Overview
ISO 21384-4:2020 - "Unmanned aircraft systems - Part 4: Vocabulary" is an ISO standard that defines commonly used terms and definitions for unmanned aircraft systems (UAS). Its primary purpose is to establish a consistent, internationally accepted vocabulary for the UAS community-covering drones, remotely‑piloted aircraft, remote pilot roles, control links, airspace concepts and related operational terms. This vocabulary supports clear communication across regulation, design, operations, safety cases and research.
Key topics
This part of the ISO 21384 series focuses on terminology rather than prescriptive technical requirements. Key subject areas and illustrative terms included are:
- Aircraft types and categories: aeroplane, airship, manned aircraft, unmanned aircraft (UA/RPA), optionally piloted aircraft (OPA)
- Operational concepts: aerodrome pilot, flight duty period, operational volume, geo-limitation, aerodrome/ droneport
- Pilot and crew roles: remote pilot, remote pilot-in-command (remote PIC), remote crew member, RPA observer
- Flight modes and ranges: visual line‑of‑sight (VLOS), extended VLOS (EVLOS), beyond visual line‑of‑sight (BVLOS)
- Communication and control: command and control (C2) link, ATS communication link, payload link, radio line‑of‑sight (RLOS), down-link, up-link
- Safety functions and equipment: detect-and-avoid, airborne collision avoidance system (ACAS), collision boundary/volume, collision avoidance threshold, flight termination system, flight recorder
- Operational documentation and oversight: operations manual, operating manual, maintenance programme, qualified entity (QE)
Practical applications
Although ISO 21384-4 does not set performance or design requirements, it provides essential value by:
- Enabling consistent terminology in regulatory texts, certification paperwork and airspace integration policy for UAS
- Standardizing language used in manufacturer manuals, operations manuals, and maintenance programmes
- Supporting interoperability and safety analysis by ensuring engineers, operators and ATM (air traffic management) stakeholders use the same definitions for C2 links, BVLOS, detect-and-avoid, etc.
- Helping training organizations, legal teams, insurers and researchers draft clear contracts, safety cases, incident reports and academic papers
- Assisting international collaboration by aligning terms across national authorities and standards bodies
Who uses it
Key users include national aviation authorities, UAS manufacturers, operators (commercial and research), air navigation service providers, standards developers, training organizations, and technical writers preparing manuals and regulatory submissions.
Related standards
ISO 21384-4 is part of the ISO 21384 series prepared by ISO/TC 20/SC 16 (Unmanned aircraft systems). For related terminology resources see the ISO Online Browsing Platform and IEC Electropedia.
