Collins Aerospace GNSS - EASA Safety Information Bulletin (SIB) No. 2024-03R1
Effectivity: Challenger and Global aircraft
ATA: 34-55
By Stephane Beauchamp – Avionics, Technical Services The EASA (European Union Aviation Safety Agency) released SIB No. 2024-03R1 in February 2024 concerning incorrect processing of the integrity information message for Satellite Based Augmentation Systems (SBAS). This is applicable to Collins Aerospace Global Navigation Satellite Systems (GNSS) GPS-4000S receivers, part numbers 822-2189-100/-101, which may be installed on different Bombardier aircraft models.
As stated in the SIB, this potential safety concern is not considered to be an unsafe condition warranting an Airworthiness Directive (AD), and that does not warrant the issuance of an operational directive.
The condition was identified following the European Geostationary Navigation Overlay Service (EGNOS) ground system update performed in November 2023, which exposed this issue in affected Collins receivers. EASA is currently conducting a thorough investigation to assess the potential effect on navigation performance following the reception of integrity information message (Message Type 6 (MT6)), sent by the SBAS system for a specific value generated by the Issue of Data Fast (IODF) correction parameter. This message indicates a potential impact on the integrity of certain satellites.
Bombardier was recently advised by Collins Aerospace of this condition impacting the production for any new-built GNSS receivers, PN: 822-2189-101, due to the described condition and non-compliance with the Radio Technical Commission for Aeronautics (RTCA) DO-229 standard. Under some conditions and scenarios, the GNSS software uses the MT6 message out beyond a specified timeout period. It should be emphasized that no aircraft in service with PN: 822-2189-100/-101 have reported any related issues so far.
The corrective action is pending the certification of receiver PN: 822-2189-102 to address this condition. This condition does not impact repair, support and continued operation of the PN: 822-2189-100/-101 in service.
The current analysis shows that this condition is unlikely and has minimal impact on the accuracy of the position and, as such, would not affect Required Navigation Performance (RNP) operations in SBAS airspaces. The MT6 value will unlatch itself if other MT messages are received or the GNSS power is cycled.
The associated Flight Deck Effect (FDE) is indicated by the GNSS dropping from an SBAS to GPS navigation mode. More specifically, during a Localizer Precision Vertical (LPV) approach with a required higher integrity, the condition would generate the following messages (specific to aircraft variant and type):
Global Vision: LPV APPR or LPV amber on PFD and associated LPV NOT AVAILABLE FMS
Global 7500: LPV INVALID CAS
Challenger (all variants): APPR NOT AVAILABLE or LPV NOT AVAILABLE FMS
The ongoing investigation by Collins Aerospace and the certification authorities is focusing on the analysis of historical data for SBAS availability and integrity.
Once finalized, Bombardier will also perform its own assessment on the probability impact of the incorrect processing of MT6 messages, and whether any operational mitigations or limitations are necessary when operating under coverage of SBAS (including EGNOS).
For details on the SIB, please click here.