3 One cause of aircraft accident is ‘controlled flight into ground’. Predominantly, the reason for this is not mechanical failure but human failure such as pilot fatigue. Boeing, which dominates the commercial airline business, has calculated that over 60 per cent of all the accidents which have occurred in the past 10 years had flight crew behaviour as their ‘dominant cause’. For this type of failure to occur, a whole chain of minor failures must happen. First, the pilot at the controls has to be flying at the wrong altitude – there is only one chance in a thousand of this. Second, the co-pilot would have to fail to cross-check the altitude – only one chance in a hundred of this. The air traffic controllers would have to miss the fact that the plane was at the wrong altitude

(which is not strictly part of their job) – a one-in-ten chance. Finally, the pilot would have to ignore the ground proximity warning alarm in the aircraft (which can be prone to give false alarms) – a one-in-two chance.

(a) What are your views on the quoted probabilities of each failure described above occurring?

(b) How would you try to prevent these failures occurring?

(c) If the probability of each failure occurring could be reduced by a half, what would be the effect on the likelihood of this type of crash occurring?