HILL AIR FORCE BASE, Utah -- A team of engineers, inspectors and technicians at Hill Air Force Base are working to create a manual for a Non-Destructive Inspection (NDI) testing program to aid in the regeneration of decommissioned F-4 aircraft that are to be modified into drones.

This NDI program will help find potentially critical degradations in the aircraft flight surfaces before the modifications are completed.

Recently, Terry Watson and others in the QF-4 drone program tested new methods to detect degradations on an RF-4C Phantom II displayed in the Hill Aerospace Museum.

F-4 aircraft to be regenerated have been baking in the Arizona sun for decades at Davis-Monthan AFB and will be inspected and repaired before the drone system is installed.

"Because of the age of the planes, we want to avoid any possible misfortune during flight," Watson said.

Current methods of NDI have proven to be ineffective in detecting the developing degradation in some cases, hence the need to evaluate new detection methods.

The two technologies, under investigation are shearography, and infrared thermography, which can detect failures in composite materials -- or as it's also known -- delamination.

Delamination in the F-4s composite structures happens when the epoxy glue deteriorates which holds together the aluminum honeycomb and skin composite.

The deterioration typically creates an air pocket underneath the skin.

The air pockets can be as small as a fraction of an inch, but when put under the stress of flight (vibrations, changes of temperature and air pressure) these air pockets can grow relatively large, and in some cases rip off the aircraft trailing edge.

Enter Hill's 309th Aircraft Maintenance Group NDI inspectors and technicians.

This group is working on creating a detection protocol for the new technologies.

Shearography uses laser interferometry to detect surface and subsurface anomalies.

Laser interferometry is a methodology which utilizes a characteristic of laser light coherence to measure the change in phase difference from transmission to reception caused by surface anomalies.

A computer generated picture reports any anomalies detected.

IR thermography is similar, but instead of using lasers to detect issues, it uses infrared thermal readings.

In the case of the QF-4 program, Michael Lingbloom, an NDI inspector, said the two technologies will "be another tool in the toolbox of the 309th NDIs."

Once inspected and any necessary repairs and modifications are addressed the QF-4, or drone, will be used for weapons evaluation.

Theâã QF-4s are likened to the use of the BQM-167A -- a smaller drone aircraft also used for weapons evaluation.

The use of non-destructive inspection technologies like shearography and IR thermography can detect delamination with more accuracy than current methods.

Current methods of checking for delamination -- tap tests and ultrasound inspection -- are extremely tedious and prone to misidentification of anomalies.

Shearography and IR thermography demonstrate improvement of detection allowing early repair and mitigation of expensive repair or replacement of delaminated composite parts.