The Trident was a revolutionary three-engined 'Tri-liner' which incorporated many advanced design features, not least of which was a fully automated instrument landing system, an incredible innovation which is now standard on many of the world's jetliners. Allowing the aircraft to effectively perform blind landings in zero visibility conditions, the first commercial fully automatic landing was performed by a Trident flying from Paris to Heathrow on 10th June 1965, another significant first for the British Aviation industry. With the Boeing 727 attracting all the sales the originally configured Trident might have hoped to secure, only 117 were eventually built in four major variants, with the largest operator British Airways retiring their aircraft in 1985.