Aircraft tiedown is a very important part of aircraft ground handling. The type of tiedown will be determined by the prevailing weather conditions. In normal weather a limited or normal tiedown procedure is used; but when storm conditions are anticipated, a heavy weather or storm condition tiedown procedure should be employed. Normal Tiedown Procedure Small aircraft should be tied down after each flight to preclude damage from sudden storms. The direction in which aircraft are to be parked and tied down will be determined by prevailing or forecast wind direction. Aircraft should be headed, as nearly as possible, into the wind, depending on the locations of the fixed, parking area tiedown points. Spacing of tiedowns should allow for ample wingtip clearance (figure 11-18). After the aircraft is properly located, lock the nosewheel or the tailwheel in the fore and aft position.

Tiedown Anchors

All aircraft parking areas should be equipped for three point tiedowns. This is facilitated at most airports by use of tiedown anchors installed in concrete parking areas. Tiedown anchors, sometimes called "pad eyes," are ringlike fittings installed when the parking area is poured. They are normally set flush with the surface of the concrete or no more than one inch above it. There are several types of tiedown anchors in use. The type selected is usually determined by the material used in aircraft parking areas, since it may be a concrete paved surface, a bituminous paved surface, or an unpaved turf area.

Location of tiedowns is usually indicated by some means such as white or yellow paint markings or by surrounding the tiedown anchor with crushed stone.

Tiedown anchors for small single engine aircraft should provide a minimum holding power (strength) of approximately 3,000 pounds each. Although this minimum can be achieved when stake driven tiedowns are used in dry or turfed areas, such stakes will almost invariably pull out when the ground becomes soaked from torrential rains which accompany hurricanes and some thunderstorms.

Tiedown Ropes

Tiedown ropes capable of resisting a pull of approximately 3,000 pounds should be used to secure light aircraft. Cable or chain tiedown is usually preferred for tying down large aircraft.

Manila ropes should be inspected periodically for mildew and rot. Nylon or Dacron tiedown ropes are preferable to manila rope. The objection to manila rope is that it shrinks when wet, is subject to mildew or rot, and has considerably less tensile strength than either nylon or Dacron. Various types of commonly used tiedown rope are compared in figure 11-19.

Tiedown Cable

Tiedown cables are often used to secure aircraft, especially in the case of large aircraft. Most cable-type tiedowns are accomplished with some form of tiedown reel designed for rapid and reliable securing of all types of aircraft. figure 11-20 illustrates the operation of a typical cable tiedown reel.

In A of figure 11-20 the cable is released by depressing the release lever to provide cable slack. One end of the cable is then attached to the aircraft tiedown ring and the other end to a tiedown anchor. The starwheel on the reel (B of figure 11-20) is then turned clockwise to remove excess slack from the cable. The locking handle is then secured to the bar when the cable has been adjusted for the desired tautness (C of figure 11-20). Finally, as shown in D of figure 11-20, the locking cam is secured to complete the tiedown procedure.

Tiedown Chains

The chain-type tiedown sometimes is used as a better and stronger tiedown to secure the heaviest aircraft. This tiedown assembly is composed of an all metal quick release mechanism, a tensioning device, and a length of chain with hooks (figure 11-21).