Farm Airstrips and Associated Fertiliser Cartage, Storage and Application - Safety Guideline
Appendix 1: Requirements for fertiliser storage
Weatherproof storage of fertiliser
Often fertiliser is delivered to a top-dressing operation and used virtually immediately and exposure to weather, and in particular moisture, is not a significant issue. However, moisture can be a problem if the fertiliser has to be stored on site for some time. Most top-dressing fertilisers such as lime and superphosphates are hygroscopic; they absorb moisture from the air, especially if the material is exposed to weather and rain. This characteristic is made worse when they are in powdered or granulated forms such as when they are used in agricultural aerial top-dressing operations. The absorption of moisture causes two problems:
- it increases the weight of the material and therefore makes it more expensive to sow; and
- it alters the flow characteristics of the material from the hoppers in topdressing aircraft and in extreme cases, can cause the flow to cease altogether. This presents a potentially life-threatening hazard for the pilot of the aircraft.
Providing a weatherproof storage area for top-dressing fertilisers can therefore reduce the cost of the operation and remove a very real hazard to safe top-dressing operations.
Example of good fertiliser storage facility
Above and below: Storage bins and frames for tarpaulin roof
Site guidance for fertiliser storage facilities
The fertiliser storage facility should be sited such that water flows away from the area.
- The area should provide unobstructed backing space for delivery and loader purposes. This will avoid truck and trailer units jack-knifing.
- The area around the entrance to the storage area should be compacted metal with good drainage, and graded to shed surface water away from the loading area and the airstrip.
- Careful consideration should be given to the site of the storage area in order to gain the most efficient operation in the terms of delivery of material to the site, and for aircraft loading.
- Careful siting of the loader movement area out of the turning circle of the aircraft will also avoid disrupted operating area surfaces which can damage the aircraft.
- Top-dressing aircraft can load up to 2 tonnes of fertiliser at a time depending on the type of aircraft, and the storage capacity should be commensurate with the scope of the likely operations. For example, if a farm normally requires 100 to 150 tonnes of fertiliser, a bin that holds only 25 tonnes will cause delays in the operation and/or result in fertiliser being stockpiled on the ground outside the bin with a high likelihood of contamination.
Design guidance for fertiliser storage facilities
The main requirement for any fertiliser storage facility is to keep the fertiliser in a free-flowing condition. Ensuring that the fertiliser does not become wet or otherwise contaminated is paramount. The facility should also be designed such that the fertiliser can be extracted using the conventional loading buckets currently in use.
The minimum design features of such a facility include:
- water- and weather-proof (i.e. with a tarpaulin, roof and doors/shutters)
- concrete floor which includes a damp course to prevent moisture entry
- a barrier at the facility entrance to prevent stock from entering.
Further recommended features include:
- concrete walls or equivalent structures that prevent moisture entry and are structurally suitable to contain the fertiliser while being loaded with current bucket loaders
- a recommended bin width of 5.5 metres (to suit the dimensions of commonly-used loading equipment).
A simple framework structure such as water pipe can provide a suitable structure for the perimeter of a storage facility. This can be used with a waterproof cover which overhangs the structure, down to ground level when the maximum amount of fertiliser to be used is present. The cover must be capable of being made taut to prevent water pooling on and around it to prevent moisture contamination of the fertiliser.
Storage facility suitability, maintenance and inspection
The suitability of a storage facility design should be agreed between the aerial operator and the airstrip owner/farmer.
The storage facilities should be kept and maintained in a condition such that fertiliser intended for aerial sowing remains in a condition that is fit for purpose.
A record should be kept of any maintenance carried out on the facility.
The fertiliser storage site may be inspected for suitability on request from owners, farmers, transport operators, top-dressing operators, pilots or loader/drivers. The inspection may be carried out by an appointed health and safety inspector who may refer to this guideline.
Fertiliser bin with sliding roof in back position for access
Appendix 2: Top-dressing airstrip standards and specifications
Introduction
The function of an airstrip, its layout and associated elements is to provide for safe and efficient aircraft landing and take-off. The design of these areas must take into account the operational and physical characteristics of the aircraft expected to use the strip.
- Airstrip width - Minimum 30m
- Runway width - Minimum 15m
- All stock removed (cattle 2 weeks prior to operation)
- Loading area
- Wind indicator
- Drop down fence at end of strip
- Dry free flowing fertiliser (Covered bin)
- Strictly no admitance to work area
Strip Length: Please check strip length requirements with your aerial operator. Fertiliser application costs will increase on airstrips of marginal length due to the need to carry smaller loads.
Definitions: agricultural aviation and airstrips
Airstrip: a defined area symmetrically including the runway that is intended:
- to reduce the risk of damage to aircraft running off a runway
- to protect aircraft flying over it during take-off or landing operations.
Manoeuvring area: that part of an aerodrome to be used for the take-off and landing of aircraft and for the surface movement of aircraft associated with take-off and landing; but does not include areas set aside for loading, off-loading, or maintenance of aircraft.
Obstacle: all fixed and mobile objects, or parts thereof, that may obstruct either the movement of an aircraft on the ground or protrude into an aircraft's take-off or landing path.
Runway: a defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft.
Threshold: means the beginning of that portion of the runway usable for landing.
Airstrip specifications
The essential requirement is that the place where aerial agricultural operations are being conducted is safe. To achieve that, it is important to consider all of the following factors in a holistic way.
Airstrip site
The site for a top-dressing airstrip should be selected carefully having regard to the farm location and prevailing wind.
The runway direction should be aligned as closely as possible with the prevailing wind in the area. In this respect, the Meteorological Service of New Zealand Ltd can provide information on prevailing area wind flows. Even a small amount of tailwind (e.g. 18 kph) can significantly increase the required take-off distance for a loaded aircraft, or alternatively, cause the pilot to have to significantly reduce the load to be carried.
Advice on siting an airstrip can be obtained from the New Zealand Agricultural Aviation Association or your local aerial operator.
Airstrip width
The desired strip width is 40 metres with a minimum of 30 metres if terrain or other obstacles make 40 metres unobtainable. The whole of the defined area of the strip should be suitably prepared for the needs of the aircraft that are expected to use it. Aircraft can depart the side of a runway unexpectedly for a number of reasons such as an unexpected crosswind or tyre or steering problems. The runway strip provides some safety margin for the pilot to either stop the aircraft or get it safely airborne.
Runway width
The minimum width of the runway itself should not be less than 15 metres.
Runway length
In determining runway length, a key objective is that the runway should be of such a length that a fully loaded agricultural aircraft of the type that will use the runway must be in controlled flight by the end of the runway when carrying its full legal load in nil wind and International Standard Atmospheric (ISA) conditions. A short runway length will impact upon the weight of the load that can be carried. Advice on the length/weight reduction for specific sites can be obtained from the New Zealand Agricultural Aviation Association or your local aerial operator.
Air density decreases as altitude increases and as temperature rises. Lower air density penalises pilots in three ways: The lifting ability of an aeroplane's wings decreases, the power produced by the engine decreases, and the thrust of a propeller, rotor or jet engine decreases.
Pilots use charts or calculators to find out how temperature and air pressure at a particular time and place affect the air's density and therefore aircraft performance. When the air's density is low, aircraft need longer runways to take off and land and they don't climb as quickly.
Based on the requirements for common agricultural aircraft and airstrip altitude, the following table provides the typical equivalent flat runway length that top-dressing airstrips should meet. It is expected that these guidelines will be followed where a new airstrip is being constructed or an existing airstrip is being improved; achievement of the maximum length practicable should be a key aim. Where an airstrip is shorter than suggested here, there may be restrictions on the type of aircraft that can use the airstrip and/or the weight of loads that can be carried by the aircraft. This does not mean that existing airstrips with lengths shorter than those suggested below are unsafe, but simply that they have reduced safety margins and therefore the pilot may need to reduce the load being carried and/or even cease operations to ensure that an appropriate level of safety is maintained; e.g. if environmental, airstrip, aircraft or task conditions change.
Suggested Flat Lengths — New Airstrips
| Feet above sea level | Suggested flat length of new airstrips |
|---|---|
| Up to 1000 feet above sea level | 600 metres |
| Up to 2000 feet above sea level | 650 metres |
| Up to 3000 feet above sea level | 750 metres |
These suggested lengths may be reduced if the airstrip has a slope. Advice on the length reduction for specific sites can be obtained from the New Zealand Agricultural Aviation Association or your local aerial operator. The following diagram depicts length compensation adjustments for various slopes.
Examples:
- A 450-metre-long airstrip with a 10 percent down-slope has an equivalent length of 550 metres. (Find 450 on the 'level' line. Follow the 450 line down until it intersects the 10 percent line. Follow the curve line back up to the level line: read off = 550 metres.)
- A 350-metre-long airstrip with a 20 percent down-slope has an equivalent length of 510 metres. (Find 350 on the 'level' line. Follow the 350 line down until it intersects the 20 percent line. Follow an approximated curve line back up to the level line: read off = 510 metres.)
An alternative table is shown below:
| Height above sea level | Flat strip | Slope: | |||
|---|---|---|---|---|---|
| 5% | 10% | 15% | 20% | ||
| Up to 1000 feet | 600 metres | 550 metres | 500 metres | 450 metres | 420 metres |
| 1000 to 2000 feet | 650 metres | 600 metres | 550 metres | 500 metres | 470 metres |
| Over 2000 feet | 750 metres | 700 metres | 650 metres | 600 metres | 570 metres |
Where strips do not meet the length and slope information specified the pilot shall, along with any other performance limiting factors, make the farmer/principal aware of the length limitation. Performance factors that the pilot will take into account are: the wind direction and speed; airstrip surface and condition; slope; and the pressure altitude and temperature (density altitude).
Information should be given to the farmer/principal with respect to the maximum safe load and any payload weight reduction, see the pilot checklist, Appendix 2a: Airstrip risk assessment checksheet.
The maximum slope along the length of the strip should not exceed 1 in 5 (20%). This means that for every 5 metres one moves horizontally, the land must not rise/fall more than 1 metre.
Runway surface and strength
The runway should have a smooth, consolidated surface free of bumps and hollows, and with a surface of dense, hard-wearing and deep-rooted turf, or other all-weather surfacing such as limestone or tar seal. Clover use should be minimised as it provides poor braking action and can degrade aircraft directional control.
The runway surface should be of sufficient strength for the take-off and landing of the aircraft types the runway is intended to serve.
The runway surface should be capable of taking a motor vehicle comfortably at 80 kilometres per hour.
The runway itself should have an evenly graded surface not higher than 200 mm above the level of the strip to allow water runoff and prevent washout from heavy rain.
The airstrip should be kept free of pests. Rabbit holes and diggings aid washouts and can severely damage the landing gear on an aircraft. Similarly, for other than airstrip inspections, vehicles should not routinely be used on the airstrip as ruts can also assist the formation of washouts.
Note: Where cattle are grazed on the airstrip, the surface shall be free of fresh cattle manure and any other damage to the surface as a result of grazing. Fresh manure is corrosive and can significantly degrade directional control of the aircraft and aircraft braking action. Sheep grazing should have minimal impact on a properly surfaced runway.
Loading area
A loading area of sufficient size to allow for the manoeuvring and loading of the aircraft should be provided. Some aircraft are unable to make very tight turns due to nose wheel steering geometry. There should be sufficient room to allow the aircraft to commence the take-off run once loaded without having to turn to line up.
The area should have a well compacted surface with good drainage and be sloped to shed water away from the runway. The surface strength must be such as to withstand the wheel loads of both the aircraft and the loader turning and manoeuvring, fully laden, in all weather conditions in which aerial top-dressing may take place, without causing significant wheel ruts.
Wind indicators (socks)
Variations in wind direction and strength have been significant factors in agricultural aircraft take-off and landing accidents. A wind direction indicator should be provided to aid the aircraft pilot to judge both the wind direction and velocity. These are commonly called windsocks. Wind indicators need not be highly technical; a simple length of red or orange ribbon attached to a pole can be quite sufficient.
Depending on the airstrip site and runway environment, the wind indicator should be positioned not closer than 40 metres to the side of the runway threshold, or if the strip can be used in either direction, then not closer than 40 metres to the side of the centre of the strip.
NOTE: The aircraft operator may provide their own indicator.
Fencing and obstacles
A fifth of agricultural aircraft accidents involve fence strikes[1].
The airstrip, storage and loading area should be completely fenced so that stock can be reliably excluded. A pilot may inspect the airstrip and immediate area for stock prior to the first landing; therefore there should be no bush stands or gullies in which stock can be obscured and later obstruct the runway without warning.
There should be no obstruction within 200 metres measured from each end of the runway, or from the landing threshold on a one-way runway.
Fencing within 200 metres of the runway threshold should be removed for the duration of the top-dressing operations. Any immovable obstruction within the 200 metres may require the pilot to use a displaced threshold thereby reducing the available runway length. In turn, this may limit the aircraft load and therefore require more runs to complete the task, so increasing the cost of the operation.
Once airborne, an aircraft has to accelerate and climb before turning and proceeding to the area to be fertilised. This airborne path should be clear of obstructions such as trees, poles and strung wires. When operating in hilly terrain, wind direction, speed and wind gusts can significantly affect the flight path of a loaded aircraft and may even cause it to descend. An obstructed take-off flight path presents a potentially lifethreatening hazard for the pilot of the aircraft.
There are occasions when for any reason, such as an obstruction on the runway, a pilot may overshoot from the landing approach. Even though the aircraft is generally not carrying a load at this stage of flight, an obstructed overshoot flight path presents a potentially life-threatening hazard for the pilot of the aircraft.
Public access
If there is a reasonable expectation of public access to either the fertiliser storage areas or the airstrip, or where operations are near to a public road, then the whole site should be protected by fencing and signs warning of aircraft operations.
Airstrip and facility suitability, maintenance and inspection
The suitability of an airstrip should be agreed between the aerial operator and the airstrip owner/farmer.
The airstrip and facilities should be kept and maintained in a condition that is fit for purpose. A record should be kept of any maintenance carried out on the airstrip and facilities.
A top-dressing airstrip may be inspected for suitability on request from owners, farmers, top-dressing operators, pilots or loader/drivers. The inspection may be carried out by an appointed health and safety inspector who may refer to this guideline.
Accreditation of aerial operators by the New Zealand Agricultural Aviation Association includes a requirement that the sites from which they operate provide for safe and efficient operations to be carried out.
Appendix 2a: Airstrip risk assessment checksheet
Available as a pdf [size: 38KB ] or word document [size: 46KB ]
Footnote:
1 Civil Aviation Authority Accident/Incident database