There are altogether three important “flexibility tools” in the process of the certification of aerodrome infrastructure and design. The establishment of an individual aerodrome Certification Basis (CB) includes the possible element of special conditions (SC), as described under ADR.AR.C.025 in annex II of Regulation (EC) No 139/2014. It gives the flexibility to the authority to allow deviations from the Agency’s Certification Specifications when the aerodrome is subject to topographical, physical or other limitations.
Additionally, the concept of the equivalent level of safety (ELOS), as described ADR.AR.C.020 (b) in annex II of Regulation (EC) No 139/2014, allows for technological solutions or alternatives to be introduced into the CB instead of complying with the applicable certification specification/s, under condition that the authority allows for an equivalent level of safety to be demonstrated. (see also the Agency’s Guidance Material for ADR.AR.C.020 and see also answer to question ADR4).
Furthermore, the concept and requirements introduced by Art. 7 “Deviations from certification specifications” of Regulation (EC) No 139/2014 allow competent authorities to accept “legacy” deviations from the certification specifications until the end of 2024. Such “legacy” deviations have to pre-date the coming into force of the said Regulation (i.e. have existed before 6 March 2014) to continue as long as they cannot be captured with the aforementioned concepts, are safety assessed, mitigated and undergo regular reviews to establish their continued legitimacy. Such acceptances may be formalised in what is called a Deviations Acceptance and Action Document (DAAD). (see also answer to question ADR5).