Note 20 - Critical accounting judgments and key sources of estimation uncertainty:

In applying the Company's accounting policies, which are described below, Management is required to make judgments, estimates and assumptions about the carrying amounts of assets and liabilities. Estimates and assumptions are based on historical experience and other factors considered relevant. Actual results could differ from those estimates.

Critical accounting judgments

Significant information on assumptions, critical judgments and uncertainty estimations recognized in the consolidated financial statements are as follows:

20.1	Revenue
20.2	Deferred tax assets and liabilities
20.3	Reserve for doubtful accounts
20.4	Commercial services revenues from leased locales
20.5	Useful life of the Airplan concession

20.1 Revenue

In accordance with Note 19.1.3, Management monitors and adjusts its revenue on a regular basis so that it does not exceed the maximum rate limits.

20.2 Deferred tax assets and liabilities

The Company recognizes deferred tax assets and liabilities based on the differences between the financial statement basis and the tax bases of assets and liabilities. In order to determine the basis of deferred IT, taxable income projections are prepared to evaluate whether the legal entity will be subject to IT.

The determination of the IT provision requires calculations and interpretation and application of complex tax laws. Those calculations are used to assess the period and method of recovery of favorable tax balances.

Management has determined deferred taxes based on approved tax rates that are in line with its expectation of the form of realization of such items. See Note 18.16. Management's expectation could be affected by the main detailed items described in Note 14.

20.3 Reserve for doubtful accounts

The Company carries out constant evaluations of the credits made to its clients and adjusts the credit limits based on the payment history of its clients as well as on the credit's current value. It continuously monitors collections and payments of its clients, thus preventing estimated credit losses based on its experience and losses from collection to the client that has been identified. Although those credit losses have been historically within expectations, as well as within the reserve created to prevent them, it cannot be guaranteed that the Company will continue experiencing the same credit losses that it had in the past. See Notes 6 and 18.7.2.

The Company conducts a sensitivity analysis to determine the degree to which possible changes to the assumptions used in determining whether or not the amount calculated of the reserve would be significantly affected. Management has concluded that percentage used to determine the reserve is the most sensitive assumption and therefore, if said percentage were to show an increase or decrease of 15%, it would have no significant effect, since this would represent Ps28 positive or negative in 2017 (Ps19 positive or negative in 2016).

20.4 Commercial services revenues from leased locales

Lease revenues are accrued monthly, and they are determined by applying a percentage on real sales revenues of the lessors (share) or a minimum agreed upon amount. Both are set forth in the respective lease agreements. The Company performs an estimate for the last days of the month to determine the monthly percentage of the share. Management compares the estimated bases with the real billing to conclude that there were no significant differences.

20.5 Useful life of the Airplan concession

The term of execution of the contract extends from the date of signing of the act of commencement of execution until the date on which one of any of the following events occurs:

· That the regulated revenues generated are equal to the expected regulated revenues, provided that by that time 15 years have elapsed.

· That 25 years have elapsed since the date of execution of the execution start certificate, regardless of whether, at the time, the regulated revenues generated have not matched the value of the expected regulated revenues.

· If the regulated income generated equals the expected regulated income before 15 years have elapsed from the date of execution of the certificate of execution, the duration of the execution of the contract will be, in any case, 15 years.

It must be taken into account, for purposes of the regulated revenues expected according to the definition of the concession contract, that the expected regulated revenue will increase once each of the complementary works (mandatory or voluntary) is delivered to the grantor.

The useful life for the amortization was determined as the duration of the concession and the amortization is calculated on a linear basis based on the years in which the recovery of the expected income of the financial model held by the Company is expected. The minimum term of the concession is the year 2015; however, in accordance with the complementary works carried out and the measurement of the expected income against the income generated, the concession will have a useful life until the year 2032.