Crack, Scratch, Gouge And Corrosion - Cessna 510 Mustang Structural Repair Manual

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General

Damage, as considered in this manual, is a cross-sectional area change or permanent distortion of a structural member. It

is classified in the following three categories: allowable damage, repairable damage, or damage necessitating

replacement of damaged parts.

Use good judgment in determining the type of significant damage to flat stock structural material. The terms, dent, crease,

abrasion, gouge, nick, scratch, crack and corrosion, referred to elsewhere in the manual, are defined below as a guide for

this determination, particularly with respect to the external skin of the airplane:

(1) Dent - A dent is normally a damage area which is depressed with respect to its normal contour. There is no cross-

sectional area change in the material. Area boundaries are smooth. Its form is generally the result of contact with a

relatively smoothly contoured object.

NOTE:

(2) Crease - A damage area which is depressed or folded back upon itself in such a manner that its boundaries are

sharp or well defined lines or ridges. Consider it to be the equivalent of a crack.

(3) Abrasion - An abrasion is a damage area of any size which results in a cross-sectional area change due to scuffing,

rubbing, scraping or other surface erosion. It is usually rough and irregular.

(4) Gouge - A gouge is a damage area of any size, which results in a cross-sectional area change. It is usually caused by

contact with a relatively sharp object which produces a continuous, sharp or smooth channel-like groove in the

material.

(5) Nick - A nick is a local gouge with sharp edges. You must think that a series of nicks, in a line pattern to be the

equivalent of a gouge.

(6) Scratch - A scratch is a line of damage of any depth in the material and results in a cross-sectional area change. It is

usually caused by contact with a very sharp object.

(7) Crack - A crack is a partial fracture or complete break in the material with the most significant cross-sectional area

change. In appearance, it is usually an irregular line and is normally the result of fatigue failure.

(8) Corrosion - Corrosion, due to a complex electrochemical action, is a damage area of any size and depth which

results in a cross-sectional area change. Depth of such pitting damage must be determined by a cleanup operation.

Damage of this type may occur on surfaces of structural elements. Refer to paragraph on corrosion damage.

C. Use good judgment in the determination of significant cross-sectional area changes by proper visual measurement of both

depth (per paragraph allowable damage) and length of any type (or combinations) of damage mentioned above.

Allowable Damage

NOTE:

Refer to Typical Skin Repairs for limits.

Damage or distortion which can be permitted to exist as it is or which may be corrected by a simple procedure, such as

stop drilling cracks or smoothing out nicks, is classified as allowable damage. The extent of allowable damage for the

major assemblies and component parts is determined on individual cracks. An optical micrometer tripod base tool is

recommended for depth determination of such damage. This tool is manufactured by Air Cargo Equipment, Micrometer

Division, 1121 East Colorado Street, Glendale, California. Also, a standard depth gage (Dial Indicator Depth Gage,

illustrated in Figure 2) may be used to determine depth of damage. Procedure for use of the gage is described in the

paragraph Determine Degree Of Corrosion Damage.

Corrosion Damage.

CAUTION: No repair of corrosion damage to PSE structure is allowed without prior approval of a Cessna DER

authorized damage tolerance engineer. Refer to Principal Structural Elements - General.

(1) Classification of corrosion damage.

(a) Corroded: mild to moderate - This corrosion can be cleaned up by chemical and/or mechanical methods which

are not structural repair.

(b) Corroded: severe - This corrosion requires replacement of part or structural repair after cleanup of corrosion.

(2) Determine degree of corrosion damage.

Retain printed data for historical reference only. For future maintenance, use only current data.