Technical Round Trip Delay

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The Technical Round Trip Delay (TRTD) is available from the DPMF Dashboards and is the time taken by the system to uplink a CPDLC message and receive its application level acknowledgement, which may be a LACK or an ERROR as illustrated below.

The dashboard shows the 95th and 99th percentile for the TRTD for the selected centre(s) or operator(s) against the equivalent values for all centres.


Technical Round-Trip Delay is measured using ground initiated transactions that require a LACK response. Only ground initiated transactions are considered to ensure that a common time source is used for both time measurements.

TRTD = First LACK/ERROR response reception time – Uplink message transmission time

Note: For FANS aircraft the gateway in the ground system generates a LACK when it receives a message delivery assurance report from the ACARS data services processor.