When the internal audit activity lacks the necessary resources to complete the audit plan, the most appropriate action for the CAE is to ensure that the audit plan is still executed effectively and efficiently. Outsourcing some of the audits to the organization's external auditor, who is already familiar with the organization, can help mitigate resource constraints. This approach leverages the external auditor's knowledge of the organization, ensuring continuity and quality in the audit process, while allowing the internal audit function to meet its obligations and deadlines.
Reference:
IIA Standard 2030: Resource Management
IIA Practice Guide: Coordinating Internal Audit and External Audit