The Spanish Air Force’s Alcorcón dossier preserves six photographs submitted in 1978 and a computer-assisted analysis written sixteen years later. The pictures show bright traces above an urban skyline. The analyst interpreted two as aircraft-related and suspected manipulation in four others, but the original first-generation negatives were unavailable.
That distinction determines the outcome: Possibly Explained. The file contains specific proposed causes and an explicit fraud suspicion; it does not contain a demonstrated reconstruction using the original negatives or a confession establishing how the entire photographic set was made. Its value lies in the surviving images and the reasoning, limits and chronology of the later review.
How the photographs reached the military
A covering note dated 7 June 1978 forwarded photographs to the Military Secretariat. It said the person who supplied them claimed to have taken them from an upper-floor apartment in Parque de Lisboa, Alcorcón, looking towards the Andalusia road. The note referred to conditions written on the backs of the photographs.
Parque de Lisboa is the neighbourhood named in the record; the account does not describe an observation made inside a public park. The private apartment’s floor or address adds no useful public-access information and is not needed to map the broad reporting area.
The file’s cover and later release summary assign the case to 19 March 1978. That is the incident date used here. The June letter concerns submission, the 1994 date concerns analysis, and the 1995 paperwork concerns release. They should not be conflated into a single continuous period of encounters.
What was missing from the original inquiry
The later summary explicitly says that no investigating officer had been appointed and no statement had been taken from the photographer to clarify the conditions. That is a substantial limitation. A military office receiving prints is different from a contemporary inquiry establishing the camera, exposure settings, sequence and what the photographer actually saw.
The surviving ten-page release reproduces the photographic material on three pages. The backs referred to in the covering note are not reproduced as a complete set of readable technical descriptions. It is therefore inappropriate to fill the gaps with an invented exposure duration, a precise camera model or a detailed eyewitness narrative.
Much later, the operational air command requested an analysis to attach to the file. The resulting four-page note, dated at Seville on 20 June 1994, is the source of the aircraft and manipulation interpretations. Those are later assessments of submitted material, rather than findings of a 1978 on-site investigation.
The computer work described
The note explains that the initial work involved enlarging details, altering grey tones and adjusting brightness and contrast. It then describes assigning colours to different grey values so that boundaries and tonal differences would be easier to distinguish.
It names Picture Publisher 3.0, Corel Photo-Paint 3.0 and Photo Styler 1.0. The description of changing palettes in a 256-colour PCX workflow is useful because it says what the processing actually did. Colours in these processed versions were assigned to tonal values; they were not colours recorded by a temperature-sensing camera.
The analyst calls one transformation an approximate form of thermography. That wording must be read alongside the stated procedure. Recolouring a greyscale image does not supply an independently recorded thermal measurement of a target. The file does not establish temperatures, hot propulsion equipment or a heat signature for an unfamiliar vehicle.
The first photograph
The analyst interpreted photograph 1 as a trail left by a jet aircraft. In that reading, the aircraft itself was outside the frame and the photograph captured the trail. The suggested direction was from the right of the photograph towards the left.
This is a concrete ordinary-aircraft explanation for one image. It is not a radar identification, a matched flight record or a recovered original negative proving the exposure’s circumstances. The distinction is worth retaining even when an interpretation appears plausible.
The note also discusses conspicuous grain and suggests high-sensitivity film, probably Kodak Tri-X at 400 ASA, perhaps pushed to 1,000 during processing. These are the analyst’s inferences from the material examined, not camera or laboratory records supplied by the photographer.
The four images suspected of manipulation
For photographs 2–5, the analyst said the processing revealed no solid object at either end of the traces or along them. Some portions of the luminous streaks were brighter than others. The note offered two ways in which such marks might have been made during photographic production.
One suggestion was moving a concentrated point of light across sensitised paper while enlarging a negative. The other was scratching the negative before printing. The analyst preferred the scratching hypothesis. The report also remarked that the phenomena appeared over the same area and considered either a telephoto lens or later enlargement and cropping.
Those proposals concern the production of particular photographs. They do not demonstrate that somebody performed either operation on these negatives. No experiment reconstructing the marks with the original materials is included in the released record. The strength of the analyst’s suspicion should not obscure that evidential gap.
The conclusion cites areas where the bright trace appeared to have removed the visibility of the photographic emulsion’s grain, leaving the paper texture. That is part of the reasoning advanced for manipulation. It remains an interpretation of the examined copies, with the need for original negatives explicitly acknowledged.
The sixth photograph
The analyst treated photograph 6 differently. Two stationary lights in the wider scene were described as overexposed, supporting an exposure-based interpretation of the luminous marks. The trail was then attributed to an aircraft approaching or departing a landing area.
This differs from the proposed manipulation of photographs 2–5 and the jet-trail interpretation of photograph 1. A responsible account needs all three parts of the assessment. Calling the entire set one proven hoax would erase the analyst’s own separation between ordinary aircraft photography and suspected alteration.
Nor does the existence of bright streaks automatically establish the movement of a solid unknown craft along every visible line. The very question under review was whether those lines represented an external object, exposure effects or marks introduced in photographic production.
The decisive qualification
At the end of the note, the analyst says further enlargement and detailed work were impossible without original first-generation negatives. The writer expected such material, if obtained, to expose fraud more completely. That expectation is not evidence that the negatives were subsequently obtained or tested.
The report also dismisses an atmospheric-inversion possibility using broad statements about where such effects occur. The released file supplies no site-specific atmospheric reconstruction supporting that exclusion. It is retained here as part of the analyst’s argument, without treating it as a demonstrated finding about the night in question.
The later release reviewer found no reason to keep the dossier classified. Declassification does not strengthen the absent photographic chain of evidence, verify the original witnessing conditions or independently validate every claim in the 1994 analysis.
Place and primary record
Approximate map area: 40.35, −3.82, rounded from the GeoNames Alcorcón locality record. The pin marks the reporting town, not a private apartment, a camera position or a position for anything depicted in the photographs. No residential access or public viewing venue is claimed.
Read Biblioteca Virtual de Defensa, dossier 780319 and the ten-page digital release. Physical page 2 summarises the missing original inquiry; page 3 is the submission note; pages 4–6 reproduce the photographic set; and pages 7–10 contain the computer-analysis note and its qualification about negatives.
The lead image reproduces the analysis conclusion under the archive’s explicit CC BY 4.0 digital-copy licence. It is a source document rather than an image presented as verified evidence of a craft. The GeoNames locality record supplies the map reference. Sources, photographic-page reproduction and rights were checked on 13 November 2026.