Airport Time Zones

Program.cs

using System.Text.RegularExpressions;
using GeoTimeZone;        // Import from Nuget package "GeoTimeZone"  (https://github.com/mattjohnsonpint/GeoTimeZone)
using TimeZoneConverter;  // Import from Nuget package "TimeZoneConverter"  (https://github.com/mattjohnsonpint/TimeZoneConverter)

namespace AirportTimeZones;

internal static class Program
{
    private static void Main()
    {
        // Get the airports.csv data file from here: http://ourairports.com/data/

        using var reader = File.OpenText("airports.csv");
        var header = reader.ReadLine();
        if (header == null)
            return;

        var csvRegex = new Regex("((?<=\")[^\"]*(?=\"(,|$)+)|(?<=,|^)[^,\"]*(?=,|$))", RegexOptions.Compiled);

        var columns = csvRegex.Matches(header).Select((m, i) => new { m.Value, Index = i }).ToDictionary(x => x.Value, x => x.Index);
        var typeIndex = columns["type"];
        var latIndex = columns["latitude_deg"];
        var lonIndex = columns["longitude_deg"];
        var codeIndex = columns["iata_code"];

        var results = new Dictionary<string, string>();
        string[] badCodes = { "", "-", "---", "0" };

        while (reader.ReadLine() is { } line)
        {
            var values = csvRegex.Matches(line);

            var type = values[typeIndex].Value;
            var code = values[codeIndex].Value;

            if (badCodes.Contains(code) || type == "closed" || results.ContainsKey(code))
                continue;

            var lat = double.Parse(values[latIndex].Value);
            var lon = double.Parse(values[lonIndex].Value);
            var tz = TimeZoneLookup.GetTimeZone(lat, lon).Result;

            results.Add(code, tz);
        }

        using var writer = File.CreateText("timezones.csv");
        
        writer.WriteLine("\"iata_code\",\"iana_tz\",\"windows_tz\"");
        foreach (var item in results.OrderBy(x => x.Key))
        {
            if (!TZConvert.TryIanaToWindows(item.Value, out var windowsTimeZone)) 
                windowsTimeZone = string.Empty;
            
            writer.WriteLine("\"{0}\",\"{1}\",\"{2}\"", item.Key, item.Value, windowsTimeZone);
        }
    }
}

timezones.csv

Updated data again with GeoTimeZone 3.2.0 (IANA 2018d)

Updated data again with GeoTimeZone 4.0.0 (IANA 2019a)

@humanyu - That's evident in the data. There are 8812 rows, the first row contains headers, so there are 8811 airport codes in this data set as of the last update. Keep in mind the airport data comes from http://ourairports.com/data/