A number of members have been invited to contribute to a general discussion on the value of meteorology to navigation. It is hoped to follow Mr. Williams' contribution with others dealing with different aspects of the subject.

Years ago there was weather in which birds and airmen alike walked. Now, although operations through particular airports affected by below-minima weather may be interrupted, airline services are rarely cancelled because of weather en-route. As aircraft tend to fly faster and higher, and navigational aids slowly improve, the weather information required by the short-range operator tends to be conditioned by the question: Can my aircraft operate through airport X at time T? The long-range operator is still interested in two other questions: What route will give the most favourable component, and What is that component? Having the meteorologist's answer to these and other, less vital, questions, the operator plans his flight on the assumption that the forecast is quite correct and equips and fuels his aircraft on the assumption that it is wholly false. The operator has learned to compensate for the errors of forecasting; possibly all the airline accidents in recent years in which unexpected weather deterioration played a major part could have been avoided with sound airmanship. The most realistic way, therefore, to consider the value of forecasting to airline operation is to attempt to evaluate the cost to operators of the measures they take to protect life and equipment against forecast error and speculate on what would happen if no forecasting were attempted.