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What kind of hardware redundancy is used in integrated modules avionics based architecture for EFIS displays running on a single processor?

My question is specific to redundancy of display hardware driving three different displays. I'm not sure if such kind of thing is implemented before, but I'm trying to run three different displays with a single processor.

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  • $\begingroup$ Do have a question about a specific aircraft or display system? Different systems use different methods to achieve the needed redundancy. As your question is worded is likely to be closed for being unclear or too broad. $\endgroup$ – Gerry Oct 24 '18 at 16:22
  • $\begingroup$ I might be able to answer the question as-is, but are you asking about redundancy in the FMC and FGS hardware driving the display, redundancy between displays, or redundancy in an individual display's hardware? Also, would this be one processor per display? What are you trying to accomplish, and what was missing from your previous questions? $\endgroup$ – Cody P Oct 24 '18 at 16:45
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    $\begingroup$ My question is specific to redundancy of display hardware driving three different displays. I'm not sure if such kind of thing is implemented before, but I'm trying to run three different displays with a single processor. $\endgroup$ – santosh kumar Oct 24 '18 at 16:59
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    $\begingroup$ Why are you trying to run 3 displays from one processor, rather than each display from its own processor? $\endgroup$ – selectstriker2 Oct 24 '18 at 19:46
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Your question is originally asking for "hardware" redundancy, of which there is none. However, there is operating system and software redundancy built to alleviate hardware issues.

Typical computer based avionics like the EFIS must be FAA-compliant with ARINC 653. Of course, in an experimental aircraft, you could potentially get non-compliant avionics, but there's not much of a market for them.

ARINC-653 requires that there be an real time operating system layer implemented as a form of redundancy. This is a special "round-robin" form of operating system, which in layman's terms, means that the operating system will only spend up to a fixed amount of time on a process before hopping to the next one, meaning that a single process hanging will not halt the rest of the partitions. You might have a navigation process that dies, but the GPS process can continue to operate as it is in a separate partition. It also has partial requirements that partitions are not dependent on each other, but instead retrieve their data directly from sensors. This gives another layer of redundancy in case a dependency crashes.

ARINC 653

Running three displays off one processor is ill-advised, and would never be FAA-compliant, but it is technically possible. You would however have to heavily modify the operating system, and the "Guest OS" (ARINC 653) layer.

I'm happy to go far more indepth into this on StackOverflow if you choose to ask a follow up answer there, but the technical specifications are a bit out of scope for the Aviation StackExchange.

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Broadly speaking the redundancy comes in the fact that there are multiple displays that can usually serve all the functions of the EFIS. Most typical electronic instrumentation installations have at least two screens both of which can typically show primary instrumentation (PFD).

Even some of the smallest drop in options these days are capable of serving as both AI/speed/altitude instruments as well as HSI units so if a pair of two is installed you have redundancy for you primary instrument displays.

Larger airliners like the 737 have multiple displays that can be configured in almost any combination in the event of a failure and seem to be driven by two computers.

The NG's have 6 Display Units (DU's), these display the flight instruments; navigation, engine and some system displays. They are controlled by 2 computers - Display Electronics Units (DEU's). Normally DEU 1 controls the Captains and the Upper DU's whilst DEU 2 controls the F/O's and the lower DU's. The whole system together is known as the Common Display System (CDS).

The DU's normally display the PFD's outboard, ND's inboard, engine primary display centre (upper) and engine secondary display lower. Although they can be switched around into almost any other configuration with the DU selector (shown left).

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