The UK is a signatory to the Chicago Convention which established the International Civil Aviation Organisation (ICAO). The UK, as a contracting state to that Convention, includes the Overseas Territories and so the obligations under the Convention also apply. These obligations include the adoption of Standards contained in the Annexes to the Convention. Further to this the UK has decided, as a matter of policy, also to adopt the Recommended Practices in the Annexes. To that end, ASSI is required under a Direction from the UK Government to produce requirements that give effect to ICAO Standards and Recommended Practices (SARPs), and the Air Navigation (Overseas Territories) Order and OTARs together are the means for achieving that.
There may be individual circumstances where it is not feasible to comply with a Standard or Recommended practice as reflected in the OTAR. In the case of aerodromes for example, due to the physical characteristics it may not be possible to implement a completely compliant slope on a small part of a taxiway. In these instances a case can be made to the regulator for an exemption from the Order or a deviation from the OTAR requirement. This must be supported by a safety assessment which reviews the risk of noncompliance and proposes mitigating measures where appropriate. An OTAC on Safety Assessments contains useful guidance on how to do this.