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Computer-Related Incidents with Commercial Aircraft

Integrity of Navigation Data Used in FMS's

The final report on the Cali accident cited as one of four `contributing factors' to the accident the `FMS-generated navigational information that used a different naming convention from that published in navigational charts'. Recommendations 1 and 7 (of 17) to the FAA concern possible differences between authoritative navigation information and the use of this information in Flight Management Systems (FMS's). Recommendation 3 (of 3) to ICAO suggests to `Establish a single standard worldwide that provides an [sic] unified criteria for the providers of electronic navigational databases used in Flight Management Systems'. Jeppesen has responded to this report with specific Changes to NDB Navaid Identification in [Jeppesen] NavData [Database] (http://www.jeppesen.com/cali06.html).

National authorities supply navigational information to five industry data suppliers (Jeppesen, Racal Avionics, Aerad (British Airways), Swissair and GTE Government Services), which then supply this information to the almost twenty manufacturers of FMS's, many of whom have many different models. There is some concern about quality control in implementation of this data in FMS's. Although there is a standard, ARINC 424 from the industry/user group ARINC, which is `loosely followed' by the industry, this standard has no regulatory force and is not connected with any regulatory process. Shawn Coyle, of Transport Canada's Safety and Security division, has written a working paper, Aircraft On-Board Navigation Data Integrity - A Serious Problem, assessing the situation. It is not good. Coyle's argument is that FMS's are proliferating; that soon they will be used as primary navigation devices as GPS approaches come into use (they are advisory devices only at the moment - other avionics are the primary navigational devices); that they will therefore be used for precision instrument approaches, in which integrity of data is vital; and that there is no regulatory oversight into the integrity of the data used by these devices, nor into the process by which the data is implemented or updated in the FMS. Coyle gives eight examples in which nav data implemented in an FMS leads an aircraft to fly a profile different from the published procedure. Coyle says that Transport Canada is the first organisation to have systematically identified the problem.


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