transport.rest
Community maintained, developer-friendly public transport API
Flight status, airports, airlines, airline safety and in-flight Wi-Fi data.
Travel Risk Aviation API is a free Transportation API that requires apiKey authentication, is served over HTTPS and supports CORS, so it can be called from the browser.
Details from api.travelriskapi.com.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Community maintained, developer-friendly public transport API
Washington Metro transport API
The Travel Risk Aviation API is provided by Travel Risk API (api.travelriskapi.com).
Yes. The Travel Risk Aviation API is listed in the Transportation category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Travel Risk Aviation API uses apiKey authentication, so you need to register for credentials before making requests.
Yes. The Travel Risk Aviation API supports CORS, so front-end JavaScript can call it directly.
Yes. The Travel Risk Aviation API is served over HTTPS, so it's safe to use in production.