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Aircraft Tie Down
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An aircraft tie-down scheme is designed to minimise the possibility of aircraft movement due to high winds or propeller/jet-efflux. Tie down is most likely to apply to aircraft up to about 12 tonnes12,000 kg
26,455.471 lbs for normal conditions in temperate latitudes but in the event of the risk of extremely high winds anywhere, this indicative maximum is unlikely to be applicable.
Each year numerous small aircraft are unnecessarily damaged due to the effects of strong winds or exposure to propeller/jet efflux from adjacent aircraft. This can be a consequence of inattention to weather forecasts or their inaccuracy. It may also be a consequence of inappropriate tie-down procedures. The decision to tie down or not needs to be taken with the weight of the aircraft involved relative to the expected maximum wind speed in mind.
When tie down is to take place, an aircraft should be positioned into the forecast mean wind direction and of significant change in this is expected during the period of tie down then arrangements to reposition the aircraft at some point may be necessary. In the case of small tail wheel aircraft, the opinion has sometimes been expressed that they should be tied down tail into wind but in this case, the installation of external Flight Control Locks would be essential as would the use of a tie down point at the tail.
- Structural damage to an aircraft.
- Failure to detect such structural damage caused prior to flight with the risk of loss of control.
- Hangar the aircraft.
- Fly it to another aerodrome where the forecast wind speed is less.
- Use a 3-point tie-down which uses either fixed tie down points or moveable, usually concrete, blocks and follow any instructions contained in relevant aircraft Manuals.
- If evidence of aircraft movement whilst tied-down is found, a diligent pre-flight inspection is called for and it may ne appropriate to seek suitably qualified engineering assistance.
- Ensure that all tie-down apparatus has been removed before any movement of the aircraft takes place.
The following is an extract from a real-life incident:
"As the aircraft took off from Runway 25, the tower Air Traffic Control Officer observed an object dangling from the tail. The object was subsequently identified as a car tyre filled with concrete, which had been used to tie down the aircraft on the ground. The pilot was informed and he landed the aircraft safely after completing a normal circuit. After landing, the aircraft was taxied clear of the runway and shut down before the tie-down weight was removed. A runway inspection was carried out before further use. The pilot reported that during the aircraft’s pre-flight inspection he had removed the tie down weights attached to the wings but had failed to notice the tie down weight attached to the tail”.
- Other Aircraft. Adjacent aircraft for which have not been appropriately secured has been known to lead to sufficient movement for impact damage to a correctly-secured adjacent aircraft to occur.
- Flying Debris. Damage from airborne debris - both unsecured items and detached pieces of poorly maintained buildings - has been known to cause damage to correctly tied down aircraft.
- Unless it can be guaranteed that all aircraft can be hangared if necessary, aerodromes handling smaller aircraft should provide permanently installed and appropriately positioned tie down rings for at least some parking positions. If this is not possible then tie down blocks of appropriate weights and the means to move them around should be provided.
- If a fully satisfactory tie down solution is not available then consider taking advantage of any available shelter and seek local advice in this respect if possible. If a relatively sheltered place cannot be found, it may be possible to park a large truck or tractor in front of the aircraft to help break up the airflow at the aircraft, although this action can sometimes introduce an additional risk by exposing the aircraft almost simultaneously to a range of wind velocities.
- Where tie down facilities are not available, it will be necessary to use a set of pickets which should be carried in the aircraft if a need for their use is anticipated. A picket set should include a number of steel stakes, a mallet and ropes of appropriate length, all stowed together.
- An article published in the New Zealand CAA magazine 'Vector' discusses Light Aircraft Tie-Down Techniques in detail.