Industry hazards

Hazard 1: The top-dressing material is not free-flowing

Controlled by: manufacturer; transport operator; driver, airstrip owner, and farmer.

1. Moisture can alter the flow characteristics of the material from the hoppers in top-dressing aircraft and in extreme cases, the particles of material can adhere to each other changing the nature of the material from one of freeflowing powder to large chunks of material. In some situations the throat of the hopper can be entirely blocked.
2. When excessive fineness of material is involved, the material may become compacted and immovable.
3. Aircraft hopper throat blockage can also occur due to the fertiliser containing large lumps, or debris from the storage site, for example: stones and rocks, earth clumps, sticks, vegetation and cowpats.

These situations can present a potential life-threatening hazard for the pilot of the aircraft, particularly when the pilot needs to discharge the payload during an emergency and cannot. This requires the fertiliser to be manufactured to, and maintained at a suitable standard until it is applied and it should be free-flowing and free from contaminants when placed in the hopper of the aircraft.

Chain of responsibility

Each party: manufacturer, supplier, transport operator, airstrip owner, farmer, loader driver, aerial operator and pilot, has responsibilities to ensure the fertiliser is in a suitable condition before delivery, while taking delivery, and while handling the product including loading and sowing, to ensure that the product is maintained in a free-flowing condition while in their possession.

Control of contaminants and moisture is vital to ensure flow characteristics are maintained. Appendix 1: Requirements for fertiliser storage covers these issues and provides an important source of information on the storage of fertiliser.

Hazard 2: Farm tracks and roads are unsuitable or in an unsafe condition

Controlled by: airstrip owner/farmer.

1. Culverts, crossings and bridges shall be able to withstand the gross weight of both the truck and trailer units in use.
2. Farm tracks and roads should be constructed and maintained to a standard fit for purpose.
3. Restrictions may need to be applied as to when farm tracks and roads can be safely used (for example due to weather conditions), and agreed between the transport operator and airstrip owner/farmer.

Hazard 3: Airstrip unsafe for use

Controlled by: airstrip owner.

1. Design limitations

The function of an airstrip is affected by numerous things, each of which can impact on the performance of the pilot and aircraft. The design and location of the airstrip may restrict the type of aircraft that can be used, reduce the maximum load that can be carried, or be so affected by weather that operations are restricted to set periods. The decision to use the strip within the airstrip design and location limitations lies with the aerial operator.

2. Inadequate airstrip maintenance

Accidents have occurred through remarkably small but nevertheless important and manageable oversights. Examples are:

• failing to stop on the airstrip because the grass was too long and wet - the aircraft slid off at the run way end point
• aircraft destroyed after its wheel struck a pothole caused by a rabbit
• aircraft hit a tree which had grown into the take-off path.

All of these instances cause severe damage to the aircraft involved and often fatal or serious injury to pilots. Airstrip position, length, slope, direction, surface condition, the proximity of fences and trees and stock and pest control, are all important in the management of airstrips.

Appendix 2: Top-dressing airstrip standards and specifications covers these issues and provides an important source of information needed to manage airstrip safety.

Hazard 4: Lack of training, information, supervision or communication

Controlled by: employers and employees.

• Staff performing work are not sufficiently trained and/or supervised.
• Staff are not communicating health and safety issues.

Ensuring that the staff performing work are trained and/or properly supervised is an employer's direct responsibility. The systematic review of work conditions is a responsibility shared by all parties to a work situation. When substandard conditions are identified, key information shall be shared with all relevant parties to determine an appropriate control prior to work continuing.

Manufacturers of fertilisers

Hazard 1: The top-dressing material is not free-flowing

Fertiliser that is not free-flowing can, in some situations, completely block the throat of the aircraft's hopper. This presents a potentially life-threatening hazard for the pilot of the aircraft, particularly when the pilot needs to discharge his payload during an emergency and cannot.

Control of contaminants and moisture is vital to ensure flow characteristics are maintained. See Appendix 1: Requirements for fertiliser storage.

Lime delivery

Manufacturing guidance and information

The flow properties of fertiliser, including lime, depend on particle size and size range, particle shape, compression (the amount of pressure applied to the bulk material) and whether the material is cohesive i.e. sticky. These properties of the bulk fertiliser can be measured.

No mixtures of fertilisers, either as supplied or mixed on site, should be used for aerial application unless it has been established that the flow properties of the resulting mixture will remain free-flowing at the time of use.

The farmer purchasing fertiliser should inform the supplier what method will be used to spread the fertiliser, for example, whether it will be spread by air or from a truck.

When the customer places the order the manufacturer and/or supplier should request information about the intended application method (aerial or ground spread) of the product. The manufacturer should ensure that a process is adopted in their order system which requires this information. It is the responsibility of the supplier of the fertiliser to ensure that the product is supplied in a free-flowing condition, according to the intended application method of the product.

An important factor when considering lime suitability for aerial sowing is the fineness of grinding or surface area of the lime particle. The surface area increases in almost direct proportion to the fineness of grinding. At any given constant weight, if the particle size is halved the surface area is doubled. This is a critical issue in establishing the amount of moisture that the material will hold and also the degree of compaction that the material will inherently have. Finer materials have a very high surface area to which water molecules will attach. Agricultural limestone usually has a wide range of particle sizes; this is a desirable feature unless too large a proportion of the particles is so coarse that, under most environmental conditions, little of the material will dissolve for many years.

The fineness of lime is measured by passing it through a series of standard sieves. Previous regulations (then administered by the Ministry of Agriculture and Forestry) controlling the fineness of grinding of agricultural lime to be used in aerial applications specified the following:

• at least 95 percent of the ground limestone to pass through a 2.0 mm sieve
• at least 50 percent of the ground limestone to pass through a 0.5 mm sieve.

While the farming community may desire limestone to be ground as fine as possible for better absorption, it should be recognised that very fine limestone carries with it an increased risk of compaction. In an aerial application situation, the material will be generally less free-flowing than a coarser grind which still complies with the specification above. In order to ensure that the material can remain free-flowing, controlling excessive fineness is very important. This was recognised by the fertiliser industry when powder superphosphate bulk fertiliser was implicated in many of the aircraft accidents which occurred while sowing super. As a result, pelletised superphosphate is now the normal form for that material for aerial application.

Manufacturers shall be aware of the requirement under Civil Aviation Rule Part 137 Subpart C - Special Flight Rules. This rule is printed below, and attention should be focused on 137.103 (a)(2).

"137.103 Maximum take-off weight

(a) Notwithstanding Part 91 and subject to paragraph (b), a pilot performing, or being trained to perform, an agricultural aircraft operation in an aeroplane must not take-off at a weight greater than the MCTOW prescribed in the aeroplane's flight manual unless—

(1) the pilot complies with the procedures listed in Appendix B; and

(2) the aeroplane is equipped with a jettison system that, in accordance with D.5, is capable of discharging not less than 80 percent of the aeroplane's maximum hopper load within five seconds of the pilot initiating the jettison action.

(b) Where there is a third party risk as defined in Appendix A, the pilot must determine the maximum take-off weight in accordance with 137.107 and 137.109."

While these rules relate to the aircraft itself, it obviously becomes important that fertiliser material, including lime, is manufactured so that the criterion for jettison is achievable. A material which is so fine that it compacts and does not flow freely may inevitably be implicated in discharge problems.

Control of particle size, moisture and storage

Any fertiliser placed into an aircraft must be completely free from any large lumps, foreign objects or debris, and be sufficiently dry and in a condition where it will flow freely from the aircraft hopper when discharged during flight.

It is the responsibility of the supplier to supply fertiliser (including for example, lime, sulphur or any other bulk solid to be applied by air) as above.

It is the responsibility of the farmer to store the material in a manner that ensures that the condition of the fertiliser remains free-flowing while in storage and that it continues to satisfy these requirements when being extracted from storage for use.

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