From Technical Receipt to Operational Closure: Acknowledgement-State Ambiguity in RPAS CPDLC Transactions

Remotely Piloted Aircraft Systems (RPAS) operation within controlled instrument flight rules (IFR) airspace exposes a potential limitation in existing Controller-Pilot Data Link Communications (CPDLC) transaction logic: the receipt by the aircraft end system of the message is not equivalent to the pilot's acceptance of the clearance. In conventional flight decks, receipt of the datalink instruction at the aircraft end system, cockpit presentation, flight crew awareness, and pilot response are tightly coupled. In RPAS operation, these processes occur sequentially in the aircraft, command and control (C2) relay, Remote Pilot Station (RPS), and Remote Pilot (RP), respectively. This paper presents a conceptual framework for identifying and monitoring this operational gap. Through a structured conceptual analysis of CPDLC transaction stages, Performance-Based Communication and Surveillance (PBCS) performance logic, RPAS C2 architecture, and RP-human factors, this paper proposes a five-state RPAS transaction chain: aircraft receipt, RPS delivery, RP awareness, RP response, and air traffic control (ATC) closure. The analysis shows that traditional metrics such as technical round-trip delay, Provider Abort (PA) rate, and logon success can confirm parts of the communication chain. However, they may remain blind to RPS message-display failure, delayed awareness, and workload-driven response omission. For this reason, the paper proposes monitoring extensions, such as RPS message delivery success, segmented transaction latencies, and granular Pilot Operational Response Time (PORT) reporting. These metrics are offered as supplements to current PBCS/Datalink Performance Monitoring Function (DPMF) performance measurement, not as substitutes. The framework contributes to understanding human–machine communication in RPAS operation.