You must use your knowledge, ability, and experience to plan an aircraft structural repair that involves riveting. Each rivet must be selected and driven in a precise manner to meet the riveting specification. Some of the specifications are rivet spacing and edge distance, diameter of the rivet hole, aerodynamic smoothness, and size of the rivet bucktail. These can be accomplished only through determination, practice, and accurate manipulation of all layout and riveting equipment.

The following rules should govern your selection and use of rivets:

1. Replacements must not be made with rivets of lower strength material unless they are larger than those removed. For example, a rivet of 2024 aluminum alloy should not be replaced by one made of 2017 aluminum alloy unless the 2017 rivet is a size larger. Similarly, when 2117 rivets are used to replace 2017 rivets, the next larger size should be used.

2. When rivet holes become enlarged, deformed, or otherwise damaged, you should use the next larger size as replacement.

3. Countersunk-head rivets should be replaced by rivets of the same type and degree of countersink, either AN426 or MS20426.

4. All protruding-head rivets should be replaced with universal-head rivets, either AN470 or MS20470.

5. Rivets less than three thirty-seconds of an inch in diameter should not be used for any structural parts, control parts, wing covering, or similar parts of the aircraft.

6. Minimum rivet diameter is equal to the thickness of the thickest sheet to be riveted.

7. Maximum rivet diameter is three times the thickness of the thickest sheet to be riveted.

8. The proper length of rivet is an important part of the repair. If the rivet is too long, the formed head will be too large, or the rivet may bend or be forced between the sheets being riveted. If the rivet is too short, the formed head will be too small or the riveted material will be damaged. The length of the rivet should equal the sum of the thickness of the metal plus 1 1/2 times the diameter of the rivet, as shown in figure 13-43. The formula for determining rivet length is as follows: