NAV ID is no longer updated for DME-only reception

For each radio, X-Plane provides two data refs for ID (morse code) read-out: sim/cockpit2/radios/indicators/navN_nav_id and sim/cockpit2/radios/indicators/navN_dme_id where N is 1..10 for the 10 nav receivers X-Plane has by default. This is what allows you to hear the correct DME ID of a Nav radio in DME hold mode, where these IDs differ. These datarefs have been available since X-Plane 11.35. If you have not started using the DME_id datarefs, you are already not supporting DME hold functionality.

Starting with X-Plane 12, the nav_id datarefs will (correctly!) no longer reflect reception of stand-alone DMEs, and DMEs that are part of TACAN stations with no associated civilian VOR. Tuning a standalone DME will now only cause the navN_dme_id datarefs to show the ID, but not the navN_nav_id. This is important if you show the ID readout on the ND for bearing pointers. In this case, you will probably want to hide or park the bearing pointer and only display DME readout. Check the POH/FCOM of the airplane you are modeling for specifics.

Example: Tuning 108.50 at Paderborn airport (EDLP). This will cause the Paderborn/Lippstadt DME to be picked up. “PAD” will be displayed on nav1_dme_id but not nav1_nav_id, which will remain blank, along with the CDI remaining flagged as there is no VOR associated with that DME.

NAV radios can be used to pick up TACAN Azimuth with the new TACAN tuning datarefs

You might have noticed that in X-Plane 11.50, you can tune TACAN stations from the X-Plane map. For X-Plane 12, we added the datarefs for tuning TACAN conveniently using mode and channel. All 10 navigation radios can now be tuned to TACAN stations using the datarefs sim/cockpit2/radios/actuators/tacN_channel and sim/cockpit2/radios/actuators/tacN_mode, where N is 1 or 2 for the default radios. You can also use the array datarefs to access N=0..9. “Channel” is an integer between 1 and 126 inclusive. “Mode” is either 0 if the radio is operating as a VOR receiver (this is the default), or 88=’X’ or 89=’Y’ for a TACAN mode. Writing to these datarefs will cause the receiver to operate in TACAN mode, while writing to the frequency datarefs will cause the receiver to operate in VOR mode. Reading datarefs is always safe and does not change the mode of operation.

Example: Set 85X (channel=85, mode=’X’) near Pope AAF (KPOB). This will tune the Pope TACAN and give you Azimuth and distance information. This is the correct way to tune the TACAN for a military radio. A civilian radio would instead tune the paired frequency 113.80 using the frequency datarefs. This will cause you to only have DME, but not Azimuth.

Radio power is important when using a NAV receiver in TACAN mode: By default, the radio is powered on in receive-only mode and will not interrogate DME stations. You will only see the azimuth, not the distance. In real military applications, this is used to keep the plane under EMCON. You have to explicitly select transmit/receive (T/R) mode if you want to send out signals to interrogate DME stations and get a range reading:
sim/cockpit2/radios/actuators/nav{1,2}_power 0 = Off, 1 = R, 2 = T/R. If operating in VOR mode (civilian frequency rather than military channel), this restriction does not exist and a power dataref value of 2 has no meaning.

NAV1 and NAV2 are multi-mode receivers

The receivers for NAV1 and NAV2 can supply GLS FAS guidance like a localizer and glideslope when tuned to a GLS channel between 20000 and 40000 and near a GBAS ground station. By simply writing the channel number to the frequency datarefs sim/cockpit2/radios/actuators/nav1_frequency_hz or sim/cockpit2/radios/actuators/nav2_frequency_hz (or the array dataref at indices [0] and [1]) the virtual localizer and glideslope of a GLS approach can be presented regardless of the load status of said approach in the FMS. Note that this only works for GLS approaches and not for any type of SBAS approach (WAAS, EGNOS, MSAS). These can still only be picked up by the augmentation receivers (array index [10] and [11]) which must be auto-tuned by the GPS or FMS.

SBAS (WAAS) is a privilege

In order to equip your plane with an SBAS receiver (which can receive WAAS, EGNOS and MSAS), go to the Plane Maker Systems page and open the Electrical bus configuration tab. Assign the SBAS receiver a bus (or multiple) to enable it to draw power from the electrical system. Note you probably don’t give it an amperage. The power consumption of a GPS unit does not change appreciably whether its SBAS portion is off or on. Therefore, if you have already set the power consumption of your whole GPS system in amps, the amps for the SBAS receiver portion should likely remain 0 or a nominal 0.1.

For basically all modern general aviation aircraft, you should simply assign the same busses as the primary GPS.

On airplanes equipped with this capability, upon loading an approach with LP or LPV minima, sim/cockpit2/radios/actuators/nav_frequency_hz[10] and [11] will be auto-tuned to a WAAS or EGNOS channel and present FAS guidance for an LP or LPV approach.

Note that surprisingly few airliners do have SBAS capability. It is not standard on any Boeing aircraft and only very recently a retrofit for the 737 was certified. For Airbus, it’s called ‘SLS’ and is available as an option that currently only exists in the A350 and A320NEOs of the 2020 or later model years. So it is highly unlikely that you need to set this if you are making a commercial airliner that represents the current fleet standard. Do NOT confuse this with the GBAS receiver, which is far more common in airliners. GBAS reception is not influenced by this setting.

Note that failing the SBAS receiver in flight will yield slightly different behavior than not installing it in the plane in the first place.

Baro VNAV no longer unflags the WAAS glidepath

sim/cockpit/radios/gps_has_glideslope and sim/cockpit/radios/gps2_has_glideslope have erroneously indicated 1 in the past when flying an RNAV approach with baro VNAV. This is no longer the case, these datarefs will show 1 only for SBAS and GBAS derived glide paths, not for barometric path deviation. Use the barometric flight plan target altitude sim/cockpit2/radios/indicators/fms_fpta_{co}pilot dataref to find out whether barometric VNAV is active. This dataref is parked at -1000 if no baro VNAV is available.

Note: This does not apply to aircraft equipped with integrated approach navigation. If IAN is active, the baro VNAV path will be available as glide path read-out.

Glideslope can be selected off

The glide path receiver normally automatically tunes the UHF frequency paired with the VHF LOC frequency that is selected on the NAV receiver. This can be selected off, if you explicitly want to de-select the ILS glideslope, for example to fly a LOC approach with baro VNAV guidance. The array dataref sim/cockpit2/radios/actuators/nav_receiver_glideslope_off[N] defaults to 0 for all 10 radios, which means they can pick up glide slopes. Set the dataref to 1 for a specific radio to disable glide slope reception.

NAV1 and NAV2 can be restricted to ILS+GLS

On some modern airliners, the receivers for localizer and VOR signals are split in such a way that the autopilot can only follow a localizer, but not a VOR deflection. In that case, the NAV signal can be presented on the navdisplay, but the ILS signal is received by a distinct receiver which is the only one with a connection to the autopilot. This setup can be selected in Plane Maker on the Systems page which allow autopilot configuration, by ticking the checkbox “ILS/Multimode receiver only”. This changes the behaviour of the NAV receivers as follows:

  • NAV1 and NAV2 can no longer pick up a VOR signal. They will only un-flag for the reception of an ILS or GLS localizer.
  • NAV1 and NAV2 remain the only ground-based navigation that can be selected to the HSI and thus the only ones that the autopilot can follow in NAVLOC or APP mode.
  • NAV1 and NAV2 will be displayed on the default navdisplay in APP (0) mode.
  • NAV3 and NAV4 (array indices [2] and [3]) will be displayed on the default navdisplay in VOR (1) mode.
  • NAV3 and NAV4 (array indices [2] and [3]) are considered the VOR receivers of the airplane when loading a VOR from the map or instructor station.

Use NAV receiver power to “park” receivers

The array dataref sim/cockpit2/radios/actuators/nav_power should be used to “park” needles that are de-selected, as it also works with receivers NAV3-NAV9. Do NOT write invalid frequencies, like -1 or 999 to a frequency dataref. The frequency datarefs are range-checked for valid TACAN, LOC, VOR or GLS VDB channels and writing a “magic value” like -1 will cause a range check to trip. If you want a receiver to not display anything, simply un-power it.