All flight controls should be locked or tied to prevent their CONTROL SURFACE banging against the stops. Some LOCKS aircraft are equipped with integral gust locks operable from the cockpit. On others, it may be necessary to use external padded battens (control surface locks) or secure the control wheel and rudder pedals inside the cockpit. When using external surface locks, it is advisable that red streamers, weights, or a line to the tiedown anchor be fastened to the locks.
This will provide a means of alerting airport service employees and pilots to remember to remove the external locks prior to takeoff. Secure ailerons and rudders in neutral. Tailwheel type aircraft headed into the wind should have their elevators secured in the "up" position by securing the control column or "stick". Tailwheel type aircraft "tailed" into the wind should have their elevators secured in the "down" position by securing the control column or "stick". Set and lock wheel brakes.
Chocks should be placed and secured fore and aft each wheel. Wooden chocks may be secured by nailing a cleat from chock to chock on each side of each wheel.
Ropes may be substituted if wood cleats are unavailable. A brick or piece of 2 x 4 are poor excuses for good chocks.
on tricycle gear aircraft, secure a tiedown line through the nosegear tiedown ring.
In addition, secure the middle of a length of rope to the tiedown ring in the tail section. Pull each end of the rope away at a 45° angle and secure to ground anchors at each side of the tail. Elevators should be secured parallel to the ground (neutral position). It is good practice to also secure the flaps, especially if the aircraft is tailed into the wind.
NOSE WHEEL Par 7 13
8. RECOMMENDED PRACTICES. The following practices are designed for day-inday-out use regardless of the inconvenience they might entail. These practices are principally for protection of light and medium weight aircraft and result from experiences with the storms of the past. Adoption of the following recommendations should materially reduce aircraft damage from windstorms.
a. Partially disassembled aircraft which are outdoors, particularly light aircraft with engines removed, should be hangared as soon as storm warnings are received. Loose wings should never be tied against a fuselage; they should be stored inside a hangar.
b. wherever possible, ily aircrait out of anticipated storm danger zones.
If possible, hangar the aircraft in a stormproof hangar.
c. The minimum recommended tiedown rope is one which will resist a pull of approximately 3,000 pounds. (Many users of plastic tiedown rope, yellow polypropylene, 1/2-inch and larger, reported little or no rope failure because of its elasticity. In some instances, nylon and hemp rope failed. In others, steel cables were snapped while hemp lines, due to their elasticity, held. In many cases, both hemp and steel cable tiedowns failed due to chafing.)
d. A single row of properly secured sandbags or 2x2's (spoiler boards) on the top of a wing's leading edge will serve as an effective spoiler and reduce the lifting tendency of the wings. Do not overload the wings with sandbags. If the anticipated winds will exceed the lift-off speed of the aircraft wings, then the makeshift spoilers should run the entire length of the wings. The 2x2 homemade spoiler is very easily constructed and may be used for all types of light aircraft. Drill a number of 3/8-inch holes across the length of the 2x2.
Cement a strip of 1-inch foam rubber to the entire length of the 2x2. This will prevent damaging the wing's surface. Avoid nailing the foam rubber to the spoiler since the nailheads may damage the wing's skin.
8 ×д • • → waterproof cement
• 1-in. foam rubber Thread a length of nylon rope through each of the drilled holes.
To facilitate threading the nylon rope through the holes, it is suggested that the ends of the lines be seared. This will prevent fraying of the ends to be threaded through the 3/8-inch holes.
14 Par 8
To prevent the spoiler from shifting position due to the wind, it is suggested that knots be tied in the rope on either side of the drilled holes. The spoiler should then be tied onto an aircraft's wings at the 25 percent chord point. To prevent damaging the wing's leading and trailing edges, it is suggested that a piece of foam rubber, or carpet, or even rags be placed under the nylon rope before tying. Some people may like to substitute bungee (elastic) cords for the long lengths of nylon rope.
e. Follow the manufacturer's tiedown instructions for each make and model aircraft.
9. ALTERNATE METHODS. Another means for tying down aircraft of various types and sizes is by utilizing continuous lengths of parallel wire ropes passed through U-bolt anchors and fastened at the ends of the line with wire rope clips. Tiedown chains are attached to the wire rope with roundpin galvanized anchor shackles. This allows the tiedown chains to "float" along the wire rope and gives a variable distance between anchor points so that a variety of large, medium, and small aircraft can use a vertical tiedown without loss of space.
The vertical anchor significantly reduces impact loads that may occur during gusty wind conditions.
TYPICAL AIRCRAFT TIEDOWN USING A WIRE ROPE SYSTEM The distance between wire ropes will depend upon the types of aircraft which will use the tiedown area. This distance can vary from 22 feet and upward.
Par 8 15
The diagram on the left shows a proper vertical anchor using wire rope tiedown line, straight link coil chain for connection between the wire rope and aircraft wing. One link on the free end is then passed through a link of the taut portion and a safety snap is used to keep the link from passing back through. Any load on the chain is borne by the chain itself instead of the snap.
Still another means of securing an aircraft is with tiedown cables, one at each wing and the third at the tail section. One end of a tiedown cable is secured with a snaphook to the tiedown anchor eye protruding above ground; the other end is hooked through the tiedown rings installed on the aircraft. Cable slack is taken up with an adjustable locking device.
10. SECURING MUTIENGINE AIRCRAFT. Multiengine aircraft will obviously require stronger tiedown facilities because of the additional weight of these aircraft.
The anchors should be capable of a holding power of 4,000 pounds each for the lighter executive twin-engine aircraft. Much higher load capacity would be required for the heavier transport type aircraft. Do not depend on the multiengine aircraft's weight to protect it from damage by windstorms. It is quite possible for a sudden, severe windstorm to move, damage, or even overturn 16 Par 9
Multiengine aircraft should, therefore, always be tied down and chocked when they are to be left unattended for any length of time. Gust locks should be used to protect control surfaces. Be sure that gust locks are foolproof; a disastrous. If the landing gear makes use of the down lock safety pins, then these pins should be inserted when the aircraft is being secured.
SECURING HELICOPTERS. Structural damage can occur from high velocity surface winds. Therefore, if at all possible, helicopters should be evacuated to a safe weather area if tornado, hurricane, or winds above 65-75 mph are anticipated. If helicopters can be hangared, do so. If not, they should be tied down securely. Helicopters that are tied down properly can usually endure winds up to approximately 65-75 mph. Winds in excess of 75 mph will probably cause damage to helicopters. When high winds are anticipated, and helicopters are to be tied down, they should be secured as follows:
a. Head the helicopter in the direction from which the highest forecasted wind or gusts are anticipated.
b. Spot the helicopter slightly more than rotor-span distance from other aircraft.
Set and lock wheel brakes. Place wheel chocks fore and aft of all wheels (if available). Secure the chocks by nailing wood cleats from chock to chock on each side of each wheel. Ropes may be substituted if wood cleats are not available.
d. Position the main rotor blades and tie them down in accordance with the manufacturer's instructions.
e. Install a rotor blade cover over the tip of each main rotor. Secure a tiedown rope to each blade cover and the other end of the rope to the applicable mooring point on the helicopter. Remember not to leave too much slack and to use antislip knots when tying the mooring ropes.
f. Fasten the tiedown ropes to the fuselage mooring points and extend them to the ground mooring anchors. Provide sufficient slack and use antislip knots, such as square or bowline knots.
g. Place the tail rotor in a vertical position and install a cover over the lower blade tip. Tie the lower blade cover rope to the tail skid to prevent possible damage by flapping tail blades.
h. Close doors, windows, and exterior access panels.
i. Follow the manufacturer's instructions for each make and model helicopter.
Par 10 17
7/12/83 AC 20-350
SECURING HELICOPTER BLADES AND FUSELAGE
• MOORING LINE FOR
ROTOR BLADE
- TIP SOCK
GROUND LINE
- SEE DETAIL "A" DETAIL "A" FT NOTE
MOORING POINT LOCATION FOR DEAD-MAN ANCHOR ON UN- PINED AREA. OPTIMUM TIEDOWN IS SHOWN BY DOITED
• GROUND MOORING ANCHOR
HELICOPTER MOORING POINT Par 11
AC 20-35C 7/12/83
12. SECURING SEAPLANES AND AIRCRAFT ON SKIS. Aircraft mounted on floats or skis should be secured in the usual manner--to tiedown anchors or "deadmen" sunk under the water or ice. When warning of an impending storm is received, some pilots have been known to partially flood the floats of their aircraft, thereby partially sinking the aircraft. In addition, the aircraft is tied down securely to anchors. Seaplanes moored on land have been saved from high-wind damage by filling the floats with water in addition to tying down the wings. Pilots 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. Although the techniques mentioned in this paragraph are not recommended practices, they are cited here because they have proven effective in preventing damage from sudden windstorms.
Extreme care must be taken to reverse the effects of any such measures prior to operation of the aircraft.
13. CONCLUSION. The simplest way to prevent windstorm damage to your aircraft is to fly it out of any impending storm area provided there is sufficient warning time. If that is impossible or impractical, shelter the aircraft in a stormproof hangar. Should this prove impossible, then tie your aircraft down securely. Aircraft parked outdoors should be tied down securely after each flight. Use the tiedown techniques discussed in this advisory circular.
to tie a bowline or a square knot during fair weather; do not wait until the wind and rain are adding to your difficulties. Should you desire additional information, we suggest that you contact the manufacturer for specific tiedown instructions for your aircraft.
M. C. Beard Director of Airworthiness Par 1z 19