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All MCDUs (and other screens) I've seen share a very similar, if not identical, set of fonts - a monospaced, sans-serif, very clean and easily readable font, often in two vertical sizes at the same horizontal pitch. What font is that? Do different instrument/airplane makers have their own? Do airlines standardize on one across their fleets?

FAA's Advisor Circular 25-11b (https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC_25-11B.pdf) makes some recommendations on fonts.

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My guess is that these are raster (non-scalable) fonts without any special name.

At least initially, the screen resolution wasn't (and needed not be) particularly high, and the characters were the typical 8x8 pixels or only slightly better. Such fonts are drawn by hand (by pixel) and don't have too many variations to speak about. (Although the sales people might disagree).

Later models with higher-resolution screens probably modeled the same terminal-type font to keep commonality. I still doubt MCDUs have an operating system (if any) with scalable font support.

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  • $\begingroup$ It sure looks like something in that direction. The AC I mentioned does recommend 5x7 and 7x9 as minimum pixel sizes for text and some Rockwell Collins units I've seen definitely are in the low pixel count field, with what looks like 7x9 characters for small sizes, but newer models appear to have anti-aliasing. Garmin units look, definitely, retro in comparison. $\endgroup$ – rbanffy Oct 22 '18 at 10:08
  • $\begingroup$ @rbanffy, interestingly, Garmin is probably in the same boat. Even in their newest glass systems (G2000 and G3000), they kept the same screen resolution as in G1000 (1024x768), and it applies to all sizes, from 10" to 15". $\endgroup$ – Zeus Oct 22 '18 at 23:22
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MCDUs date back to the first generation FMS that was developed in the late '70s for the B757/B767 aircraft. An equipment Characteristic for the MCDU was developed by ARINC committee and published as ARINC 739. This was replaced by ARINC 739A in the '90s to support additional new features.

The ARINC 739/739A Characteristics do not specify a particular font. The regulatory agencies (e.g., FAA) don't really care as long as it is easily readable and fault tolerant. That last bit is the concern that a dead pixel/row/column in the display causes a character to be misinterpreted.

Starting with the originals, the MCDUs were limited by the technology of the displays. They settled on a 14 line, 24 characters per line (fixed pitch) CRT display. CRT fonts were raster generated. The text layout carries over to the current MCDUs when they switched to LCD displays in the '90s.

The fonts used were limited by the CRT technology and later by the available number of pixels in the LCDs. The constraints of aircraft certification generally means that things don't change unless there's a compelling (think: money) reason to do so. So even with today's high resolution displays, the MCDUs still have a 14 line 24 character layout. With more pixels, the fonts are just higher resolution versions of the older fonts.

In recent discussions concerning displays, the manufacturers want a consistent look within the cockpit, subject to the certification rules. As you found in AC 25-11B, there's some general guidance:

5.4.3 The choice of font also affects readability. The following guidelines apply:

5.4.3.1 To facilitate readability, the font chosen should be compatible with the display technology. For example, serif fonts may become distorted on some low pixel resolution displays. However, on displays where serif fonts have been found acceptable, they have been found to be useful for depicting full sentences or larger text strings.

5.4.3.2 Sans serif fonts (for example, Futura or Helvetica) are recommended for displays viewed under extreme lighting conditions.

In my experience, Futura seems to be the most commonly preferred but others do come up. Not surprisingly, some fonts are copyrighted and are subject to licensing fees which reduces their popularity.

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  • $\begingroup$ Thanks. With your info, I was able to locate what looks like a first-gen system with pictures at 737b.blogspot.com/2013/06/flight-management-computer-fmc.html. $\endgroup$ – rbanffy Oct 22 '18 at 12:58
  • $\begingroup$ Me feeling, from Boeing's display and others, is of a monospaced format, somewhat close to OCR-B. Futura is a proportional font and suffers from readability issues in small sizes, but I get where you are coming from - it's a very clean design. $\endgroup$ – rbanffy Oct 22 '18 at 13:16
  • $\begingroup$ You are correct in assuming that monospaced fonts are still common. Boeing and Airbus tend to be very conservative about changes in the cockpit as airlines don't pay for anything they don't need. The high end bizjets tend to have more innovation in design as the customers are more interested in the tech. $\endgroup$ – Gerry Oct 22 '18 at 15:50
  • $\begingroup$ If the MCDU is 14x24 characters, a monospaced font makes sense. It's a bit curious, as the font size changes, but the grid remains the same and the spacing between characters varies. $\endgroup$ – rbanffy Oct 22 '18 at 21:16
  • $\begingroup$ That's the way most computer terminal displays operated until they shifted to graphical displays in the '80s (the first IBM PC display was 25 lines by 80 characters.) While you could fit more characters on a line when using the small font, they don't to simplify the display management. The MCDU is a dumb terminal. The remote app (FMS, Datalink, etc.) just sends the character strings to the MCDU where they will stay until they are overwritten. Miscount your string length and you leave stray characters on the screen. $\endgroup$ – Gerry Oct 23 '18 at 12:00

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