Sunday, January 10, 2021

Models - In Depth and Best Practices

Aircraft and models on MyFlightbook are crowd-sourced and shared amongst its users.  This has a huge benefit for the comprehensiveness of the data and - with a bit of curation - with the accuracy of the data as well.  The ability for any registered user on the system to make changes here is a powerful tool.  Any powerful tool, however, carries risk if used incorrectly.  In this post, I'll talk about how the models part of system works, how it is properly used, and how the risk is managed.  (Spoiler alert: in practice, the system works well and so the risk is negligible.)

The difference between an aircraft and a model on MyFlightbook

The important thing to understand on MyFlightbook is that a "model" encapsulates a set of attributes that are common across a set of multiple airframes.  This includes attributes like the category/class of the aircraft, whether it is turbine or piston, high-performance, has retractable gear, and so forth. For more detailed information, please read my previous post.
So, for example, there is one "Cessna C-172 R" in the system, but there are (as of this writing) nearly 1,600 distinct aircraft in the system that are tied to the "Cessna C-172 R" model.  It is the "Cessna C-172 R" model that captures the fact that it is an airplane, single-engine/land ("ASEL"), piston, not high-performance, not tailwheel, ICAO code "C172", marketing name "Skyhawk", and so forth.

Data points that vary from airframe-to-airframe are stored on that aircraft's record in the database.  The tail number (registration) is the most obvious such piece of data, but there are private notes (notes only you can see), shared notes (visible to anyone who flies that aircraft), maintenance records, glass/TAA upgrades, and other data.

It's worth briefly pointing out two special cases within this model.  The first is that not all aircraft in the system are flying machines - some are training devices/sims.  While there are some special rules around these, you use them in your account the same way you would use any other aircraft, it's just that instead of being a flying machine it's an ATD or an FTD or an FFS.  In fact, some models of aircraft (such as anything created by Frasca or Redbird) are flagged as "Sim only", so the system knows not to let you create registered aircraft with that model.  See here for more information about simulators/training devices.

The other special case is that of an "anonymous" aircraft.  An anonymous aircraft is just like any other aircraft, except that it has no specific tail number.  Internally, it has a pseudo-tailnumber that is the hash mark (#) followed by a series of digits that represent the model.  For example, the anonymous C-172R is "#000099". That tail number is used for unambiguous identification of an aircraft when importing/exporting, but in general the system will show the underlying model name ("Anonymous C-172R") rather than the #000099 tail number.  Because that's a single number for an anonymous instance of a given model, anonymous aircraft are necessarily shared amongst pilots.

Relationship between Aircraft and Models

A key attribute of how shared aircraft/models work is to understand that these relationships are all computed in real-time.  That is, an aircraft in the database does not have any information about its associated model, it only has a reference to the model.  In turn, the model holds a reference to the manufacturer and even to the category/class.

So when you see "N12345 - Cessna C-172 (ASEL)" in your account, that is all being assembled in real time: I look up "N12345" in the database and find the ID of a model.  I then look up that model and find that it has model name of "C-172", an ID of a manufacturer and an ID of a category/class.  I then look up the manufacturer that has that ID and find that the manufacturer is named "Cessna" and I look up the category/class by its ID and discover that it is "ASEL".  

Because none of this data is stored directly in the aircraft, all changes happen immediately to all related aircraft.  For example, if you were to edit the C-172 model to be a helicopter rather than ASEL, then instantly not only would N12345 become a helicopter, but ALL aircraft in the system that are linked to that model would also become helicopters.  Any subsequent totals computation or currency computation involving any aircraft tied to that model would suddenly now have helicopter time and helicopter currency.

That can be risky, but in practice it works just fine.  First and foremost, there's an honor system involved that people don't make random edits like changing a C-172 to be helicopter.  For 14 years and counting, this has worked extraordinarily well.  But as a backup ANY edit to a model results in an email being sent to the site admins, which details the specific change, and that can be reviewed and modified (or reversed) by the admin.  As it turns out, the vast majority of edits to models are minor things like indicating high-performance, or editing the name to be consistent with other similar models.

Admins also review any newly created models in the system for errors, consistency, and redundancy; if a new model is redundant with another existing model, then the two will typically be coalesced.  No notification is generated when that occurs.

Editing aircraft works in the same way, but obviously the scope of the impact is limited to pilots in that specific aircraft, and there are a few other rules involved (see this post about aircraft edits).  In this case, email about the changes is sent not only to the admins for review, but to other pilots who fly that aircraft as well.  This ensures that all changes are reviewed, and that errors are quickly caught and fixed.

Best Practices and Conventions

Please try to follow these guidelines when editing models:

  • If a specific aircraft is wrong (e.g., is the wrong model), then edit the aircraft, not the model.
  • Only edit a model if the definition of the model itself is wrong and thus if all aircraft associated with that model need to be corrected.  E.g., if you see a Boeing 737 listed as piston, then you should edit it.
  • Please do a search for existing models before creating or editing a model; there's a good chance that the model you want is already in the system.  When you create a model, the system will also check to see if it looks like you're creating a duplicate and will show you existing models that look like matches.  While it's best to re-use an existing model, you can proceed if it truly isn't a match.
  • The FAA (and other authorities) have a particular level of granularity for models; ICAO uses another.  Since MyFlightbook launched in 2006, it's been pretty clear that the community prefers more granularity/precision to less.  So you'll see many model designations on MyFlightbook that might map to the same designation within these registries.  That's OK and a good thing.  There's no problem with having more fine-grained distinctions based on upgrade packages, aircraft vintage (e.g., when one manufacturer gets sold to another), and so forth.  As a simple example, there are enough G1000-equipped C-172S’s out there that it’s got its own model designation in the system, even though it’s simply a C-172S.
  • Glass and TAA are one area where things are often confused, since these can be part of the base design (All Boeing 787's that have ever been made are glass/TAA), a factory option (even if everybody orders glass as a practical matter), or an upgrade to a specific airframe.  In general, the model should indicate glass/TAA only if it is part of the base design.  If it's a factory option, it should either be indicated on the airframe, or alternatively it's OK to create a new model that is explicitly a glass-only variant.  For example, there are so many G-1000 equipped C-172S's that there is both a "C-172S" in the system that is not marked as glass (so you'd indicate glass on the specific airframe if it is glass), but there is also a "C-172S G-1000" model in the system that is all glass.

An admin will review EVERY new model and EVERY edit to a model in order to check for redundancy and consistency.  Generally, this requires some triangulation between multiple sources.  Not only that, but I often have more granularity than any one of the sources. If two variations look identical, I’ll merge them, but otherwise I will allow it.  I do, however, try to enforce some consistency.

Here are some of the conventions I try to follow.  Some are a bit more ambiguous than others.

The “Model” field is probably the least well defined.  I tend to use a combination of:
  • The FAA registry page or comparable non-US websites.  Note that this is not always super precise (sometimes listing a C-150 as a “150” instead of, say, a “C-150M”) and if registrations have been reassigned the old one assignment might not be present.  But it will generally distinguish, say, a C-172S from a C-172P.
  • Wikipedia
  • MyFlightbook user community.  In particular, this helps with 4 specific conventions:
    • Hyphenation conventions.
    • Distinguishing float vs. wheel versions of an aircraft: generally you would name a C-172 on floats “C-172 (Float)” to highlight the distinction from its wheeled counterpart. (See here for more on floats/amphibs).
    • Distinguishing sim-only versions of an aircraft.  E.g., a Flight Safety 737 would typically be “B-737 (SIM)” so that nobody thinks they can create a real flying 737 using that model.
    • Where models can have conversions that make them high-performance or give them a constant-speed prop, we’ll generally add “(FP)” for “Fixed Prop”, “(CSP)” for “Constant Speed Prop” or “(HP)” for “High Performance next to the model name.  E.g., “C-172 M/180HP (CSP)” for the superhawk variant of the 172 M that has a constant speed prop and a 180HP engine.
Note that because of the desire for high-precision, sometimes the model in MyFlightbook will deviate from the "nameplate" model.  An example here is the PA24.  Piper made multiple PA24 models; the plain "PA-24" had a 180hp engine, while subsequent variants with more powerful engines included the horsepower after the model - e.g., "PA-24-250" with a 250hp engine, or the "PA-24-260" with a 260hp engine, and so forth.  But the 180hp engine was simply "PA-24" on the nameplate; there technically was never a "PA-24-180".  On MyFlightbook, though, there is both a "PA-24" and a "PA-24-180".  This is because the former could mean "It was a PA-24 with 180hp", or it could mean "It was a Piper PA-24, but I don't remember which variant it was."  So the latter allows you to very clearly indicate the 180hp meaning.

The ICAO designation field is much more precise, and we treat the ICAO website as an authoritative source. Note that this really only applies for Airplanes and Helicopters on MyFlightbook.  ICAO tends to lump all balloons into "BALL" and gliders into "GLID", but that's a coarser granularity than the community generally want, so please leave the ICAO field blank for anything that is not an airplane or helicopter.  

Also note that the ICAO code is very coarse: multiple different variants of an aircraft often share a single ICAO code; the C-172 is a great example: all C-172’s are “C172”, whether it’s a C-172P, C-172N, C-172RG, etc. 

For the Type Rating field (generally only jets or large aircraft), MyFlightbook treats the FAA Type ratings taxonomy as authoritative.  It isn’t totally comprehensive, but I use it when possible.

Summary - don't sweat it!

There's a lot to digest above, but the key thing to remember is that someone will review any (a) new model, (b) edit to an existing model, or (c) edit to an aircraft that has the potential to impact other pilots.  So do your best, but don't worry about getting everything just right; we've got your back.  

At the end of the day, this results in a super comprehensive and increasingly accurate data set, which benefits us all.

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