Before the airport opened at Chek Lap Kok, Professor Paul Wilkinson, a leading expert on the subject, warned about the constant danger of terrorist activity in civil aviation. Airports which seem the farthest removed from any threat are the soft targets that terrorists seek, and thus Hong Kong needs to remain on a high state of vigilance, he warned. In the light of those words, the current reassurances of both aviation authorities and airline personnel have a hollow sound. Twice in two weeks people have slipped past the guards and managed to board unguarded planes. That they were not members of any terrorist organisation is beside the point. The incidents show that security can be breached, and breached without great difficulty. Vigilance has had lapses of a fairly basic nature. In technological terms, Hong Kong International Airport is up there in the top league. Real guns and explosives may be readily detected by its gadgetry, but security relies on a marriage of technology and the human factor. In the days before opening, when Norman Shanks, chairman of the Airports Council International Security committee, was in charge of security at Chek Lap Kok, the human factor was given top priority. Mr Shanks gave evidence at the inquiry into the Lockerbie air disaster. He came away, he said, realising the importance of ensuring that airport staff truly understand what they are taught in their security training. Unarmed staff are defenceless against an apparently armed assailant, and it would obviously be undesirable to have every security guard carry a gun. But the fact that aircraft are parked on the tarmac with unguarded doors is a matter of great concern. If security is sacrificed partly because of an airline dispute with the Airport Authority, both sides should sit down now to reassess their priorities before transit passengers choose other routes where safety is not at issue. But whatever the reason for removing step guards, their absence appears to be a mistake.