The problem with low visibility operations is that the visual cues may be reduced to effectively zero, and hence there is an increased reliance on "synthetic" information. The dilemma faced by BEA was to find a way to operate without cues, because this situation occurred on its network with far greater frequency than on that of any other airline. It was particularly prevalent at its home base – London Heathrow Airport – which could effectively be closed for days at a time.