Total Approaches and autofill of enumerated approaches

In a previous entry, I describe MyFlightbook's model of logging a total approach count and then optionally describing subsets of those approaches.  The idea is to strike a balance between ease of data entry and ease of computation for things like 61.57(c) instrument currency and totals.

So, for example, if you go up and practice a bunch of approaches, you might do 2 VOR approaches and one ILS approach.  In this scenario, you'd log "3" in the "Approaches" field, and then use the "Approaches - VOR" and "Approaches - ILS" properties to log 2 and 1, respectively.  Putting "3" in the approaches field lets the currency computation for instrument currency know unambiguously that you performed 3 approaches; the remaining properties are really just for your convenience if you like to know how many ILS or VOR approaches you've performed.

Expanding on that last point a bit: it's fine if you simply log "3" in the approaches field and don't bother with any of the subset properties (although 61.51(g)(3)(i) does require that you provide the location and type of each approach; this can be done in an unstructured textual manner in the comments for the flight or in the "Approach Name(s)" property).

There are a whole bunch of possible approach types in the system (ILS, VOR, RNAV, NDB, etc. - 43 different kinds at the moment, actually!) and these are flagged as approaches.  

As a convenience, when you save a flight that has one or more of these approach properties, but that has no total approaches indicated, it assumes that you were not explicitly declaring 2 total approaches but rather that you neglected to fill in that field. For that reason, it adds up the enumerated approaches and auto-fills the Approaches field.

So, for example,

Flight has:	Then:
2 ILS approaches 1 VOR approach Empty "Approaches" field	Approaches field is auto-filled to 2 + 1 = 3
2 ILS approaches 1 VOR approach 5 in the "Approaches" field	Flight is unchanged - clearly stated there were 5 approaches, and you've described 3 of them
2 ILS approaches 1 VOR approach 2 in the "Approaches" field	Error - you've described more approaches than the total that you indicated.

A key observation about this is that the math above only works because the properties that are tagged as approaches are mutually exclusive: a given approach cannot simultaneously be an ILS approach and an NDB approach, so adding the two together is OK.

There are a number of approaches that you can describe with properties, though, that are not flagged as being approaches and thus do not result in the autofill behavior described above.

The first of these is "Approaches - Visual," for the obvious reason that you don't want this to count towards your total approaches because it would mess up your 61.57(c) currency (which requires you to flight by reference to instruments).

The other exception to the autofill rule are approaches that are not mutually exclusive with other approaches.  This includes things like Category I/II/III approaches, RNP approaches, or coupled vs. hand-flown approaches.  These are subsets of the subsets, if you will: think of them as an adjective/modifier/constraint on a procedure, as opposed to a particular type of a procedure.

So, for example, if you fly 3 ILS approaches to a runway, 1 of which was a Category II approach and the others were vanilla ILS approaches, you might log 3 ILS Approaches and 1 Category II approach, but it would be a mistake for the auto-fill feature described above to fill in "4" for the total approach count.

For that reason, these "approaches" are not flagged internally as actually being approaches, and thus will not trigger auto-fill of the approaches field; they're really for your recordkeeping benefit only.