Aviation Investigation Report A98H0003

Weight and Balance

  1. Weight and Balance Limitations
    1. Weight Limitations
    2. Balance Limitations
    3. Cargo Compartment Limits
  2. Aircraft Empty Weights
    1. Structure Weight
    2. Basic Empty Weight
    3. Basic Weight
    4. Dry Operating Weight
  3. Cargo Weight and Allocation
  4. Passenger Weight and Allocation
    1. Fuel Weight and Allocation
  5. Aircraft Loading Procedure
    1. Passenger Boarding Procedure
    2. Cargo Loading Procedure
    3. Load Sheets
  6. HB-IWF Weight and Balance Calculations Summary
    1. Weight Calculation
    2. Balance Calculation
  7. Final Load Sheet

Weight and Balance Limitations

Weight Limitations

HB-IWF (the occurrence aircraft) was to be operated within the following weight limits:

Table: HB-IWF Weight Limits

Item Weight (kg)
Maximum Taxi Weight 287 120
Maximum TOW 285 990
Maximum Landing Weight 199 580
Maximum ZFW 185 970
Maximum In-Flight Landing Flaps Weight[1] 200 940

Balance Limitations

The C of G limits given in the load index below are valid up to the maximum TOW with landing gear extended.

(See chart of "Actual loaded index ZFW - loaded index TOW.")

Lateral loading is restricted by a maximum unsymmetrical fuel load of 1 800 kg.

Cargo Compartment Limits

The MD-11 has five cargo compartments. The configuration used for SR 111 is Swissair unit load version 260, depicted below.

(See illustration of "MD-11 cargo compartments.")

Table: Cargo Compartments and Unit Load Version 260

Forward Compartment Aft Compartment
1 2 3 4 5
Station Location 506 812 1103 1521 1775 1964 2090
Maximum Capacity (kg) 11 104 15 443 13 480 6 768 3 402
25 401 15 876

Aircraft Empty Weights

Structure Weight

Swissair defines the structure weight as the weight of the aircraft including furnishings and loose equipment.

Basic Empty Weight

Swissair defines the basic empty weight as the combined structure weight and standard fluid weights.

The basic empty weight for HB-IWF (the occurrence aircraft) was as follows:

Table: HB-IWF Empty Weight

Item Weight (kg)
Structure Weight 129 701.7
Water 952
Hydraulic Fluid 179
Engine Lubricating Oil 137
Unuseable Fuel in Tank 562
Unuseable Fuel in Lines 276
Standard Fluid Weight 2 106.0
Basic Empty Weight 131 807.7

Basic Weight

Swissair's weight control system uses average basic weights for groups of the same aircraft type and configuration. HB-IWF was in the 131 925 kg basic weight group.

Dry Operating Weight

Swissair defines the dry operating weight as the basic weight plus operational items, including crew members, their baggage, and pantry items (e.g., galley, bar, food, and beverages). Swissair uses standard weights for crew members (90 kg each); the pantry weight is based on the style of pantry. SR 111 had 14 crew members and pantry code M.

The dry operating weight for HB-IWF was as follows:

Table: HB-IWF Dry Operating Weight

Item Weight (kg)
Basic Weight 131 925
14 Crew Members (90 kg each) 1 260
Pantry M 4 645
Dry Operating Weight 137 830

Cargo Weight and Allocation

The following cargo weights and allocations for SR 111 were provided by Swissair and verified during the investigation based on collected waybills.

Table: SR 111 Cargo Weights and Allocations

Compartment Position Cargo / Baggage Weight (kg)
(includes container weight)
Load Planner Calculations Investigation Findings
1 11 1 430 1 430
  12 790 804
  13L 1 065 1 064
  13R 642 642
  14L 870 870
  14R 734 734
Subtotal   5 531 5 544
2 21 1 355 1 372
  22 2 185 2 162
  23 3 005 3 007
Subtotal   6 545 6 541
3 31 2 850 2 766
  32 1 920 1 829
  33 750 714
Subtotal   5 520 5 309
4 41L 360 360
  41R 292 292
  42L 411 411
  42R 819 819
  43L 258 258
  43R 649 649
Subtotal   2 789 2 789
5 (Bulk)   740 744
Grand Total   21 125 20 927

Passenger Weight and Allocation

(See illustration of "Passenger sections.")

The tables below detail the number of passengers assigned seats in each section, the distribution of passengers by gender and age, and standard passenger weights used in load calculations.

Table: Passenger Summary from Passenger Manifest

Passengers by Section Passengers by Gender[2]
First Class 10 Male 174
Business Class 42 Female 39
Economy Class 161[3]    
Total 213 Total 213

Table: Passenger Summary from Post-accident Review

Passengers by Gender Passengers by Age
Male 125 Adults (12+) 210
Female 90 Children (2–12) 3
    Infants (<2) 2
Total 215 Total 215

Table: Swissair Standard Passenger Weights

Passenger Weight (kg)
Adults (12+) 84
Children (2–12) 35
Infants (<2) 0
Crew Members 90

Fuel Weight and Allocation

Allied Fuels fuelled the aircraft with Jet-A fuel while it was parked at the gate at 2340. The total fuel weight was as follows:

Table: SR 111 Total Fuel Weight

Tank Weight (kg)
Tank 1 18 450
Tank 2 27 550
Tank 3 18 350
Upper Aux 850
Tail 100
Total 65 300

The flight plan indicated that SR 111 would use 1 000 kg of fuel for taxi and 49 600 kg for the trip. The actual taxi fuel used, as recorded on the FDR, was 720 kg. The take-off fuel was estimated at 64 300 kg. The aircraft taxied with a total fuel load of 65 300 kg. A fuel density of 0.812 kg/L was used for SR 111 weight and balance calculations.

Aircraft Loading Procedure

Passenger Boarding Procedure

  1. When a passenger purchases a ticket for a flight, their personal information is recorded in the airline's reservation system, including whether the passenger is male, female, a child, or travelling with an infant.
  2. When the passenger checks in for the flight, the passenger is issued a boarding pass and assigned a seat.
  3. The passenger's seat number and weight category information (i.e., male, female, child, infant) is electronically transferred to the load planner's electronic worksheet.

Cargo Loading Procedure

  1. Approximately two hours before the aircraft is loaded with cargo, containers, or bulk (i.e., loose items), the load planner completes a preliminary plan for loading.
  2. Once the aircraft is ready to be loaded, the load planner provides the ramp personnel with a loading instruction sheet.
  3. Once the aircraft is loaded, the ramp personnel advise the load planner of the actual loaded positions of the containers and the number of bulk items.

Load Sheets

  1. During the cockpit preparation, the flight crew inserts the flight plan and preliminary load sheet figures into the FMS to get a complete flight plan calculation.
  2. The load planner inputs the data from the ramp personnel into the load control computer. The computer automatically calculates the C of G and operational weights for take-off based on the aircraft weight, the cargo weight, the passenger weight, and the fuel weight.
  3. Prior to pushback, the flight crew receives a printed final load sheet from the load planner via the ACARS.
  4. The flight crew examines the final load sheet and inputs the ZFW and the MACZFW C of G into the fuel initialization page of the aircraft's FMS using the MCDU. The actual TOW and the actual take-off C of G is then calculated by the FMS.

HB-IWF Weight and Balance Calculations Summary

Weight Calculation

The information provided by Swissair indicated that the actual dry operating weight was 137 713 kg. The cargo weight was calculated by Swissair as 21 125 kg. Calculations performed during the investigation indicated that the total weight of the cargo, including passenger baggage as determined by waybills and standard weights, was 20 927 kg. While the 198 kg difference in cargo weight could not be resolved using the waybills provided, this difference represents less than 0.1% of the TOW. From an aircraft loading standpoint, this difference is negligible. Swissair calculated the passenger weight by multiplying the standard weight of 84 kg by the total number of passengers, excluding infants. Calculations performed during the investigation determined the following weights:

Table: Weights

Item Weight (kg)
Dry Operating Weight 137 713
Cargo Weight 20 927
Passenger Weight 17 892
ZFW 176 649
Fuel Weight 65 300
Taxi Fuel –720
Gross TOW 241 112

The load control computer calculated the estimated TOW of SR 111 to be 241 147 kg. A detailed calculation performed after the occurrence revealed that the actual TOW was 241 112 kg. The 35 kg difference is negligible. Both weights are within the maximum structural limits.

Balance Calculation

The load control computer calculated the C of G to be 19.8% MAC. Using the balance table, the C of G was manually calculated to be 20.0% MAC. Both of these figures are well within the balance limits.

Final Load Sheet

(See copy of "Final load sheet.")

[1]    Limitation to prevent flaps from being overstressed when selecting landing flaps in flight at weights in excess of normal landing weights.

[2]    There is a difference between the Passenger Manifest and the Post-accident Review of the passengers by gender. This is attributed to the ticketing information. The passenger names were correct, but the gender was incorrect on the manifest. Gender information is used for weight calculations. Swissair used the same standard weight for males and females; therefore, the difference in the gender was inconsequential.

[3]    There were two infants who were not ticketed or assigned a seat, but who were included in the load control.

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