Description

1. TASK 70-20-00-200-501 Inspection - General Information

   1. General

      1. Each part must be carefully inspected to determine its suitability for continued use. Verification of part identification is essential throughout overhaul and maintenance processes. Sufficient part identification (such as part number, serial number, heat code) control must be maintained when parts are disassembled. In addition to visual inspection for obvious surface conditions, appropriate fluorescent magnetic particle or fluorescent penetrant inspection must be done as specified for each part.

      2. Nondestructive inspection is a group of procedures that can be used to examine the quality and dimensions of components. These procedures do not cause damage or have an effect on the component and so the component stays serviceable. The different types of nondestructive inspection include visual, dimensional, penetrant, magnetic particle, eddy current, ultrasonic and X-ray. A special inspection procedure is necessary for ball and roller bearings, refer to TASK 70-29-00-220-501.

         NOTE

         Nondestructive inspection must be done by a person who is approved and has the correct experience.

      3. Types of Inspection.

         1. Visual inspection.

            1. Visual equipment can be used to magnify defects which would not usually be seen by eye. Visual equipment can also be used to get access to areas that can not be seen by the eye.

         2. Visual check.

            1. A visual check is used to determine that an item is fulfilling its intended purpose. It requires a visual evaluation of an assembly, sub-assembly or part to detect obvious damage, failure or irregularity, that is outside of normal in-service wear and confirms that the item is capable of continued service. This evaluation is made without magnification and does not require dimensional measurements.

            2. A visual check is applicable to modules, subassemblies and parts that are removed solely to gain access to parts that require repair or modification.

         3. Dimensional inspection.

            1. This type of inspection is used to measure the dimensions of components to check if they are serviceable. All engine components that move or turn must be inspected for correct dimensions at regular times as specified in the applicable Engine Manual. Measure parts carefully and accurately when dimensions are specified. It is permitted to round dimension as specified in the SPM TASK 70-22-02-290-501.

         4. Penetrant inspection.

            1. This type of inspection is used to find defects on the surface of components that are not porous. A fluid is applied to the surface of a component and is permitted to go in to the surface defects. The unwanted fluid not in the defect is then removed from the surface of the component. The fluid in the defect can then be seen by the eye or by ultraviolet light. If the surface defect has unwanted particles in it, the fluid can not get in to the defect sufficiently. This will result in a decrease in the defect indication.

         5. Magnetic particle inspection.

            1. This type of inspection is used on materials that have ferromagnetic properties, such as iron and steel. A magnetic field is caused in the part and a defect will cause a change in this field. This change causes a leakage field over the defect which attracts magnetic particles to give a defect indication. The types of defects that can be identified are cracks, seams, laps, nonmagnetic particles near the surface and folds.

         6. Eddy current inspection.

            1. This type of inspection is used to get information about a material, such as alloy type, hardness, heat treat conditions, thickness and cracks. A coil causes eddy currents in the part and a defect will cause a change in this eddy current field. This change can be read on a meter, a cathode ray tube or a recorder.

         7. Ultrasonic inspection.

            1. High frequency sound waves are transmitted in to a component by a transducer. A defect in the component will cause a reflection of the sound back to the transducer. This data is usually shown on an oscilloscope. The correct selection of the transducer frequency will permit inspection of the surface, back surface and the internal of a component.

         8. X-Ray inspection.

            1. X-rays and gamma rays can be used to find defects in materials and components. The defects are shown by a procedure that converts radiation into a visual display, usually shown on film. This display gives a permanent visual record of the internal defects of a component. This procedure is used for internal inspection of castings, welds, components and assembled components. The inspection of different metals, both ferrous and nonferrous, ceramics and plastics is possible with this procedure. Radiography will show some types of internal defects in materials that are not transparent but it can not show all types of defects.

   2. Round-Off Rules

      1. Because IAE dimensions and quantities start as values in U.S. units (and because these values are approved as design limits for the safe and correct operation of engine parts), it is necessary to have the U.S. unit tolerance control the limits of the metric equivalent.

         1. When U.S. limits are at a certain level of accuracy, their metric equivalents cannot be less than the initial U.S. minimum or more than the U.S. maximum.

         2. The round-off rules for metric equivalents are different for a large tolerance (more than 0.006 in. (0.152 mm)) than for a small tolerance (0.006 in. (0.153 mm) or less).

      2. Large tolerance (more than 0.006 in. (0.152 mm)).

         1. Example: 1.495 in. - 1.504 in. is converted to (37.973 mm - 38.202 mm) by the IAE metrication program. It is possible that this is more accurate than necessary.

         2. The last digit of the minimum is less than 5, so it is permitted to omit this digit and let the minimum become 37.97 mm. The last digit of the maximum is also less than 5, so the maximum can become 38.20 mm. The approved tolerance (after round-off) is 37.97 mm - 38.20 mm. If the last digit of a value is 5 or more, the next to the last digit increases by one: 38.205 mm would get a round-off to the next higher number, or 38.21 mm.

      3. Small tolerance (0.006 in. (0.153 mm) or less).

         1. In small tolerance conversions, the S.I. units are not permitted to be out of the initial U.S. limits. An S.I. minimum must not be less than a U.S. minimum, and a S.I. maximum must not be more than a U.S. maximum. This is to keep parts and mating fits in limits and to keep gaging systems compatible.

            1. Example: 14.276 in. - 14.281 in. is converted to (362.611 mm - 362.737 mm) by the IAE metrication program.

            2. The last digit of the minimum is less than 5, but if the minimum is permitted to become 362.61 mm, this will be less than the design minimum in inches and is not permitted. The minimum must become 362.62 mm. The last digit of the maximum is more than 5, but if the maximum is permitted to be 362.74 mm, this will be more than the maximum in inches, which is not permitted. The metric tolerance after round-off is 362.62 mm - 362.73 mm.

      4. Temperatures.

         1. Large tolerance temperatures.

            1. If a Fahrenheit temperature tolerance is +/- 5 deg F or more, round off the Celsius equivalent to the nearest whole degree: 70 deg F - 80 deg F is converted to 21.1 deg C - 26.7 deg C. Round off to 21 deg C - 27 deg C is permitted. 1875 deg F +/- 25 is converted to 1024 deg C +/- 14 after round-off.

         2. Small tolerance temperatures.

            1. If a Fahrenheit temperature tolerance is less than +/- 5 deg F (or for single temperature values), round off the Celsius equivalent to the nearest tenth of a degree is permitted. 72 deg F - 76 deg F is converted to 22.2 deg C - 24.4 deg C (round-off is not necessary).

      5. Physical quantities (ounces, pounds, pints, quarts, etc.).

         1. Quantities are permitted to have the same number of digits to the right of a decimal point in S.I. units as is seen in U.S. units. For example 12 pounds is converted to 5.44 kilograms, and round-off to 5 kilograms is permitted. Ten gallons is converted to 37.85 liters, and round-off to 38 liters is permitted. 2.75 pounds is converted to 1.25 kilograms and no round-off is necessary.

         2. Large-scale dimensions can get the same round-off as quantities. Eight feet (2.44 meters) can get a round-off to 2 meters (accuracy of one or more decimal places is not necessary in the procedure). If the limit is given as 8.0 in., then a metric equivalent of 203.2 mm is applicable.

   3. Mutilation Of Parts

      1. NOTE

         Incorrect control of scrap parts can let these parts back into active part inventories of the aviation community. Misrepresentation of the status of aviation parts and materials (and the practice of making such items apparently serviceable) can have the result that scrap parts are used on certified aircraft.

         If parts are scrap, do a mutilation procedure that causes the parts to become unusable for their initial, intended function, and prevents rework or camouflage by procedures in the subsequent list, or by other procedures, to make such parts apparently serviceable:

         1. Replating.

         2. Shortening and rethreading long bolts.

         3. Welding.

         4. Straightening.

         5. Machining.

         6. Cleaning.

         7. Polishing.

         8. Repainting.

      2. Mutilation can be done by one or more of these actions (but there can be others):

         1. Grinding.

         2. Burning.

         3. Removal of a major lug or other integral feature.

         4. Permanent distortion of parts.

         5. Cutting a hole with a cutting torch or saw.

         6. Melting.

         7. Cutting into small pieces.

         8. Crushing.

         9. Hammer milling.