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Does the FAA have any regulations governing the design of a turbine engine FCU? I'm being questioned about an older Beechcraft PT6A FCU - in particular, how can I guarantee that when the power condition lever is at the shutoff/cutoff position, no fuel is moving to the combustor...? Any help would be appreciated... Thanks!

Edit - for those needing clarification:

Does the FAA have any regulations governing the design of a turbine engine FCU?

Simply as stated, does the FAA regulate how a turbine engine FCU can be designed - pressure allowances, flow volumes, etc.

I'm being questioned about an older Beechcraft PT6A FCU - in particular, how can I guarantee that when the power condition lever is at the shutoff/cutoff position, no fuel is moving to the combustor...?

As stated, I'm being asked to prove that when the power condition lever in the cockpit is moved to the shutoff/cutoff (pick one term) position, fuel will not flow into the combustor. Tying into my first question, does the FAA regulate that a turbine FCU MUST absolutely cut off all fuel moving to the combustor, or is that just left to the designer to ensure...?

Hope that clarifies everything. Not sure how much more detailed I can get without specific and possibly pointed questions.

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  • $\begingroup$ Thanks @RalphJ, the question was answered below. But I appreciate the effort! $\endgroup$ – Jedi Engineer Feb 28 '18 at 11:46
  • $\begingroup$ @JediEngineer Yes the question is answered, but it is still unclear and about to get closed. Please rephrase it so that it can be a valuable question. $\endgroup$ – Farhan♦ Feb 28 '18 at 15:22
  • $\begingroup$ @fooot. Can I please ask why this question is on hold? It might be unclear to you what they were asking, but it was crystal clear to me. My answer has been accepted, so my understanding must be correct. So, logically, then the decision to put it on hold because "it's unclear" is wrong. Can you please remove the hold on this question. Maybe the answer was accepted after you put the question on hold (if that is actually possible). Alternatively, can it be explained why a question that has an accepted answer, and therefore must be an appropriate and correct answer, is "unclear"? Thank you. $\endgroup$ – Penguin Mar 1 '18 at 12:33
  • $\begingroup$ @Penguin The answer was accepted before it was put on hold. And fooot alone did not put it on hold, several people think that. Since the question is crystal clear to you, can you please make it clearer for those who did not understand it and then it will be submitted to be reopened. $\endgroup$ – Farhan♦ Mar 1 '18 at 14:18
  • $\begingroup$ @foot, I'm not entirely sure how much more I can clarify this question but I'll try. But it's pretty straight forward if you read it sentence by sentence. $\endgroup$ – Jedi Engineer Mar 1 '18 at 18:50
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Subpart E (Powerplant) of Part 23 (AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND COMMUTER CATEGORY AIRPLANES) has quite a few regulations regarding fuel system operation. In particular, section 23.995, "Fuel Flow".

However, I could not see in there a regulation requiring no fuel to flow in the off position, but given the safety implications of that not occurring, I would fully expect that is a requirement that needs to be demonstrated.

It appears to exist in Part 33 (AIRWORTHINESS STANDARDS: AIRCRAFT ENGINES), subpart E (Design and Construction; Turbine Aircraft Engines) section 33.75 "Safety Analysis". This states:

The applicant must analyze the engine, including the control system, to assess the likely consequences of all failures that can reasonably be expected to occur.... The safety analysis must also include, but not be limited to, investigation of the following: (vii) complete inability to shutdown the engine.

I don't expect there are any regulations defining how it needs to be designed to do this - but rather regulations saying what it needs to do, and the way of achieving it is left up to the designer.

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  • $\begingroup$ thank you so much! This leaves a little to interpretation, but it has solved my issue. Thanks again! $\endgroup$ – Jedi Engineer Feb 28 '18 at 11:28
  • $\begingroup$ I was able to further trace that regulation back to the year the PT6 was first created, to further find that the FAA didn't exist back then, and aircraft were under a 3 page regulation from the CAA, which grandfathers in under the FAA regulations. Turns out that the FAA doesn't say a turbine FCU must cut off the fuel when placed in that position, but it is considered a hazard if it doesn't. $\endgroup$ – Jedi Engineer Mar 1 '18 at 19:02
  • $\begingroup$ @JediEngineer. Interesting, but quite believable since the PT6 is kind of the engine version of grandfathers axe! It's been around for a long time, and possibly every part has been changed and improved, except for the name...! $\endgroup$ – Penguin Mar 2 '18 at 9:44

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