Wednesday, 1 January 2014

iNavCalc Data Sources

Updated 19 February 2015 to include openAIP.net source

Here is the current list of sources where iNavCalc gets its data. You will note that some sources are official, but since FlyLogical is not an official (re-)distributer of such data, all FlyLogical web-pages and apps carry a warning and disclaimer about not relying on the data without reverting to the original official sources.


  • METARs and TAFs:   US National Center for Atmospheric Research (NCAR) under sponsorship of the Federal Aviation Administration (FAA). This is an official data source. URL:  http://weather.aero 
  • NOTAMs: US FAA Aeronautical Information Data Access Portal (AIDAP). This is an official data source.
  • Atmospheric temperatures and pressures used in PLOG calculations: same source as METARs for surface data, then application of standard atmosphere model to extrapolate from surface measurements to flight altitudes. For each waypoint, data from the nearest METAR reporting station is used, so results must be considered as approximate.
  • Winds-aloft used in PLOG calculations: same source as METARs for surface data, then application of boundary layer model to extrapolate from surface measurements to flight altitudes (see http://es.ucsc.edu/~jnoble/wind/extrap/index.html ). For each waypoint, data from the nearest METAR reporting station is used, so results must be considered as approximate. Note: previous versions of iNavCalc utilised the NWX web-service ( http://www.navlost.eu/aero/nwx_help ) for deriving winds-aloft forecasts from the NOAA GFS models ( http://www.ncdc.noaa.gov/data-access/model-data/model-datasets/global-forcast-system-gfs ). However the NWX service has been intermittent of late, and no longer seems to be actively supported. As such, the alternate method of extrapolating from METAR surface winds has been adopted. This approach must be understood to be approximate,  not least since the boundary layer model is itself approximate. Moreover, an average value of 0.1 is assumed for the surface friction parameter in the model, thereby not taking account of local variations.
  • Geomagnetic declination: a local implementation of the World Magnetic Model (WMM), developed jointly by the National Geophysical Data Center (NGDC, Boulder CO, USA) and the British Geological Survey (BGS, Edinburgh, Scotland) . URL: http://www.ngdc.noaa.gov/geomag/WMM/DoDWMM.shtml
  • Solar angle calculations: local model based on Earth-Sun orbital model
  • Airport database: originally derived from the OurAirports.com community-maintained database, complemented thereafter by FlyLogical and by iNavCalc users
  • NAVAIDs database: originally derived from the OurAirports.com community-maintained database, complemented thereafter by  FlyLogical and by iNavCalc users
  • NAVCOM frequencies: originally derived from the OurAirports.com community-maintained database, complemented thereafter by FlyLogical and by iNavCalc users, and since 19 February 2015, automatically updated via openAIP.net on a weekly basis