3.3. Inaccuracy on initial data (DOW and DOCG)
3.3.1. Dry Operating Weight (DOW) definition :
a) DOW and DOCG definition policy
At delivery each aircraft is weighed to determine its Manufacturer‘s Empty Weight (MEW) and the Corresponding CG position. Using these values the operator can determine the aircraft Dry Operating Weight (DOW) and the corresponding CG position of each aircraft.
When defining the DOW and DOCG to be used in the loading and trimming documents the operator has two choices:
1.
considering each aircraft as independent so for each aircraft an individual set of values (DOW and DOCG) is set
2.
considering a group of aircraft as being part of one fleet so one single set of values (DOWfleet and DOCGfleet) is defined and used in the loading and trimming documents. As per aviation regulations a fleet of aircraft can be defined provided that, for each aircraft of the fleet, DOWaircraft and DOCGaircraft meet the allowed deviations to the fleet values :
A DOW maximum deviation of ± 0.5% of the aircraft Maximum Landing Weight
A CG position maximum deviation of ± 0.5% of the Reference Chord length
Note : in other words : an aircraft can be part of a fleet as long as DOWfleet – 0.5%MLW ≤ DOWaircraft ≤ DOWfleet + 0.5%MLW DOCGfleet – 0.5%Length of RC ≤ DOCGaircraft ≤ DOCGfleet + 0.5%Length of RC
Then during the aircraft life, between two weighings, its weight and CG position can be modified following maintenance tasks or cabin interior modifications, paintings. In that case the DOW and DOCG values used to enter the loading and trimming documents should be amended. As per aviation regulations the DOWdocument and DOCGdocument values amendment is mandatory as soon as
DOWdocument – 0.5%MLW ≤ DOWaircraft ≤ DOWdocument + 0.5%MLW DOCGdocument – 0.5%Length of RC≤ DOCGaircraft ≤ DOCGdocument + 0.5%Length of RC
b) Inaccuracy on initial data
In conclusion to the above statements, the DOW and DOCG assumed used in the loading and trimming documents is the aircraft one with a tolerable inaccuracy of ±0.5%MLW for the weight and ±0.5% of the Reference Chord length for the CG position.
. Ex: A320 in the following configuration:
MLW = 64 500 kg,
DOW = 39 400 kg
RC = 4.1935 m
The weight allowance is ±0.5 % of 64 500kg = ±322.5 kg
The CG position allowance is ±0.5 % of 4.1935m = ±0.0210 m
Then the aircraft weight and CG position can vary within the following values: DOWdocument - 322 kg ≤ DOW ≤ DOWdocument + 322 kg DOCGdocument - 0.021 m ≤ CG ≤ DOCGdocument + 0.021 m
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