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?


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.


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".

  • $\begingroup$ 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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