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Can anyone explain what is the difference between a functional check and an operational check in aviation? Basically I faced a problem to prepare the task card for functional and operational check of a FDR (Flight Data Recorder).

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    $\begingroup$ I've only ever done aircraft maintenance in the UK military. I have no idea if this will help or hinder. Functional testing was conducted before flight after maintenance. It answered the question "does the component basic functionality work?" This might include BITE (automated tests, "Built In Test Equipment) and testing with dedicated test equipment. A given component might also need an operational check which was an item added to the next flight plan to confirm the component in airborne use or operated with all other related systems together. $\endgroup$ – Simon Dec 5 '16 at 19:43
  • $\begingroup$ In other words, a functional test only verified the component. An operational test confirmed it's working within the overall system. An example would be a GPS receiver. Functional test - does it lock on, acquire and display a good location fix. Operational test - does it successfully and accurately feed the FMS for flight progress calculations? $\endgroup$ – Simon Dec 5 '16 at 19:47
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From the ATA spec 100 which is the standard for aircraft maintenance documentation, they provide the following definitions:

(c) Following are definitions of three categories of test that shall apply:

1 Operational Test

a. That procedure required to ascertain only that a system or unit is operable. These tests should require no special equipment or facilities other than that installed on the aircraft and should be comparable to the tests performed by the flight crews. It is not intended that the operational test of the unit shall meet the specifications and tolerances ordinarily established for overhaul, or major maintenance periods.

2 Functional Test

a. That procedure required to ascertain that a system or unit is functioning in all aspects in accordance with minimum acceptable system or unit design specifications. These tests may require supplemental ground support equipment and should be more specific and detailed than an operational test. It should contain all necessary information to perform proficiency tests to maintain system or unit reliability at an acceptable level, without reference to additional documents.

3 System Test

a. That procedure containing all adjustment specifications and tolerances required to maintain system and/or unit performance at maximum efficiency and design specifications. It shall be self-contained and may duplicate other tests. It is normally used at major maintenance periods.

I would expect that these definitions are pretty universal in aviation.

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