The spraying of crops using light aircraft or helicopters poses a number of problems or hazards to the agricultural aviation industry. The toxicity hazard to humans and to neighbouring crops, due to drift, have already been considered in detail in previous symposia and much information is available on this subject. Another hazard which has not received much prominence, possibly due to the lack of incidents, or the reporting of them, and which is associated with the handling of flammable liquids is that of a fire or explosion risk. This is particularly true for spraying operations; incidents arising from aeroplane or helicopter crashes are rather obvious and these are not considered in this paper. The paper attempts to describe hazardous conditions and what steps can be taken to minimise fire and explosion risks.

In this paper an attempt is made to outline the hazards which can arise, with particular reference to light aircraft, due to static electricity. Accidents, some of which are described in detail later, can and do happen, yet the precautions which should be taken to reduce the dangers are very easy to carry out. These precautions are detailed in the final section of this paper and it cannot be over emphasised that the habitual use of these simple techniques could well prevent a fire from being started with the resultant loss of an aircraft and the possibility of injury or death from such a fire.

Perhaps I had better start this paper by denning exactly what is meant by ultra high tensile steel. During the Second World War and for some years afterwards, 80 to 90 tsi (i.e. 180 to 200 ksi) ultimate tensile strength was considered to be the highest safe range at which structural steel could be used, due to the lack of sufficient toughness or ductility at higher strength levels. This lack of toughness and ductility is particularly important in applications such as landing gears, in the design of which it is often impossible to avoid conditions where the principal stresses are perpendicular to the grain direction: in such applications, adequate transverse toughness and ductility are vital necessities. In more recent years, steels of higher strength, combined with adequate toughness have been developed, and thus the term “uhts” has become to mean those structural steels capable of attaining a tensile strength of over 90 tsi (200 ksi), combined with adequate toughness. In practice, the current state-of-the-art is that landing gears are now being regularly manufactured in steel in the 122–134 tsi (275–300 ksi) range, while designers are asking for steels of still higher strength combined with adequate toughness (up to 220 tsi, 500 ksi), and claim that the gross weight of the aircraft could be substantially reduced if and when such materials become available. It is interesting to note, however, that although the strength of uhts has in general increased from 90 tsi in 1947 to 130 tsi (300 ksi) in 1970, there is no evidence of the future availability of stronger steels than this latter figure, i.e. it looks as though we are stuck with this strength level as a maximum for future applications.

The aviation industry over the past twenty years has experienced rapid growth and also considerable fluctuations about this growing trend. It is fluctuations about this trend, even though they may be of relatively short duration, which make or break airlines. In Table I(a) for instance, are shown the fluctuations about the trend of fares, load factor, international airline operating projects, aircraft investment and output. The institutional structure within which air travel operates is shown by the small variation in fares, while aircraft investment and profits show wide fluctuation. Reference to the last three columns shows the synchronised cycle in aircraft producer profits. We shall enquire into some possible courses of these fluctuations, and then examine the consequences of these fluctuations on used aircraft prices and financial performance of the airlines.

As there is apparently no expert in the world on “De-icing Runways from the Air”—and certainly not the author— the best start is to relate something of the difficulties of de-icing runways, the chemicals used and the rival methods of spreading them, and to leave it to the operators of agricultural aircraft to decide whether and how agricultural aviation can do a useful job in freeing runways from the menace of ice.

Clearly for the safety of landings and take-offs, runways should be kept clear of anything which reduces the coefficient of friction, whether this reduction is the result of plain wet, snow, ice or slush. It is the objective of the British Airports Authority in common with other airports, to remove precipitation so that one, to use the Canadian expression, “gets down to the black top”—even though one's runway is near-white concrete. When ice forms on an untreated runway, it is liable to key itself to the irregularities of the surface and become difficult to move. Therefore a good plan is to have deposited one's chemicals, when there is precipitation, before the temperature falls to freezing point or else early on in the fall before freezing is too firmly established. However, on occasions, precipitation, as everyone knows, occurs without being forecast or the temperature falls unexpectedly.

Agricultural flying is a highly competitive business in which the rate for the job appears to be continually dropping as more and more operators enter the field. In this environment, every piece of extra equipment must earn its keep either in terms of improved efficiency or improved safety and, as a result, the adoption of such things as modern navigational systems has lagged behind that in general aviation practice.

What then can a suitable electronic navigation system offer the agricultural flyer? First and foremost, immediate knowledge of his present position and secondly a clear indication of track made good. These two characteristics translate very quickly into a reduction in non-effective flying time both en route and while spraying, together with a marked improvement in application quality and control, to say nothing of reduced pilot fatigue and improvement in safety; features with appeal to operator, pilot and farmer alike.