard       Alternative standard 
Male                                              84 kg                  88 kg 
Female                                           84 kg                  70 kg 
Child (between 2-12 years)
or infant under 2 years
if occupying a separate seat              35 kg                  35 kg 
Infant under 2 years
if sharing a seat with an adult            0 kg                    0 kg  
a) Scheduled alternative standard weights to be used only in case of weight
and/or balance problems if the number of female is more than 23 % percent
of the total number of adult passengers.
In that case, the commander must be in formed by an appropriate remark in
the SI-part of the loadsheet.
b) Standard passenger weight includes:
⇒ cabin baggage, 
⇒ any infant weight below 2 years of age carried by an adult on one
passenger seat.
 

Principles of Balance 

Generally, there are four forces aff ecting an aircraft during the straightforward flight with a constant
speed as shown on the drawing below:
 
T Thrust
D Drag
L Lift
Q Weight

This case occurs when forces affecting an aircraft and moments from these forces are in balance that
means: Thrust equals Drag and Lift equals Weight.

Thrust equals Drag when an aircraft flies at constant speed:

T = D

 

In this situation two vertical forces remains to be taken into consideration: Lift and Weight.
Lift L is hung in the Centre of Lift and depends on value of a constant speed of an aircraft.
Weight Q is placed in the Centre of Gravity COG and depends on the loading of an aircraft.
The centre of gravity of a body is defined as the point at which its total weight may be considered
to act as a concentrated force.
These two points: Centre of Lift and Ce ntre of Gravity do not usually cover.
In this case a pair of forces is created and aircraft can tend nose down and up because of a moment which
occurs.

Moment equals force multiplied by arm, on which this force affects.

Moment = Force x Arm

To balance an aircraft, that means to eliminate the influence from above moment, additional force
coming from horizontal stabilizer Fн is created. 

 
The sum of three forces: Lift L, Weight Q and Horizontal Stab. Fн must equal zero and the sum of 
moments coming from these forces around a given point must equal zero, then the balance is maintained.

L + Q + Fн = 0              M(L) + M(Q) + M(Fн) = 0 

A force coming from horizontal stabilizer Fн depends on an angle of swing of stabilizer. 
This angle has limited range. That’s why moment coming from a pair of forces Lift L and Weight Q
must not exceed strictly defined value, limited by a moment obtained from a force coming from
horizontal stabilizer M(Fн).

 
Location of Centre of Lift depends on aerodynamics, so we cannot affect on it.
Location of Centre of Gravity can be controlled by appropriate loading of an aircraft.
For each aircraft type therefore the manufacturer specifies a safe range of COG location and operator of
an aircraft must not exceed given limitations.
 
The COG location is defined in following units:
1. %MAC (Mean Aerodynamic Chord) – percent of Mean Aerodynamic Chord.
2. Index - unit without a term
 
1. % MAC – PERCENT OF MEAN AERODYNAMIC CHORD. 
DEFINITION :
The Aerodynamic Chord is the line linking a wing nose and a trailing edge.
 
The Mean Aerodynamic Chord MAC is a conventional chord of a substitute wing with a irregular
rectangle shape having the same aerody namic characteristic as a real wing.
This reference line is used in the design of a wing and its position relative to the wing and the
fuselage is accurately known.
 

LEMAC - Horizontal distance in inches or mete rs from the station zero to location
of the Leading Edge of MAC.

The Safe Range of COG for an aircraft type, for characteristic aircraft weights, 
is specified by the manufacturer and is ex pressed in terms of percentage of MAC.

 
2. INDEX – unit without a term. 

Index expresses an influence of the component weight forces on change of COG position depending on
location of the forces relatively to Ref. Station.
Index – it is an equivalent of moment coming from the component weight forces relatively to their
positions to Ref. Station.

 
Ref. Station – Reference station /axis. Sel ected station around which all indexes values are calculated.

Depending on position of an loaded item on an aircraft re latively to Ref. Station, the value of arms are
following:
• the arms measured forward of Ref. Station are negative ( - )
• the arms measured aft of Ref. Station are positive ( + )

Therefore, each weight of an item loaded on an ai rcraft - relatively to its location - corresponds to
negative or positive index correction, which is a measure of an influence of the load on Centre of Gravity
location.

The conversion from index value to per cent of MAC is obtained from a graph.
The graph represents MAC grids in function of ai rcraft characteristic weight and index values.

 
Terminology
 
Maximum landing weight (MLAW / MLDW)
• This is the maximum permitted weight at which the aircraft may land.
⇒ design – determined by the manufacturer of an aircraft (does not depend
on operational conditions),
⇒ operational – reduced by the operator subject to conditions prevailing at
the airfield of departure or arrival.
• Design MLAW, similarly to design MTOW, may be reduced by the
operator subject because of operational conditions mentioned above.
• Only real MTOW and MLAW values, taking into consideration all
operational factors, are allowed to be used for weight and balance
calculations.
 
Maximum take-off weight (MTOW)
• This is the maximum permitted weight at commencement of the take-off run:
⇒ design – determined by the manufact urer of an aircraft (does not depend on operational conditions), 
⇒ operational – reduced by the operato r subject to conditions prevailing
at the airfield of de parture or arrival .
• Actual MTOW is calculated accordingly to operational conditions of the
runway on the base of Airplane Flight Manual.
• Design MTOW may be reduced by:
a) runway characteristic:
⇒ length,
⇒ slope,
⇒ pavement,
⇒ elevation,
⇒ obstacles on the climb path.
b) weather conditions:
⇒ temperature,
⇒ precipitation,
⇒ wind component.
c) noise abatement rules.  
 
Maximum zero fuel weight (MZFW)
• This is maximum design weight of loaded aircraft without fuel.
• This weight results from the designed strength of the wings.
• The force Lift L -from the wings- acting upwards, together with the force 
Weight Q of the loaded fuselage acting downwards in the centre, impose a bending moment on the wing. 
 
Maximum taxi weight (ramp weight)
• This is maximum permitted weight of the aircraft at which it may be
moved, either using its engines or being pushed or towed.
• MTXW includes MTOW and Taxi Fuel.  
  
Basic Weight (BW)
• This is the weight of the aircraft prepared for service and includes the actual weight of the aircraft including its fixed equipment, 
unusable fuel and configuration equipment with galley structures.
• Basic Weight (BW) is published:
⇒ on sheet C3 of IATA AHM560,
⇒ in aircraft weighing report stored in cockpit documents.  
 
Dry Operating Weight (DOW)
• Dry Operating Weight consists of:
⇒ Basic Weight (BW),
⇒ Crew weight,
⇒ crew baggage,
⇒ pantry weight,
DOW = BW + CREW + CREW BAG + PANTRY
Fuel ballast, if carried, should be included in DOW  
 
Operating Weight (OW) 
The Operating Weight of an aircraft consists of:
• Dry Operating Weight
• Take-off Fuel
 
Deadload
The deadloads is the total weight of the following items:
• Passenger's checked baggage (BAG or BT, BC, BY)
• Cargo (CGO or C)
• Mail (M)
If loaded in Unit Load Devices, the weight of the ULDs is also added to the deadload.
 
Traffic Load (Payload)
Allowed Traffic Load (maximum traffic load)
The Allowed Traffic Load is the maximum load capacity (weight) that may be accepted on a flight. It depends on the structural
and operational maximum weights of an aircraft and on the quantity of fuel needed for a flight.
 
Total Traffic Load (actual traffic load)
• Traffic Load consist of following weights:
⇒ passengers
⇒ baggage,
⇒ cargo including non-revenue load as: EIC, CSU, ballast carrying in holds, empty ULD weight, 
⇒ mail
⇒ non-revenue load as EIC, THS, ballast carrying in holds, ULD empty weight (treated as cargo) 
TTL = PAX + BAG + CARGO + MAIL  
 
The Total Traffic Load consists of:
• Passengers (PAX)
• Deadload
 
Underload
The Underload is the difference between the Allowed Traffic Load and the Total Traffic Load.
Allowed Traffic Load - Total Traffic Load = Underload
Underload is the weight that still is available until the limiting maximum weight is reached.
 
Block Fuel
The Block Fuel is the TOTAL amount of fuel on board before starting engines.
 
Taxi Fuel
The Taxi Fuel is the amount of fuel used from time of engine start and taxiing until the aircraft has reached the take-off point.
The Taxi Fuel has been standardized each aircraft type, with exception for certain airports.
 
Take-off Fuel (TOF)
Weight of the fuel on board when the aircraft releases the brakes for take-off.
Block Fuel - Taxi Fuel = Take-off Fuel
 
Trip Fuel (TIF)
The Trip Fuel is the weight of the precalculated fuel consumption from brake release to touch-down at the next intended landing point.
 
Burn off Fuel
The Burn off Fuel is the fuel that has been burned. It's the sum of Taxi and Trip fuel.
 
Reserve / Remaining Fuel
The Reserve Fuel is the quantity of fuel left in the tanks after touch-down at the intended landing point. It consists of contingency
(to cover deviations due meteo, routing, flight levels), alternate (to reach the alternate airport), company (for specific operational
requirements, e.g. approach procedures), final reserve, additional and extra fuel (amount taken at the commanders's discretion).
 

COG LOCATION – UNITS SPECIFICATION

BI BASIC INDEX - index at Basic Weight 
DOI DRY OPERATING INDEX - i ndex at Dry Operating Weight
DLI DEADLOAD INDEX - index at cargo compartment loaded
DLMAC DEADLOAD MAC - % MAC at cargo compartment loaded
LIZFW LOADED INDEX at ZERO FUEL WEIGHT - index at ZFW
MACZFW % MAC at ZERO FUEL WEIGHT - % MAC at ZFW
LITOW LOADED INDEX at TAKE OFF WEIGHT - index at TOW
MACTOW % MAC at TAKE OFF WEIGHT - % MAC at TOW
LILAW LOADED INDEX at LANDI NG WEIGHT - index at LAW
MACLAW % MAC at LANDING WEIGHT - % MAC at LAW  
 
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