NDI of Fighter Aircraft

Mr. Regler reviewed NDT work done as part of basic maintenance over the course of 110 working days which included 220 hrs. of NDT work. The goal of the NDT work is the detection of defects which may classified in groups as follows:

• Fatique
  cracks, delamination
• Environment
  corrosion, heat, erosion
• Force
  notches, bumps, weak points

In addition, the detection of foreign objects in the air intake areas is a part of NDT. The NDT personnel must meet the following standards:

• DIN 65450
• ENpr 4179, the standard draft should already be out, but it's late
• Mil-STD-410E
• Lyndon B. Johnson Space Center
• Learjet approval

Some NDT application examples are introduced:

On Tornados aircraft a corrosion problem occurred around titanium rivets on aluminum structures; this phenomenon is observed after about 10 years of use. Quantitative determination of defects size and remaining wall thickness at corrosion is important. A replacement of the part is very expensive so NDT results are required for risk management.

A system from Stavely (Nortec 30 Eddyscan) can do hole inspection without disassembling. The principle works with a Hall effect sensor and an eddy current coil. Inspection is possible at a depth of 12-15 mm; only the EC rotating probes with removed bolts delivers better results.

Heat spots damages are inspected with conductivity tests and in many cases an additional hardness test is performed. That is not possible with titanium components where the tarnish method (discoloration) is used.

X-ray is used for welding tests at aerospace components in a clean room. Titanium tubes of 5 to 8 mm diameter with 0.3 to 0.8 mm wall thickness are tested.

The Learjet is tested inside on crack and corrosion after almost all components are disassembled. It is difficult to find a working position for the X-ray source in this small area full of cables.

90% of the Eurofighter's CFK composite parts are inspected with ultrasonic testing. A main task of the inspection is the detection of impact damage on its sensitive surface which is not highly visible on the surface, but damaging to the inner structure. Inspection classes are A: 3x3 mm, B: 6x6 mm and C: 9x9 mm, usually class B is specified for ultrasonic testing.
UT with dry coupling using roller probes is also applied for inspection of corrosion and delamination of the honeycomb structures.

A simple but effective visible inspection is performed with glasses and prism on windscreens.

When asked if developing methods like lamb waves or shearography are already regularly applied, Mr. Regler answered "not yet but we are investigating this".