Real-time Flight Status & Global Aviation Data API.
apilayer aviationstack API is a free Transportation API that requires OAuth authentication, is served over HTTPS and has unconfirmed CORS support.
Access real-time flight data, historical flight information, and tracking with AviationStack API. Get accurate aviation data for efficient flight tracking.
Details from aviationstack.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.
Geospatial data for Mexico City public transport system (Metro, Metrobús, Cablebús, RTP, etc.)
Screen any ship by IMO for OFAC/EU/UN/UK sanctions, ownership opacity and a vetting grade
Predictive port congestion, ETA delay and freight volatility signals for 16 global ports
164,068 aircraft accident narratives from 128 official investigation authorities, plus FAA data
The apilayer aviationstack API is provided by Aviationstack: Real-Time Flight Tracker API (aviationstack.com). Access real-time flight data, historical flight information, and tracking with AviationStack API. Get accurate aviation data for efficient flight tracking.
Yes. The apilayer aviationstack 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 apilayer aviationstack API uses OAuth authentication, so you need to register for credentials before making requests.
CORS support for the apilayer aviationstack API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The apilayer aviationstack API is served over HTTPS, so it's safe to use in production.