User's Manual

UniLink UL-800/801 FANS
SCN 30.X
Operator’s Manual
23-20-06.02 45
December 2011
LATENCY
Upon CPDLC connection, the CDA (ATC) may send a FREE-TEXT
uplink with the desired message latency value. Latency may be reset
by the crew to the ATC-specified value. Upon hand-off to a different
ATC, a new value request may be received. The request will be in the
form of SET MAX UPLINK DELAY VALUE TO [value] SECONDS or
CONFIRM MESSAGE LATENCY TIMER OFF.
To change the LATENCY value:
1. Press LATENCY, LSK [4R].
2. Using the numeric keys, type in the desired value (can be set to a
non-zero value between 1 and 999).
3. Press [ENTER].
To turn off the LATENCY function:
1. Press LATENCY, LSK [4R].
2. Press the [BACK] key.
3. Press the [ENTER] key. The field will show –SEC to indicate
LATENCY is turned off.
Received CPDLC uplinks can have an optional SENT timestamp
appended to the message (at ATC’s discretion). The message latency
value is used by UniLink to determine if a received uplink is delayed
by comparing the sent time to the system time at which the uplink was
received. The delayed status of a given message is displayed
following the message text (example):
2211Z KZAK¨ NEW
PROCEED DIRECT TO NUCAR
(SENT 2205Z – DELAYED)
The time stamp that follows the uplink ATC message will include the
word DELAYED (“SENT 1234Z--DELAYED”). The crew may decide to
respond to the uplink normally or to contact ATC for clarification.
UniLink resets the message latency value to the default value stored
in the configuration module whenever the aircraft is without a CPDLC
connection such as end of flight, commanded termination, etc. The
latency value is not automatically reset during a CPDLC handoff.