tie down your aircraft

Each year numerous aircraft are needlessly damaged by windstorms because of inattention to weather forecasts, negligence, or improper tiedown procedures. Windstorms may be broadly classified as cyclonic storms or low pressure systems, regional or localized terrain induced winds, thunderstorms or tornado induced winds and hurricanes. The best protection against windstorm damage is, of course, to fly the aircraft out of the impending storm area provided you have sufficient warning time. The next best protective measure is to secure the aircraft in a stormproof hangar or other suitable shelter. The remaining alternative is to assure that the aircraft is tied down securely. When securing your aircraft, it is considered good practice to fasten all doors and windows properly, thereby minimizing damage inside the aircraft. 

Engine openings (intake and exhaust) for both reciprocating and gas turbines should be covered to prevent entry of foreign matter. Pitot-static tubes should also be covered to prevent damage or entry of foreign matter. Make sure your neighbour's aircraft is also tied down. It is the mission of the NWS to help mitigate the threat to life and property from natural hazards through the issuance of tornado and severe thunderstorm watches and warnings. NWS meteorologists at the National Severe Storms Forecast Centre (NSSFC) monitor atmospheric conditions utilizing information from many sources and locations. When hazardous conditions are anticipated or detected, watches or warnings are issued.

Watches are issued by the NSSFC to indicate when and where severe thunderstorms and/or tornadoes are mast likely to occur. Watches are usually issued for areas about 140 miles wide, 200 miles long and generally 2 to 4 hours in advance of severe weather. Listen to the National Oceanic and Atmospheric Administration (NOAA) weather radios continuous broadcasts for the latest weather information directly from NWS offices, and use commercial radio or television for further information.

Warnings are issued by local NWS offices when severe thunderstorms or tornadoes are indicated by weather radar, weather observers or trained spotters. A warning describes an imminent risk from a tornado or severe thunderstorm in a relatively small area such as one or several counties. The key to damage avoidance or reduction is to be routinely weather conscious.

Be prepared for the worst conceivable windstorm conditions: pouring rain, gusty winds ranging from 30 MPH and up, for example intermittent sheets of water blowing across the runways, ramps, and parking areas, and lack of hangar facilities. With such conditions in mind, aircraft owners and operators should plan in advance by learning their aircraft manufacturer's instructions for tiedown; location and/or installation of tiedown rings for attachment of tiedown ropes; any special instructions for securing nosewheel type aircraft vs. tailwheel type aircraft; and manufacturer's charts and graphs denoting aircraft weights and relative wind velocities that would make varied tiedown procedures necessary for pending weather emergencies.

Any aircraft parking area should be equipped for three-point tiedowns. Aircraft should be tied down at the end of each flight to preclude damage from sudden storms. The direction in which the aircraft are to be parked and tied dawn will be determined by prevailing or forecast wind direction.

Aircraft should be headed into the wind, or as nearly as possible, depending upon the 1ocations of the fixed parking area mooring points. Spacing of tiedowns should allow for ample wingtip clearance. Spacing should be equal to the major axis (wingspan or fuselage length) of the largest aircraft usually operated plus 10 feet. After the aircraft is properly located, lock the nosewheel or the tailwheel in the fore-and -aft position.

Tiedown anchors for single engine aircraft should provide a minimum holding power (strength) of approximately 3,000 pounds each. The type of anchors in use varies depending upon the type of parking area--- whether for a concrete paved surface, a bituminous paved surface, or an unpaved turf area. Location of tiedowns are usually indicated by some suitable means, either white or yellow paint, or a painted tire which has been fastened into the ground, or surrounding the tiedown anchor with crushed stone. The tiedown anchor eye should not protrude more than 1 inch above ground.

Stake-driven tiedowns such as depicted above will almost invariably pull out when the ground becomes soaked from torrential rains which accompany hurricanes and some thunderstorms. Tiedown ropes capable of resisting a pull of approximately 3,000 pounds should he used. Manila ropes should be inspected periodically for mildew and rot. Nylon or dacron tiedown ropes are preferred over manila ropes. The objection to manila rope is that it shrinks when wet, is subject to mildew and rot, and has considerably less tensile strength than either nylon or dacron. Securing aircraft. Tie only at the tiedown rings provided for that purpose. Never tie to a strut itself. The practice of tying to lift struts has in itself caused frequent damage. Ropes slip to a point when even slight pressure may bend the struts. 

Allow for about 1 inch of movement, and remember that manila rope shrinks when it gets wet . Too much slack will allow the aircraft to jerk against the ropes. Avoid tightening the ropes too much. Tight tiedown ropes actually put inverted flight stresses on the aircraft, and many of them are not designed to take such loads. A tiedown rope holds no better than the knot. Anti-slip knots such as a bowline or a square knot are quickly tied, and easy to untie.

All flight controls should be locked or tied to prevent their banging against the stops. sane aircraft are equipped with integral gust locks operable from the cock- pit. On others, it may be necessary to use external padded battens (control surface locks) or secure the control wheel and rudder pedals in- side 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 nose-gear 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.

The following practices are designed for day-in- day-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. 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. Wherever possible, fly aircraft out of anticipated storm danger zones. If possible, hangar the aircraft in a stormproof hangar. 

The minimum recommended tiedown rope is one which will resist a pull of approximately 3,000 pounds. (Many users of plastic tiedown rape, 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.

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.

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.

Follow the manufacturer's tiedown instructions for each make and model aircraft. Another alternative 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.

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.

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 such aircraft.

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 takeoff with gust locks on is not only embarrassing but could prove to be 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.

The following practices are designed for day-in- day-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. 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. Wherever possible, fly aircraft out of anticipated storm danger zones. If possible, hangar the aircraft in a stormproof hangar. 

The minimum recommended tiedown rope is one which will resist a pull of approximately 3,000 pounds. (Many users of plastic tiedown rape, 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.

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.

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.

Follow the manufacturer's tiedown instructions for each make and model aircraft. Another alternative 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.

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.

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 such aircraft.

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 takeoff with gust locks on is not only embarrassing but could prove to be 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.

c) 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 instruct ions.

e) Install a rotor blade cover aver the tip of each main rotor. Secure a tiedown rope to each blade cover and the oth8r end of the rope to the applicable mooring point on the helicopter. Remember not to leave too much slack and to use anti-slip 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 anti-slip 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.

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, 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.