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I've been going over the new Master Minimum Equipment List (MMEL) for Textron Aviation Model 500 Series Citations and on page 70 an Electronic Flight Information System (EFIS) 5 or 3 Tube System is mentioned but I can't find any information or pictures of it online.

Can someone explain?

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Look for the Honeywell Primus 1000 System.

Early systems were 5 tube - an EADI and EHSI for each crew plus an MFD (Nav/Wx display) as shown below:

Cessna with 5-tube display
source: swaviation.com

Later ones were 3 tube - 1 PFD on each side plus the MFD as shown below:

Cessna with 5-tube display
source: airliners.net

The symbol generators are shown in the MMEL as they have reversion capability. The 'tubes' or the actual displays would be listed under section 31 Indicating/Recording Systems but aren't included in the MMEL as they are always required.

Section 34 Navigation does allow for functional portions of the displays to be inop.

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If you look at the document you link, you'll see that the 5/3 Tube systems are not EFIS, but "Symbol generators for EFIS":

enter image description here

Looking for "Symbol generator for EFIS" I find the following:

A Symbol Generator (SG) is the device that receives the data from the airframe sensors and serves as the television transmitting station by processing the data for appropriate viewing.

Aircraft with a five-tube EFIS will typically have three Symbol Generators. One will operate the pilot's EADI and EHSI, a second will perform a similar function for the co-pilot's information. The third Symbol Generator provides for the MFD. In the event of a system malfunction, a method of electronic substitution is frequently included. This enhances troubleshooting the system by supplying a second data source to the flight deck displays.

This leads me to believe that "tube" is short for "cathode ray tube".

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  • $\begingroup$ Interesting. How would a Universal Avionics EFI-890R EFIS be classified then? $\endgroup$ – PIXP Aug 23 '18 at 12:16
  • $\begingroup$ @PIXP no idea, that's not my field. sorry $\endgroup$ – Federico Aug 23 '18 at 12:19

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