SRM for the aircraft. Normally, a similar repair is illustrated,  and the types of material, rivets, and rivet spacing and the  methods and procedures to be used are listed. Any additional  knowledge needed to make a repair is also detailed. If the  necessary information is not found in the SRM, attempt to  find a similar repair or assembly installed by the manufacturer  of the aircraft. To maintain the float in an airworthy condition, periodic and  frequent inspections should be made because of the rapidity  of corrosion on metal parts, particularly when the aircraft is  operated in salt water. Inspection of floats and hulls involves  examination for damage due to corrosion, collision with  other objects, hard landings, and other conditions that may  lead to failure.  NOTE: Blind rivets should not be used on floats or amphibian  hulls below the water line. Sheet-metal floats should be repaired using approved  practices; however, the seams between sections of sheet  metal should be waterproofed with suitable fabric and sealing  compound. A float that has undergone hull repairs should be  tested by filling it with water and allowing it to stand for at  least 24 hours to see if any leaks develop.  [Figure 4-178] Some of the flight controls of smaller general aviation aircraft  have beads in their skin panels. The beads give some stiffness  to the thin skin panels. The beads for the repair patch can be  formed with a rotary former or press brake.  [Figure 4-179] Damage to metal aircraft skin that exceeds repairable limits  requires replacement of the entire panel.  [Figure 4-180]  A  panel must also be replaced when there are too many previous  repairs in a given section or area. In aircraft construction, a panel is any single sheet of metal  covering. A panel section is the part of a panel between  adjacent stringers and bulk heads. Where a section of skin  is damaged to such an extent that it is impossible to install  a standard skin repair, a special type of repair is necessary.  The particular type of repair required depends on whether the  damage is repairable outside the member, inside the member,  or to the edges of the panel. For damage that, after being trimmed, has 8 1 ⁄ 2 rivet diameters or  more of material, extend the patch to include the manufacturer’s  row of rivets and add an extra row inside the members. For damage that, after being trimmed, has less than 8 1 ⁄ 2  manufacturer’s rivet diameters of material inside the  members, use a patch that extends over the members and an  extra row of rivets along the outside of the members.  For damage that extends to the edge of a panel, use  only one row of rivets along the panel edge, unless the  manufacturer used more than one row. The repair procedure  for the other edges of the damage follows the previously  explained methods. The procedures for making all three types of panel repairs  are similar. Trim out the damaged portion to the allowances  mentioned in the preceding paragraphs. For relief of stresses  at the corners of the trim-out, round them to a minimum  radius of ½-inch. Lay out the new rivet row with a transverse  pitch of approximately five rivet diameters and stagger the  rivets with those put in by the manufacturer. Cut the patch  plate from material of the same thickness as the original or  the next greater thickness, allowing an edge distance of 2 1 ⁄ 2  rivet diameters. At the corners, strike arcs having the radius  equal to the edge distance.  Chamfer the edges of the patch plate for a 45° angle and form  the plate to fit the contour of the original structure. Turn the  edges downward slightly so that the edges fit closely. Place  the patch plate in its correct position, drill one rivet hole, and  temporarily fasten the plate in place with a fastener. Using a  hole finder, locate the position of a second hole, drill it, and  insert a second fastener. Then, from the back side and through  the original holes, locate and drill the remaining holes.  Remove the burrs from the rivet holes and apply corrosion  protective material to the contacting surfaces before riveting  the patch into place. As discussed earlier, lightning holes are cut in rib sections,  fuselage frames, and other structural parts to reduce the  weight of the part. The holes are flanged to make the web  stiffer. Cracks can develop around flanged lightning holes,  and these cracks need to be repaired with a repair plate.  The damaged area (crack) needs to be stop drilled or the  damage must be removed. The repair plate is made of the  same material and thickness as the damaged part. Rivets are  the same as in surrounding structure and the minimum edge  distance is 2 times the diameter and spacing is between four  to six times the diameter.  Figure 4-181  illustrates a typical  lightning hole repair. 4-99 Floats Corrugated Skin Repair Replacement of a Panel Inside the Member Edges of the Panel  Repair of Lightning Holes Outside the Member 