Editing Boeing 707 (section)

===707-420===
[[File:BEA Airtours 707-400 (cropped).jpg|thumb|A [[British Airtours|BEA Airtours]] -420, powered by [[Rolls-Royce Conway]] low-bypass turbofans]]

The 707-420 was identical to the -320, but fitted with Rolls-Royce Conway 508 (RCo.12) turbofans (or by-pass turbojets as Rolls-Royce called them) of {{cvt|18,000|lbf|kN}} thrust each.<ref>{{cite web |url=http://www.flightglobal.com/pdfarchive/view/1961/1961%20-%201700.html |title= Commercial aircraft - sq ft - ias - 1961 - 1700 - Flight Archive |work=FlightGlobal |access-date=April 1, 2015}}</ref> The first announced customer was [[Lufthansa]]. [[BOAC]]'s controversial order was announced six months later, but the British carrier got the first service-ready aircraft off the production line. The British [[Air Registration Board]] refused to give the aircraft a certificate of airworthiness, citing insufficient yaw control, excessive rudder forces, and the ability to over-rotate on takeoff, stalling the wing on the ground (a fault of the de Havilland Comet 1). Boeing responded by adding {{convert|40|in|cm|abbr=on}} to the vertical stabilizer, applying full instead of partial rudder boost, and fitting an underfin to prevent over-rotation. These modifications except to the fin under the tail became standard on all 707 variants and were retrofitted to all earlier 707s. The 37 -420s were delivered to BOAC, Lufthansa, [[Air-India]], [[El Al]], and [[Varig]] through November 1963; Lufthansa was the first to carry passengers, in March 1960.