Aircraft Systems: Aircraft Tie Down Procedures

Aircraft Tie Down Procedures

Preparation of Aircraft

Aircraft are to be tied down after each flight to prevent damage from sudden storms. The direction that aircraft are to be parked and tied down is determined by prevailing or forecast wind direction. Aircraft are to be headed into the wind, depending on the locations of the parking area’s fixed tie-down points. Spacing of tie-downs need to allow for ample wingtip clearance. [Figure 1] After the aircraft is properly located, lock the nose wheel or the tail wheel in the fore-and-aft position.

Aircraft tie down
Figure 1. Diagram of tiedown dimensions

Tie-Down Procedures for Land Planes

Securing Light Aircraft

Light aircraft are most often secured with ropes tied only at the aircraft tie-down rings provided for securing purposes. Rope is never to be tied to a lift strut, since this practice can bend a strut if the rope slips to a point where there is no slack. Since manila rope shrinks when wet, about 1 inch (1") of slack needs to be provided for movement. Too much slack, however, allows the aircraft to jerk against the ropes. Tight tie-down ropes put inverted flight stresses on the aircraft and many are not designed to take such loads.

A tie-down rope holds no better than the knot. Anti-slip knots, such as the bowline, are quickly tied and are easy to untie. [Figure 2] Aircraft not equipped with tie-down fittings must be secured in accordance with the manufacturer’s instructions. Ropes are to be tied to outer ends of struts on high-wing monoplanes and suitable rings provided where structural conditions permit, if the manufacturer has not already provided them.

Figure 2. Knots commonly used for aircraft tie-down


Securing Heavy Aircraft

The normal tie-down procedure for heavy aircraft can be accomplished with rope or cable tie-down. The number of tie-downs are governed by anticipated weather conditions.

Most heavy aircraft are equipped with surface control locks that are engaged or installed when the aircraft is secured. Since the method of locking controls vary on different types of aircraft, check the manufacturer’s instructions for proper installation or engaging procedures. If high winds are anticipated, control surface battens can also be installed to prevent damage. Figure 3 illustrates four common tie-down points on heavy aircraft.

aircraft tie down
Figure 3. Common tie-down points

The normal tie-down procedure for heavy aircraft includes the following:
  1. Head airplane into prevailing wind whenever possible. 
  2. Install control locks, all covers, and guards. 
  3. Chock all wheels fore and aft. [Figure 4] 
  4. Attach tie-down reels to airplane tie-down loops, tie-down anchors, or tie-down stakes. Use tie-down stakes for temporary tie-down only. If tie-down reels are not available, 1⁄4" wire cable or 11⁄2" manila line may be used.

Aircraft die down
Figure 4. Wheels chocked fore and aft

Tie-Down Procedures for Seaplanes

Seaplanes can be moored to a buoy, weather permitting, or tied to a dock. Weather causes wave action, and waves cause the seaplane to bob and roll. This bobbing and rolling while tied to a dock can cause damage.

When warning of an impending storm is received and it is not possible to fly the aircraft out of the storm area, some compartments of the seaplane can be flooded, partially sinking the aircraft. Tie down the aircraft securely to anchors. Seaplanes tied down on land have been saved from high-wind damage by filling the floats with water in addition to tying the aircraft down in the usual manner. During heavy weather, if possible, remove the seaplane from the water and tie down in the same manner as a land plane. If this is not possible, the seaplane could be anchored in a sheltered area away from the wind and waves.


Tie-Down Procedures for Ski Planes

Ski planes are tied down, if the securing means are available, in the same manner as land planes. Ski-equipped airplanes can be secured on ice or in snow by using a device called a dead-man. A dead-man is any item at hand, such as a piece of pipe, log, and so forth, that a rope is attached to and buried in a snow or ice trench. Using caution to keep the free end of the rope dry and unfrozen, snow is packed in the trench. If available, pour water into the trench; when it is frozen, tie down the aircraft with the free end of the rope.

Operators of ski-equipped aircraft sometimes pack soft snow around the skis, pour water on the snow, and permit the skis to freeze to the ice. This, in addition to the usual tie-down procedures, aids in preventing damage from windstorms. Caution must be used when moving an aircraft that has been secured in this manner to ensure that a ski is not still frozen to the ground. Otherwise, damage to the aircraft or skis can occur.

Tie-Down Procedures for Helicopters

aircraft tie down
Figure 5. Example of mooring of a helicopter

Helicopters, like other aircraft are secured to prevent structural damage that can occur from high-velocity surface winds. Helicopters are to be secured in hangars, when possible. If not, they must be tied down securely. Helicopters that are tied down can usually sustain winds up to approximately 65 mph. If at all possible, helicopters are evacuated to a safe area if tornadoes or hurricanes are anticipated. For added protection, helicopters can be moved to a clear area so that they are not damaged by flying objects or falling limbs from surrounding trees.

If high winds are anticipated with the helicopter parked in the open, tie down the main rotor blades. Detailed instructions for securing and mooring each type of helicopter can be found in the applicable maintenance manual. [Figure 5] Methods of securing helicopters vary with weather conditions, the length of time the aircraft is expected to remain on the ground, and location and characteristics of the aircraft. Wheel chocks, control locks, rope tie-downs, mooring covers, tip socks, tie-down assemblies, parking brakes, and rotor brakes are used to secure helicopters. 



Typical mooring procedures are as follows:
  1. Face the helicopter in the direction that the highest forecast wind or gusts are anticipated. 
  2. Spot the helicopter slightly more than one rotor span distance from other aircraft. 
  3. Place wheel chocks ahead of and behind all wheels (where applicable). On helicopters equipped with skids, retract the ground handling wheels, lower the helicopter to rest on the skids, and install wheel position lock pins or remove the ground-handling wheels. Secure ground-handling wheels inside the aircraft or inside the hangar or storage buildings. Do not leave them unsecured on the flight line. 
  4. Align the blades and install tie-down assemblies as prescribed by the helicopter manufacturer. [Figure 6] Tie straps snugly without strain, and during wet weather, provide some slack to avoid the possibility of the straps shrinking, causing undue stress on the aircraft and/or its rotor system(s). 
  5. Fasten the tie-down ropes or cables to the forward and aft landing gear cross tubes and secure to ground stakes or tie-down rings.

Aircraft tie down
Figure 6. Securing helicopter blades and fuselage

Procedures for Securing Weight-Shift-Control

There are many types of weight-shift-controlled aircraft—engine powered and non-powered. These types of aircraft are very susceptible to wind damage. The wings can be secured in a similar manner as a conventional aircraft in light winds. In high winds, the mast can be disconnected from the wing and the wing placed close to the ground and secured. This type of aircraft can also be partially disassembled or moved into a hangar for protection.

Procedures for Securing Powered Parachutes

When securing powered parachutes, pack the parachute in a bag to prevent the chute from filling with air from the wind and dragging the seat and engine. The engine and seat can also be secured if needed.