Chile.Southern Patagonian Ice Field · the light that crossed ahead of an A321 bound for Punta Arenas

On 17 December 2019, the head of the Air Traffic Services Office at Presidente Carlos Ibáñez del Campo airport in Punta Arenas sent the DGAC's anomalous aerial phenomena committee, then called CEFAA, a report on something the pilots of an airliner had seen in the early hours of that same day, together with an audio file of the exchange in which the pilot asked about other traffic and reported the sighting. According to that first report, at 1:35 local time (4:35 GMT), flight LAN 081, an Airbus A321 from Santiago to Punta Arenas flying south on a heading of about 120 degrees, asked whether there was any traffic nearby and was told there was none. The aircraft was then 8 nautical miles (14.8 km) east of BODOM, a reporting point the report places at 50°21'59" South and 73°46'02" West, over the Southern Patagonian Ice Field, some 350 kilometres north-west of Punta Arenas.

The captain then described an object giving off intermittent flashes. He first saw it 'at 1 o'clock' from his position, which the report renders as about 200 degrees; then 'at 12 o'clock', after which the object crossed his field of view until it disappeared to the east, over Argentine territory. The committee wrote to ask him to fill in a sighting form, and the captain, surnamed Curbelo, sent it on Friday 24 January 2020, five weeks later.

The form does not quite match the control report, and the report says so. The captain places the sighting at 1:55 local time, not 1:35; 40 nautical miles (74 km) north of BODOM, not 14.8 km east; and at 33,000 feet (10,050 metres), not 31,000 (9,450 metres). The description of the phenomenon is similar in both, and the captain added an opinion of his own: 'Given the light conditions at the time I think it is highly probable that it was a satellite or space station etc that could reflect sunlight and/or moonlight'.

The office georeferenced the sighting with the Stellarium and CelesTrak programs and found several orbiting objects passing between 1:30 and 1:40 that day that 'could explain the reported observation' and matched the time and path described: the ERBS satellite, the Qarman satellite, 'Starklink 1107', the Soyuz MS-13 capsule and the International Space Station. It reproduces a CelesTrak screenshot with the station's track crossing Patagonia. Its conclusion: 'Owing to the close match in time and trajectory', the sighting was a conventional object in orbit around the Earth, 'such as the ERBS and VCC B satellites, but given the brightness and magnitude it was most probably the International Space Station'. It classified the case as 'Resolved' on 20 February 2020.

The case shows how a cockpit report gets resolved when the witness himself supplies the key. The captain described nothing extraordinary: he asked whether there was traffic, described a flashing light crossing to the east and, when he filled in the form, attributed it himself to a satellite or space station reflecting sunlight or moonlight. The geometry allowed it. In mid-December, at 50° south, the Sun was only some 16° below the horizon at that hour, so objects in low orbit were still lit, and the Moon was rising in the east-north-east (our own ephemeris calculation for 04:35 UTC). The International Space Station, whose orbit reaches 51.6° of latitude, passes over that part of Patagonia near the southernmost point of its track, where it is moving east, the same direction in which the captain saw the light disappear (a deduction).

What the report does not sort out is its own timeline. The first report gives 1:35 and the form 1:55, and the committee searched for passes between 1:30 and 1:40, the first report's window, without explaining why it set aside the captain's time. The CelesTrak screenshot it uses to illustrate the station's pass, stamped 04:26:36 UTC on 17 December, 1:26 local time, shows the station's marker over the southern Andes, near BODOM, and sunlit, with the Sun some 16° below the horizon. In other words, the station was passing over the aircraft nine minutes before the radio query; at some 7.7 kilometres per second, by 04:35 it was about 4,000 kilometres away, and by the 1:55 on the form much farther (a deduction). The identification therefore works if the sighting began some nine minutes before the query, which is possible if the captain asked about traffic when he was already watching the object, but not at the time given in either report. The report does not discuss this.

The list of candidates also contains errors that do not change the conclusion but that the report did not correct. According to Jonathan McDowell's satellite catalogue (GCAT), Soyuz MS-13 had been docked to the station since July 2019, and the small Qarman satellite was travelling inside it until it was released on 19 February 2020, so that night neither was an object separate from the station; and Starlink 1107 was launched on 7 January 2020, three weeks after the sighting. The conclusion also mentions VCC B, which is not on the list. And '1 o'clock' on a heading of 120 degrees points to about 150 degrees, not the 200 the report gives (a deduction).

What remains is the pilots of a single flight, whom the report refers to in the plural although it records only the captain's description, the control report with the audio from that same night, and an explanation the captain himself put forward and the committee backed with the match in time and path. There were no photographs and no radar record of the object, and the report mentions no collision-avoidance or onboard radar alerts. The committee closed the case as 'Resolved' two months later.