How to improve VHF Data Link (VDL) Mode 2 connectivity
Effectivity: Global 5000 GVFD/6000/5500/6500/7500/8000 and Challenger 300/350/3500/605/650 aircraft equipped with datalink option
ATA: 23-22
By: Lahcene Bensalem and Sylvain Cuerrier, Technical ServicesThe datalink messages are managed by the Radio Interface Unit or Communication Management Unit (RIU-40X0/CMU-4000) and typically transmitted over VHF network or Satcom network. The VHF datalink is based on VHF Digital Link or VHF Data LINK (VDL) which consists of two subnetworks:
VDL Mode 0/A is analog VHF ACARS, also referred to as Plain Old ACARS (POA) with transmission rate of 2400 bits per seconds (bps)
VDL Mode 2 (VDL M2) is the second-generation VHF Datalink system, also designated as ACARS-Over-AVLC (AOA), AVLC (Aviation VHF Link Control) being the Datalink layer of the VDL-M2 protocol, which operates at a data rate of 31500 bps (13 times faster than POA media)
For Future Air Navigation Systems (FANS1/A+), media preference is given first to VHF VDL M2, then VHF POA, then SATCOM. This applies to the Aeronautical Telecommunications Network Base 1 (ATN-B1) and uses VHF VDL Mode 2 only. The VDL M2 is required to support Controller/Pilot Data Link Communications (CPDLC) for ATN-B1 in European airspace and for FANS1/A+ in U.S. Domestic En Route.
Datalink Recommended Configuration
The aircraft datalink system is, most of the time, configured with one or more VDL Datalink Service Providers (DSPs), mainly ARINC or SITA. One of these is designated as the “Preferred” DSP and will use this “Preferred” when available. At periphery of coverage, where VDL signals are weaker, it may result in switching between ARINC and SITA. As well, the system may switch from VDL M2 to POA or to Satcom, resulting in most cases, the CPDLC session being terminated.
Based on service experience, it is recommended that the operator use either "ARINC Only" or "SITA Only" configuration in regions where both ARINC and SITA have coverage. This will allow forbetter VDL CPDLC connectivity and seamless handoffs.
The "ARINC Only" configuration eliminates SITA, while the "SITA Only" configuration eliminates ARINC. The other regional VDL Mode 2 service providers, such as AVICOM-JPN and BRAZIL, may optionally remain enabled in either configuration. For additional details, refer to Collins Aerospace Service Information Letter (SIL) RIU-4000-25-2 (Publication No. 523-0837032), available on the “My Bombardier” portal.
Manual Selection of VHF Datalink Mode 2:
In addition, the flight crew has the ability to check the connection mode and manually select VDL M2, if switched back to VHF POA or disconnected.
The flight crew can also monitor the VHF VDL connection status from LINK STATUS menu. This page can be accessed via the TECHNICAL prompt on the DATALINK MAIN MENU page or via the AOC MAIN MENU page 2.
With the VHF set into DATA mode, the Link status will be as follows:
Connected via VDL M2, the VHF is in “AOA COMM” state (see figure 1).
Connected via VDL M0/A, the VHF state will indicate “POA COMM” (see figure 2).
NOTE:
Figures are examples from Global 7500, however the menu is fairly similar between other platforms.
It may happen that VDL M2 connection is lost. In this case, the flight crew can select the “MANUAL VHF TUNE>” prompt and then select “*VDL MODE 2”.
NOTE:
The “MANUAL VHF TUNE>” prompt might not necessarily be available when the VHF is in “AOA COMM” state.
For more details, operators may refer to the Collins Aerospace Operators Bulletin OPSB 0236-23 (Publication No. 523-0835726) Rev. 02 or the later version – “How to manually select VHF Datalink Mode 2 – if disconnected from KUSA”. This document is currently available on the Collins Aerospace Portal.
NOTE:
Although the applicability shown in the current OPSB initial issue doesn’t include RIU-4010/CMU-4000 Part Numbers that are applicable to Bombardier, the content of the document is indeed applicable to all our aircraft equipped with the Collins datalink system.
Bombardier is currently working to update the Aircraft Maintenance Manual (AMM)/Aircraft Maintenance Publications (AMP) with this preferred datalink configuration. Furthermore, Bombardier is also evaluating a Flight Operation Notification (FON) to provide flight crew work around in cases of the CPDLC end of session or disconnected associated to OPSB 0236-23.