MCDU Anomalies

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747-400 MCDU

This section is only of interest for people who use the MCDU to have external access to PS1's CDU.

The data path between PS1's CDU and the external MCDU is complex. Halfway in the path, an Optical Character Recognition step takes place, to convert the PS1 true bitmap CDU image to ASCII strings. It turns out to be non-trivial to do this OCR, as PS1 works with a relatively coarse display resolution. It depends on the exact display position of a character whether it is six or seven pixels wide. This means that, despite Ivan's efforts to code the OCR as robust as possible, once in a while the OCR module misses a character.

The MCDU code contains a few specific correction rules for these known anomalies. It may very well happen that you detect some more consistent inconsistencies between the PS1 display and the MCDU display. If you can reliably reproduce these, please mail them to me!

For a good MCDU anomaly report, please include:

  • The PS1 page title, including the page number.
  • The PS1 display output, with line number (the whole page is not required). It is very important to me that you send the whole line, with spaces and everything. That's 24 characters per line.
  • The MCDU display output, in the same way as the PS1 display output.
I will then try to come up with a regular expression that matches and corrects the anomaly.

© 2021 Jeroen Hoppenbrouwers For more information, mail to