Updated 4 Dec 2016
S.P. Leitheah, Deputy Director Civil Air Traffic Operations:
The aircraft was 55 nms North of Reus when the crew first sighted the object some 6 nms ahead and to port. It crossed left to right at right angles and then turned and came towards the aircraft, passing below and to the starboard. It was difficult to assess distance because of haze and lack of knowledge of size, but it was estimated to pass within a ¼ to ½ mile.The object remained in sight for a total of approximately 2 ½  minutes and its final heading was due South. The aircraft was flying at a Flight Level 170 heading approximately due North in a clear sky with haze and the sun setting to port. There was no apparent drift and the incident was reported to Barcelona Control on radio telephony and later, on landing, to the RAF Duty Office at Manston. (Copy sent to Ministry of Defence, S(4) (Air).

Richard Hall:
Sept. 10, 1967; Barcelona, Spain
5:35 p.m. GMT (1:35 p.m. EDT). Just before sunset, an airliner crew flying northbound at 16,000 feet watched a metallic, maneuvering cone, with point upward and with mist around its lower portion. The object turned, changed course, descended and approached the airliner, passing under its starboard wing at an estimated 600-700 knots and disappearing to the south after 2-3 minutes. (Hall, 2001, p. 130 from: Volunteer Flight Officer Network, report via United Airlines; McDonald, 1968b, Case #6, reprinted in Vaughan, 1995, pp. 127-28; MUFON UFO Journal, Sept. 1987, p. 19; London Daily Express, 9/11/67 and 9/14/67; U.F.O. Investigator, Vol. IV, No. 3, Nov.-Dec. 1967 p. I.)