A bare metal inspection is commonly abbreviated to BMI and is commonly used to refer to the inspection of a metallic fuselage that is stripped of paint.
It is not a mandatory task to repaint aircraft, the paint is a protective layer and while it must be maintained, it can be repaired or “touched up” as required. With this in mind then we can determine that the fuselage is not in this condition regularly.
For some end-of-lease requirements, part of this is to present the aircraft in a white livery. It might not always require a repaint of everything and might be limited only to the fuselage or only covering logo for example.
Why this inspection is so important is based on the unique viewpoint you have of the aircraft surfaces and fuselage. The dent & buckle (D&B)can be referenced as you walk around, and the BMI is a chance to extend that and fully document the status of the aircraft before becoming hidden under paint. You can view hidden or hard-to-see damage on the aircraft around the joints such as lap joints where the skin overlaps at a joint.
Any queries or new damages can be noted and a photo of the damage and further back to accompany and show the area is ideal. It is advisable to bring these items to awareness as soon as you can via the relevant path. For example, as a receiving representative you might have an onsite representative for the lessor and so you can highlight these to the rep and enter them on an open item list.
If you work on behalf of the airline then it might be important to make the part 145 and part CAMO aware as the areas may well be protected with speed tape to allow the paint input to progress and rectification and evaluation can occur them at a later stage.
Common examples of additional damage can include lightening strikes on skin edges or fasteners, scratches in the skin or upper clad layer, rivet heads sanded flush, scribe lines (where a knife or sharp edged object has been used along an edge of skin, decal or around an object typically and damaged the skin).
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