What's the type of screen used on the Boeing PFD and ND displays?

It doesn't seem to be LCD - because for one they didn't have them when these planes were certified and the resolution seems to be so good. Even better than a 4K LCD display.

I assume it's some type of CRT.

But how does one create text on a CRT with such high resolution - the text's are so clear even close up.

  • 2
    $\begingroup$ I am not familiar with the 737, but I can say the early Airbus CRTs were hybrid vector-raster CRTs. That is, when drawing lines and text, the e-beam traces the lines, so there are no pixels. When drawing fills, like the horizon, those are rastered. This was done for maximum brightness. Step through this YouTube video of an A300 to see how it's done. $\endgroup$
    – user71659
    Nov 30 '21 at 4:17
  • $\begingroup$ Yes that's my initial thought. When I look at the real display it looks like a crt (but it's not concave) - but the lines and text are very sharp. even up close (6 inches or so) - no pixelation. $\endgroup$
    – dashman
    Nov 30 '21 at 23:07
  • $\begingroup$ The reason why you aren't seeing a curve is that the DUs have a dark tinted piece of glass in front of the CRT tube, the same as the anti-glare filters people used to use on their computer monitors. Underneath, the actual tube has a curve and has a lighter gray background. $\endgroup$
    – user71659
    Dec 1 '21 at 1:14

As @mins indicated there are retrofit LCD displays available for the B737 Classic.

The 737NG series aircraft were initially certificated with CRT displays. As CRT technology became obsolescent and very quickly non-procurable in the late 1990's Boeing needed to address the issue for both existing aircraft and future production.

Rockwell Collins was the B737NG display system supplier and developed an LCD Display Unit (DU) to replace the earlier CRT DU. These became the standard production DUs about 1999 (less than two years after the NG's entry into service). As they were certificated in the aircraft, they were also available to replace the CRT DUs in earlier production aircraft.

There were concerns by the FAA at the time about mixing DU types on the flight deck. The solution was to replace all DUs with LCD DUs if one of the CRT DUs failed and there was no spare CRT DUs available.

A similar issue existed for the B747-400. Due the the different economy of scale, they made the effort to certificate the use of mixed display types. That was around 2001.

By 2002, the 737 Aircraft Maintenance Manual makes no reference to the CRT displays:

Display Unit

The display unit (DU) is a flat panel liquid crystal display (LCD) unit. The LCD makes a high resolution color image of the flight data.

  • $\begingroup$ I'd be curious to know what the resolution of these screens are (i.e. PPI). I've set up a sim display using a 4K display and I can still see the jaggies. The text and lines on these displays have no jaggies and super clear. $\endgroup$
    – dashman
    Nov 30 '21 at 1:13
  • $\begingroup$ @dashman Ultra-high resolution LCD displays have definitely been a thing since at least the late-1990s (for example, the truly epic IBM T221 from 2001 was a 22-inch display with a 204dpi display at 3840x2400 (slightly bigger than 4K). Back then, desktop computers really couldn't handle anything besides 96dpi, so there was no incentive for anyone to make mass-market high-DPI displays until Windows caught-up with macOS's Retina around 2015. I also remember reading about high-DPI medical X-Ray display monitors too. $\endgroup$
    – Dai
    Nov 30 '21 at 8:48
  • 1
    $\begingroup$ desktop computers really couldn't handle anything besides 96dpi No! They couldn't (except with special new video cards, as with the T221, etc.) handle such high total display sizes (3840x2400). But 96dpi? 2040dpi? Whatever! Windows (and most other OSes) can work with any size display. The issues are the number of pixels. To take an extreme - you can easily use a projector to get an 8' wide display - that might be on the order of 20 pixels per inch. No reason you couldn't go in the other direction too. All a matter of cost. $\endgroup$ Nov 30 '21 at 13:03
  • $\begingroup$ ok thanks guys...so to replicate that rez..i need to get a 20 inch or so 4k or close monitor. $\endgroup$
    – dashman
    Nov 30 '21 at 23:03
  • $\begingroup$ @manassehkatz-Moving2Codidact What I meant was that both Windows (and macOS) and the greater ecosystem of applications generally did not handle rendering DPIs other than 96dpi correctly: so UI element layout calculations would be all messed up. Things didn't improve until Vista. A well-built custom application (like avionics, of course) will be able to handle it, but you couldn't run MS Word or anything like that on it. $\endgroup$
    – Dai
    Dec 2 '21 at 5:32

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