For aerial photography to be successful, the primary requisite is that the survey area should be completely cloudless. Camera filters can film through haze of reasonable density, but cloudless conditions are imperative. Completely cloudless conditions can be rare events, especially in places such as Papua New Guinea, where it was acceptable to photograph over minimum cloud patches. But it was then usual for the area to be photographed a second time with the expectation that the area obliterated by cloud on the first occasion probably would be clear of cloud on the second.

Regulations required that we observe flight time limitations daily, weekly, monthly and yearly. These limitations were usually not restrictive. For example, the monthly maximum was 100 hours and the annual maximum flight time limitation was 1000 flying hours. On survey flying, about 500 hours annually was about the usual number flown under normal survey conditions.

At times our crew would have two separate operations to perform. We would rise early for an oil survey flight to make the most of calm conditions for the magnetometer, and this flight would frequently be completed early because of turbulence. We would be back on the ground by 8 am and sometimes earlier. We would then refuel the aircraft, remove the magnetometer and install the camera for high level (for those days) photography. We would then be airborne again by about 9 am if the weather was cloudless and climb to 25,000 feet for perhaps a full day's photography of 5 hours and 45 minutes. It was to cover these rare occasions when we didn't want to miss out on repeated days of suitable photographic weather, especially after the flight time of regular oil survey flights, that Adastra obtained a concession from the then Department of Civil Aviation to the effect that we could fly 120 hours in any one month, providing we did not fly more than 200 hours in two consecutive months.

Flying is, for most pilots, an enjoyable occupation and it was no hardship to fly to the maximum allowable, especially when it occurred so rarely. It has been only in recent weeks when looking through my log book to check the accuracy of dates etc. I noticed during the month of June 1963 I flew 120 hours and 15 minutes! (It would probably have rendered the aircraft insurance invalid had we pranged during those 15 minutes!)

Wal Bowles
25th August 2004.