Beira in February is hot, wet and low, a port city on a flat coast where the Pungwe river meets the Mozambique Channel, and in 1988 it was a city in a civil war, with the airport one of the few places in it that ran to a timetable. On the afternoon of 11 February the men in the control tower noticed something over the sea to the south that did not belong to the timetable, and they went on noticing it for three hours.

At nine minutes past six a LAM Boeing 737 came in to refuel on its way from Quelimane, up the coast, to Maputo. Its captain, Simplício Pinto, looked where the tower was looking and saw it too: a shape like a wing parachute, or a flying mattress, giving off a hard fluorescent light. The tower told him they had first seen it at three o’clock, and that the air force radar had it.

Pinto refuelled, boarded his passengers, and took off at twenty to seven. Then he did something most airline captains would not: he turned towards it and climbed. At eleven thousand feet the light was bright enough to dazzle him. He could make out three separate lights on it, like searchlights, set in a triangle. His co-pilot and his chief stewardess, Isabel Lobo, were looking at the same thing. He asked whether anyone aboard had a camera. Out of a hundred and fourteen passengers, nobody did.

So he signalled. He switched on the landing lights on the port side, off, on, off. The object began to climb, vertically, and its lights dimmed as it went. Pinto looked for it on the aircraft’s weather radar and found nothing. He took the 737 up to twenty-four thousand feet and it was still above him, off the port wing, and it stayed there, higher than he could go, for the forty-five minutes it took him to tire of the chase and turn for Maputo. It was enormous, he said, and it had seemed to be stationary south of Beira the whole time.

Cynthia Hind wrote the case up in the third issue of UFO Afrinews and did the sensible thing, which was to suspect a balloon. There was a class of stratospheric research balloon in service then, forty metres across, brilliantly reflective, lit on both sides, that circled the southern hemisphere on the high winds for weeks at a time, and which had been mistaken for craft before. A balloon at very high altitude at sunset stays lit long after the ground has gone dark, shines like a lamp, and will appear to hang motionless while an aircraft climbs uselessly beneath it. That class of balloon carried two lights, though, not three in a triangle, and none of them climbed on command. Hind wrote to the CSIR in Pretoria to ask whether any such balloon had been over Mozambique that week. She got no reply, and nothing from NASA either. Timothy Good put the case in his UFO Report for 1990, where it has sat since.

There is a small mystery inside the larger one, which is the three hours. A balloon drifting on the stratospheric wind would not have stayed south of Beira from three in the afternoon until dark. The tower’s log, if it survives, would settle a good deal. LAM still flies the Quelimane run.