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Aircraft Engineering: NDT of Outer Starboard Main Plane


The inspection process as specified by the United States of Defence for testing of airplane components is recommended. Initially a preliminary survey of the damage has to be done and then the appropriate inspection process has to be followed (USDF, 28 August 2001).

  1. Preliminary survey of the damage: The component is inspected using techniques such as visual inspection; by touching and by using mirrors, magnifying glasses, borescopes, optical micrometers, camera, and depth gauges.
  2. Selection of Inspection Process. Several factors are considered when choosing the suitable penetrant inspection process. These are as follows: required sensitivity of test, surface condition of test areas, part configuration, testing equipment whether part would be damaged by the dye.

Remaining steps for the process are explained in later sections.

  • Select the penetrant inspection process to be used.
  • Select a part identical to the part to be placed under test.
  • Perform penetrant inspection on the part selected in step 2 in the same manner in which all parts will be inspected.
  • After each inspection process procedure, check the part for damage or adverse effects.
  • If damage occurs, or adverse effects are noted, select an inspection process which will eliminate the problem.
  • Precleaning. The material is carefully cleaned first of water, carbon, engine varnish, dirt paint, oxide, plating, oil or other contaminants, otherwise the penetrant will not be able to get into the flaw and misleading indications may result.

  • Drying. This process is used to assure the evaporation of any water, solvents, or other cleaning solutions, which might be loaded in a crack.
  • Penetrant Application. Penetrant is applied to a part under test in a manner appropriate to the facilities available. Sufficient dwell time should be allowed for optimum penetration. The penetrant is allowed to remain on the surface for a sufficient time to allow penetrant to seep through the defects by capillary action.
  • Dwell (Draining). The part is set aside to drain after the part has been coated with the penetrant. The penetration (draining) time, in minutes, ranges from 5-240 minutes depending on the material of the part and the characteristic of the damage as well as the type of the penetrant (whether water-washable or post-emulsified penetrant). For a post-emulsified penetrant there is usually the additional step of applying the emulsifier after penetration time has elapsed.
  • Emulsifier application, draining and dwelling. This step is optional depending on the type of penetrant used.
  • Developer Application, Draining and Dwell Time. Apply developer to the part. There are several methods but spraying aqueous wet developer is preferred due to its high sensitivity. Wet developers are allowed to drain prior to drying. Developer is applied to the part under test as appropriate to the process being used and the configuration of the part. Developer dwell time will depend on the type of penetrant developer. Sufficient time is allowed for an indication to form, but the penetrant is not allowed to bleed into the developer in such quantities to cause a loss of definition. The part is ready for inspection under appropriate lighting to detect the presence, location, and size of crack.
  • Inspection. The part should be inspected and the crack interpreted. When the surface has been sufficiently developed it will then be examined to see cracks formation.
  • Removal Methods. The developer is removed after inspection by spraying with water or by washing.
  • Repair. The part should be repaired based on the size, depth and nature of the crack. If necessary, repaint the part before returning aircraft to service.

    The paper has presented an overview of NDT and Dye Penetrant Test. The same test has been used on the outer starboard main plane section to detect a suspected crack. The structured procedure specified for the inspection was presented and discussed and the steps to be followed during the testing have been examined.

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