Re: FMS capability (was: Re: AA965 proves Airbus bashers deadly wrong)

From: (Ed Hahn)
Organization: The MITRE Corporation, McLean, Va.
Date:         27 Feb 96 23:00:30 
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  or MIME structure (Petter Lorck) writes: (Ed Hahn) wrote:

   >Yes, assuming the computer had the information about terrain
   >available.  However, because of the (correctly) stringent nature of
   >certification rules, the FMS computers on board most equipped aircraft
   >have an upper limit of 1Mword of memory or less (i.e. 2MB), due to the
   >need to show that the electronics industry has experience with the
   >components to have REAL, demonstrated MTBF figures.

   Are you sure about that number (2MB)? I seem to recall that the
   capacity of the UNS 1B FMS is given at 5MB. But of course, now that I
   try to find that number in the operators manual I can't find it.
   Anyway, this is what is listed in the manual :
   The data base provides the FMS with information on over 100,000
   waypoints, navaids, airports and over 12,000 SIDs, STARs and
   Approaches. Additionally, the data base has the capability to store up
   to 200 pilot defined routes utilizing up to 3000 waypoints.

I'm fairly certain about the current capability of 1Mword, but am
unsure about the exact size of a word in a typical FMS implementation
(I'm pretty certain that they are using 16-bit words.)

Note that this would be Boeing/McDonnell Douglas FMS capabilities.
(The UNSunit may have a greater memory capability, due to the more
recent architecture of it's internals.)

In any case, the FMS does not have terrain data available to it, and
the current avionics industry development is leaning more toward
giving the GPWS a terrain data base, and to leave the FMS alone...


--------   Ed Hahn | | (703) 883-5988   --------
The above comment reflects the opinions of the author, and does not
constitute endorsement or implied warranty by the MITRE Corporation.
Really, I wouldn't kid you about a thing like this.