Take-off airfield

The rule behind Take-off place and time zone. The time zone half is in Flight analysis §8.2.

Reference implementation: vulture-ios/Packages/Airports/Sources/Airports/AirportManager.swift (airport(for coordinate:)) and vulture-ios/Packages/Persistence/Sources/Persistence/Extensions/CoreData/CoreFlight+CoreData.swift (processTakeoff(with:)).

The airports table

vulture-ios/Packages/Airports/Sources/Airports/Resources/airports.json: 47,991 airfields, 4.6 MB (1.3 MB gzipped). Built by vulture-ios/Scripts/prepare_airports.rb from the OurAirports CSVs (public domain): only small_airport, medium_airport and large_airport, with their radio frequencies.

One JSON array of objects with one-letter keys:

Key	Field	Type	Example
a	name: the OurAirports municipality, or the airfield name when there is none	string	"Genk"
b	latitude	number	51.0154
c	longitude	number	5.52647
d	country, ISO 3166-1 alpha-2 (iso_country)	string	"BE"
e	code: the OurAirports ident (the ICAO code where one exists; unique in the file)	string	"EBZW"
f	frequencies, optional	[{ "s": description, "r": MHz }]	[{"s":"Genk radio","r":"120.4"}]
g	elevation in feet, optional	string	"278"

So a flight from Zwartberg (EBZW) reads “Genk 🇧🇪”: the town, not the airfield’s own name.

Every platform ships this file, byte for byte, so the same flight gets the same airfield everywhere. To refresh it, run the script in vulture-ios and copy the result.

Lookup

airport(for: coordinate):

1. No coordinate → no airfield.
2. Take the airfield with the smallest distance to the coordinate. The distance is the Map package’s CLLocationCoordinate2D.distance(from:) (vulture-ios/Packages/Map/Sources/Map/Helpers/CLLocationCoordinate2D+Calculations.swift): a haversine on a sphere of radius 6,371 km, not CLLocation.distance. Android uses its port, core.geo.distance. (The time zone lookup is the other way round: it measures with CLLocation.) On a tie, the first one in file order wins (iOS sorts with Swift’s stable sort).
3. If that airfield is more than 3,000 m away, there is no airfield. Out-landing fields and hill sites usually end up here.

The result fills three fields on the flight:

Flight field	From
takeoffCode	e
takeoffName	a
takeoffCountryCode	d

When it runs

• Once per flight, when the flight is first saved to the logbook. The coordinate is the analysed take-off fix (Flight.takeoffFix, the first fix with the TAKEOFF event).
• isTakeoffProcessed is then set to true, also when no airfield was found or the flight has no take-off fix. A processed flight is never looked up again, so a pilot’s edit or a sync from another device is never overwritten.
• The fields and the flag are part of the flight’s sync record (sync schema).

Where it is used

Use	Rule
Flight detail	The code in the info tab; the location is takeoffName and the flag of takeoffCountryCode, joined by a space (iOS CoreFlight.takeoffLocation).
Logbook search	Matches takeoffCode and takeoffName.
Logbook countries filter	One entry per distinct takeoffCountryCode of the logbook’s flights. A country is matched without regard to case. The section is hidden when there are none.
Charron scoreboard	The start ICAO code is looked up by code (airport(for icao:), the first exact match); ZZZZ and unknown codes stay as sent.