Unless the fog dispersal trick had worked every time (highly unlikely)
Not so unlikely in fact. A friend of mine who flew Gnats at CFS on exchange duty from the RAAF, described a similar technique used to disperse snow from the runway at Little Rissington in the Sixties. He ws authorised to taxi the Gnat down the centre of the snow covered runway several times to clear a narrow path using the heat and jet blast from the engine. This enabled flying operations to resume.
Presumably the heat from Gnat jet blast would have affected any fog droplets if they were present? The heat from the two Spey (?) engines of the Caravelle would, I thought, have some effect in lifting the fog a few feet enough for the pilots to see along the runway at minimum RVR. Certainly the official accident report which was published in an ICAO document which I read, stated that the Caravelle involved in the fatal crash, was using this technique to aid fog dispersal