I am no expert at the Development Assurance Process, but hypothetically speaking what Design Assurance Level (DAL) would a human pilot receive if they were classified as one (i.e. DAL A, B, C, D, E). It seems absurd to try and answer this question since the plane can't even leave the gate today without a pilot or pilots, but I am hoping to learn more about the DAL process thru any answers received.

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    $\begingroup$ "It seems absurd to try and answer this question..." I agree. $\endgroup$ Aug 20, 2019 at 0:35
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    $\begingroup$ Come on, at least tell us what DAL means. $\endgroup$ Aug 20, 2019 at 1:16
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    $\begingroup$ @quietflyer see the DO-178 specification for definition of DAL (or quick summary here en.wikipedia.org/wiki/DO-178C) $\endgroup$
    – Daniel K
    Aug 20, 2019 at 2:31

1 Answer 1


I'm oversimplifying a bit, but more or less the DAL level of a piece of software is decided by asking the question, "What is the worst that could happen if this software fails to operate as designed?" Note that "failure" in this case could mean that it simply stops working, but it could also mean that it does the wrong thing, like pitch up when it should pitch down. So for example,

  • The software that runs the in flight entertainment system. Worst thing that could happen has no safety effect whatsoever, therefore level E.
  • The software that runs certain cockpit indicators, like the engine vibration display or engine oil temperature display: Usually considered a "major" safety effect, but not more than that, so level C.
  • The software that controls the engine thrust: if that fails to set the thrust according to the pilot demand, that could result in the plane crashing, so "catastrophic effect", thus level A.

It may be a little subjective, but I'd say that if we consider the pilot to be "software", if the pilot fails, the worst thing that could happen would be "Catastrophic" condition, and thus I would label the pilot as level A software.

Edits: clarified that DO178 applies specifically to software

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    $\begingroup$ "In flight entertainment system. Worst thing that could happen" - Swissair 111? $\endgroup$
    – Zeus
    Aug 20, 2019 at 7:43
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    $\begingroup$ @Zeus Swissair 111 was a wiring problem. In that particular case, that wiring happened to be for the IFE system, but the exact same problem could in principle have developed with any other wired system. Therefore, if anything, it stands to reason that you should apply the same reasoning at least to any wiring carrying significant voltage or power. $\endgroup$
    – user
    Aug 20, 2019 at 11:12
  • $\begingroup$ @Zeus interesting, I was unaware of that one. In any case, DO-178C only applies to software. There are separate regulations governing hardware. i.e. flammability and electric wiring don't fall under DO-178C. I'll edit the answer to be more clear on that. $\endgroup$
    – Daniel K
    Aug 20, 2019 at 12:17
  • $\begingroup$ @aCVn, true, of course, but it shows that it's dangerous to think (and state unconditionally) in that vein. The system has to be considered as a whole. We can even speculate what could happen from a software bug, assuming correct wiring: say, an infinite loop causing excessive power consumption for all seats at once -> failure of circuit breaker -> shedding of more critical load. $\endgroup$
    – Zeus
    Aug 21, 2019 at 0:42

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