In normal VOR/ILS/DME operations, one of the six DME channels is paired with the active frequency
and another with the preset frequency. Pressing the DME function key will split the NAV box on the
main tuning page, allowing the active DME channel to be selected from the active VOR/ILS
frequency. Cycling the DME select button sequences the NAV window from normal; to VOR/ILS, and
DME split tuning; to VOR/ILS and TACAN channel split tuning; back to normal. When the NAV
window is split, an amber H (hold) appears in the lower DME window and on EFIS. This H indicates
that the distance display (DME or TACAN) is not paired with the VOR/ILS navigation data. When the
H is displayed, the other aircraft systems HOLD annunciators will also illuminate. Display of the DME
(or TACAN) channel being held provides a more positive identification of the navigation channel. In
addition, the DME station identifier is also displayed. DME indicators are displayed on the MFD and
PFD's when SRN is selected on HSI.
Each DME has the capability to scan six channels, simultaneously tracking four selected DME
channels for distance, ground speed and time to station, as well as tracking two stations for
identification (IDENT) functions. Of the four channels of which it can track three functions (DIST, GS
and TTG), two are dedicated to the flight management system(s) (FMS).
Normally, one DME station will be tuned to an active VOR frequency, which is annunciated on the top
line of the NAV tuning window of the radio management unit (RMU). Another (preset) VOR frequency
may be selected in the preset frequency window. When a frequency is set in the preselect window,
the system will already be tracking the preselected station so that there will be no delay when that
frequency is transferred to active.
NAV tuning, which normally also selects the associated DME frequencies, is discussed under VHF
NAV in this section. Special tuning procedures applicable to DME, which are in addition to the NAV
tuning, are discussed below.
The DME has a "split tuning" mode which operates somewhat like conventional HOLD functions, but
provides other options. Pressing the DME button on the bottom of the RMU will divide the NAV
window into two windows. The top window will remain the active VOR frequency. H will be
annunciated on the bottom line, indicating that the DME frequency is holding with the active
frequency which is displayed on the top line. The bottom line will be labeled DME and will have in it
the active frequency displayed in VHF (VOR) format. The DME may then be tuned by pressing the
line select key and changing it to a new channel. Pressing the DME button again will cause the DME
(lower) window to change to a TACAN channel presentation. TACAN channels, along with their
related W, X, Y, and Z channelization nomenclature will then be tunable with the tuning knobs. The
DME function of all 126 TACAN channels may be tuned. No azimuth information is received in this
mode. A third press of the DME button causes the NAV window to return to its normal active/preset
presentation and the DME will resume tuning with the active frequency.
DME information is selected for display on the pilot’s and copilot’s PFD's by using the PFD menu on
the MFD.
AUDIO CONTROL PANELS
Two identical Honeywell Primus II digital audio control units are installed. Digital transmission of
audio from remote units to the audio panels differs from conventional audio systems in that it
requires one twisted pair of wires rather than many twisted pairs to achieve the same performance.
The control units are mounted on the pilot’s switch panel and the copilot’s meter panel respectively.
Cessna Citation XLS - Instrumentation & Avionics
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