Survey on the Aircraft Structure

INTRODUCTION:

Engineering or Technician during routine inspection / check finds the damage on the upper part of an outer starboard of aircraft main plane, entered the details in the log book and photographed the damage which shows the details of damage which is useful in future. To classify the type and extent of damage, visual inspection was carried out which is not satisfactory and the damage was suspected to be hidden crack. Therefore initial preparation to repair the damaged structure has made by placing the plane in the hanger where all the repair work has to be done. Clean the structure for inspection, care must be taken so that no useful evidence is lost. Manuals like Structural Repair Manual and Aircraft Maintenance Manual are required which provides detailed description of repair work to be done. Alignment and rigging checks are carried out and the values are compared values recorded in aircraft log book which are the original values of aircraft and also compared with structural repair manual which provides standard values and permissible tolerance.

Preliminary survey on the aircraft structure revealed that the damaged structure is suspected to have hidden crack, as visual inspection carried was not satisfactory, colour contrast dye penetrant inspection is advice to carry, before starting NDT examination of structure is carried for any evidence of corrosion on the structure or around bolted joints and also examine for any loose bolts, sheared rivets, distortion or any cracks on the related structures which includes remote positions as well.

NON DESTRUCTIVE TEST PROCEDURE:

Colour Contrast Dye Penetrant Process is referred to one of the oldest and simplest NDT techniques used on Aircraft. This process is applicable to non-ferrous and non-magnetic alloys and is available in solvent clean, water washable, and post-emulsification types. Colour contrast dye penetrant method does not require electricity because the part can be examined under natural lightening condition. Dye penetrant process using field kit is highly portable and preferred method where solvent is used as a cleaner rather than use of water in water washable or post emulsifier.

The procedure for colour contrast dye penetrant using field kit is as follows-

(i) Surface preparation

(ii) Applying Dye penetrant

(iii) Removal of excess penetrant

(iv) Application of Developer

(v) Examine the specimen for defect

(v) Cleaning the surface of specimen

(i) Surface to be tested must be free from dirt, rust, scale, carbon deposits, oil, grease and paint etc. Solvent cleaners are used to all other impurities that could cause false indication of defects. After the part has cleaned the part should be dried with clean and dry cloth or a piece of rag

(ii) The penetrant is applied liberal coating by aerosol cans on the entire surface that is to be inspected. Penetrant must not be allowed to stand longer on the part unless other wise stated. If it is identified that the penetrant is dried the surface should be resprayed with penetrant and cleaned thereafter .Required dwell time is provided for penetrant to penetrate. Dwell time depends upon temperature, type of material, nature of defect, and surface condition. The fatigue and heat cracks requires less dwell time, for seams and forging laps requires more dwell time, in this method dwell time may ranges from 2 to 20 min unless otherwise stated.

(iii) Excess penetrant should be removed by wiping with hand or dirt free cloth, proper care should be taken while removing surplus penetrant, part should not be flushed with liquid cleaners.

(iv) Application of developer is normally done by using aerosol cans. Aerosol cans should be well shaken before use so that developer is uniformly suspended. Fine film of developer should be applied on the part by holding the aerosol cans between certain distance from the surface on the wet part because thick coating of developer may mislead the defect indications.

(v) The part is examined in adequate lighting condition and defect appears as red line under