ISO 21384-4:2025

Overview

ISO 21384-4:2025 - "Uncrewed aircraft systems - Part 4: Vocabulary" is the second edition of the ISO vocabulary for uncrewed aircraft systems (UAS). The document standardizes terms and definitions widely used in UAS science and technology, ensuring consistent language across industry, regulation, research and operations. This edition updates and expands the terminology to reflect evolving concepts such as BVLOS, eVTOL and UAS traffic management (UTM).

Key topics and definitions

This part of ISO 21384 focuses exclusively on clear, authoritative UAS terminology, including but not limited to:

• Operational terms: flight time, flight plan, flight route, operation plan, operational volume, geo-limitation
• Roles and crew: remote pilot-in-command (RPIC), remote co-pilot, remote crew member, RPA observer, aerodrome pilot
• Systems and links: command-and-control (C2) links, down-link, payload link, ATS communication link, CNS
• Safety and management: safety management system (SMS), safety assurance, safety risk management (SRM), operational risk management (ORM), in-time system-wide safety assurance (ISSA)
• Airspace and infrastructure: aerodrome, droneport, vertiport/heliport, segregated airspace, collision volume/boundary
• Aircraft classes and operations: RPAS, remotely-piloted, optionally piloted aircraft (OPA), eVTOL aircraft, model aircraft, BVLOS and EVLOS operations
• Support services and terminology: operation support service, external service, UTM service, service level agreement (SLA)

Note: the standard contains no normative references and is intended as a terminology resource to be used alongside regulatory and technical documents.

Practical applications

ISO 21384-4:2025 is a foundational reference for:

• Harmonizing terminology in regulatory frameworks and national aviation authority guidance
• Drafting operations manuals, flight manuals and safety documentation
• Developing UTM systems, flight-planning and C2 software where consistent terms reduce ambiguity
• Training curricula and certification materials for remote pilots and operational personnel
• Contracting, procurement and service-level agreements between operators and C2/UTM service providers
• Research papers, industry standards and cross-border cooperation where precise definitions matter

Who should use it

• National aviation authorities and regulators
• UAS and eVTOL manufacturers and integrators
• UAS operators, service providers (C2CSP, UTM) and droneport/vertiport planners
• Safety managers, SMS/SRM practitioners and training organizations
• Standards writers, legal teams, insurers and academic researchers

Related standards

• ISO 21384 series (other parts listed on the ISO website)
• ISO 23629-12 (referenced for safety management concepts in the document)

Keywords: ISO 21384-4:2025, uncrewed aircraft systems vocabulary, UAS terminology, RPAS definitions, BVLOS, eVTOL, UAS traffic management, droneport, remote pilot-in-command, safety management system.