1 With regard to the annual interest rate set for assets required for operations, the following must be taken into account:
1.1 Assets required for operations are:
1.1.1 the residual procurement and/or manufacturing values of the existing plant, property and equipment which result after depreciation at the end of the fiscal year; and
1.1.2 operationally necessary net current assets.
1.2 The interest rate is calculated according to the weighted average cost of capital (WACC). The WACC is set at the level of the operating result after calculatory taxes and parafiscal charges but before interest (WACCs).
1.3 The WACCs is measured according to the following formula:

1.4 The individual parameters in the formula referenced under 1.3 are defined as:
1.4.1 EK = Equity
1.4.2 FK = Debt capital
1.4.3 ke = Cost of equity = rf + β ● (rM – rf*)
whereby
rf = Returns on secure investments: these are measured according to the average (arithmetic mean) of the monthly yields on 10-year Swiss government bonds over the previous 10 years.
β = Systematic, non-diversifiable equity risk: the airport's β is calculated on the basis of the average of the unlevered β (assuming an equity ratio of 100%) of the affected airport and at least 10 comparable airports. The selection of the comparison airports must be kept stable over time. When calculating the unlevered β for each airport, β is calculated as a linear regression over the previous 5 years of the monthly course of the rate of return of the share of the affected airport compared with the course of the of the rate of return of the most broadly based country-specific stock market index.
(rM – rf*) = Market risk premium: this is calculated as the difference between the average stock market return (rM) based on historic values and the return on secure investments (rf*). The average stock market return corresponds to the arithmetic mean of the annual return achieved on the Swiss stock market since 1926. The average return on secure investments corresponds to the arithmetic mean of the annual return achieved on Swiss federal bonds since 1926.
1.4.4 kf = Cost of debt capital = 
whereby
P = Debt capital risk premium: this is measured according to the average of the 10-year monthly spread between the yields on bonds with a rating corresponding to that of the airport and the yields on government bonds with the same term. The determination of the applicable rating is made by comparing the ratings of the comparison airports used to calculate β. If it can be demonstrated that the actual annual borrowing costs (costs of debt capital) during the charge period will be significantly higher than the borrowing costs estimated on a market basis according to the formula, then kf may be calculated on the basis of the actual borrowing costs.
1.4.5 s = Tax rate: this is determined as the 5-year average (arithmetic mean) of the ratio between annual tax expenses and annual pre-tax profits.
1.5 Capital structure (ratio of debt capital to equity): this is determined on the basis of the 5-year average of the market-value capital structures of the comparison airports used to calculate β.
2 Special circumstances in the sector not relevant to flight operations may be taken into account when calculating reasonable capital interest. The airport operator may modify the calculation as follows:
2.1 The operator may take account of existing special business and financing risks in the sector not relevant to flight operations.
2.2 The operator may apply an additional parameter when calculating reasonable capital interest in the sector not relevant to flight operations; this parameter takes account of the demonstrably greater expectation of returns of minimally capitalised companies (i.e. “size premium”). Calculation of the size premium must be based on best practices and data from recognised service providers.
2.3 Reasonable capital interest in the sector not relevant to flight operations may, in derogation from 1.1.1, be calculated on the basis of the market value of the clearly allocated assets. For this purpose, the book value of the assets is multiplied by the 5-year average of the ratio between the market value and the book value of the equity of the airport concerned or of comparison airports.