Below the radar: Could anyone else have known of Andreas Lubitz's plans when he took to the controls of his Germanwings flight?

In the past decade and a half, air travellers have become wearily used to the threat of terror attacks involving aeroplanes. We have accepted more stringent security measures at airports.

We understand the need to make cockpits impregnable. The need for armed air marshals on some flights to America is acknowledged, albeit reluctantly. Fear of flying has taken on a more logical expression.

By contrast, the air crash in the Alps this week appears to have resulted from an illogical act, one not driven by ideology, nor hate, but by irrationality caused by some psychological disorder – though its consequences are no less horrific. As things stand, it remains unclear precisely what motivated Andreas Lubitz’s calm and determined decision to fly an airliner and its passengers into a mountain. Investigators are focusing on his mental health amid reports that he had a history of serious depression and had been hiding an ongoing illness from his employers. Speculation will continue for as long as the families of victims demand answers, and it is vital that the authorities do all they can to establish the fullest available facts.

Mental health charities have been right to emphasise that simplistic assumptions about the link between Lubitz’s state of mind and his actions should be avoided. A great many people suffer from mental illness and only the tiniest minority pose a threat to the safety of others, in whatever walk of life. This week’s horror should not be allowed to exacerbate the stigma that can attach to the condition. But nor should the debate around Lubitz’s psychological condition detract from the tragic fact that his action led not only to his own death but also that of 149 people who had placed their lives in his hands.

Just as the attacks of 9/11 led to concerns about air passenger safety, so many will approach their next flight with renewed trepidation. That is understandable. Yet the risk that a pilot with murderous intent, or one who has been turned to senselessness by some other factor, might take control of an aircraft is not new. And removing all chance that it could happen again is nigh on impossible.

Nevertheless, it is right that airlines should reconsider the measures they have in place to ensure that the risk of malign or psychotic acts by air crew is as small as it can be. The shift to the “rule of two” already employed by many American carriers is an obvious response and one that will provide a considerable degree of reassurance. Calls for the installation of a cockpit lock override will be tempered by the fear that such a feature might make acts of terrorism by determined passengers more likely. It has even been suggested that personnel on the ground could play a more significant role, taking over controls if something appears to be amiss. But that idea too is fraught with potential difficulties and carries risks of its own.

As The Independent’s Simon Calder noted on Wednesday, despite several appalling disasters in recent times, there is no evidence that flying is becoming more dangerous per se. Indeed, with about 3.5 billion passenger journeys likely to be made this year, it is the safety of the aviation industry that is remarkable, not its perils. The tragedy in France this week needs to be seen in that context.

Amid all these debates, we must remember the families who are struggling to cope not just with the sudden and devastating loss of loved ones but with the realisation that a human hand is the cause. Explanations for Andreas Lubitz’s actions and assurances over future practices will not lessen their grief, and must not be permitted to undermine the dignity of their mourning.