The method works on the principle of shaft horsepower (SHP) input into approximation formulas for fuel flow and emission factors. In combination with time and power modes for different flight segments and for different helicopter categories, emissions in the vicinity of airports and per flight hour can be estimated.
FOCA has developed the guidance on the basis of own helicopter engine emission tests in collaboration with the German Aerospace Center DLR, confidential engine manufacturer data, helicopter operation manuals and flight tests. The “Guidance on the Determinaton of Helicopter Emissions” describes all necessary elements for application of the method and their basis:
Based on the guidance, a table with estimated emissions per helicopter type is offered for download as well. The table contains all formulas and calculation steps (respective columns are faded out but can be faded in). Grey shaded cells are input cells. Green shaded cells indicate piston engine helicopters.
Caution: Despite the degree of detail in the FOCA method, which allows estimating emissions for individual helicopters, the practitioner must be aware of the fact that individual helicopter engine emissions characteristics are not taken into account to produce the results. A result gained with the estimation functions of this methodology and a result based on the knowledge of specific individual engine data may differ by a factor of 2 or more. For the same reason, it is not appropriate to use the method to compare helicopter emissions of different helicopters of similar size.