Technical Review of Fluorescent Penetrant Inspection Process

NDT.net - January 2002, Vol. 7 No.02

TECHNICAL REVIEW OF FLUORESCENT PENETRANT INSPECTION PROCESS

CONDUCTED BY THE FEDERAL AVIATION ADMINISTRATION
The Airport and Aircraft Safety Research and Development Division (AAR-400)
JULY 14, 2000
This is a publicly available report extracted from the Summary Report,
Technical Review of Penetrant Inspection Process, dated March 28, 1998.

I. EXECUTIVE SUMMARY

The on-site facility review core Team generally consisted of the Chief Scientist & Technical Advisor, Nondestructive Evaluation, an Aerospace Engineer from the Engine Certification Office, Aircraft Certification Service, and an Aviation Safety Inspector from the Boston Aircraft Evaluation Group, Flight Standards Service. Additionally, each on-site visit was enhanced through the addition of Aviation Safety Inspectors from the Flight Standards Service with specific facility oversight responsibility.
The Team concentrated on the following three major areas during all on-site visits:
1. Qualification of Personnel
2. Cleaning and Handling
3. FPI Process
This report summarizes the results of the seven FPI reviews.

The facilities responded positively to the observations and recommendations made by the Review Team and implemented the necessary changes. Each cognizant Flight Standards Office through its own follow-on action has provided a report documenting the final corrective actions taken by the facilities.

II. BACKGROUND SUMMARY

An investigation revealed that during the takeoff the fan hub separated into two sections approximately 120 and 240 degrees of the circumference with fan and/or engine debris penetrating the aft cabin area, resulting in two fatalities and one serious injury. The fractured fan hub, Part Number 5000501-01, Serial Number R32971, was last inspected in December 1995, after accumulating 12,693 flight cycles. The fan hub failed at 13,835 cycles (1,142 cycles since last inspection). The published life limit of this fan hub is currently 20,000 cycles.

The investigation also revealed the fan hub failure resulted from a fatigue crack that originated in a tie bolt hole. The fatigue crack initiated from mechanical surface damage produced during the machining of the tie bolt holes at manufacture, and propagated in a low cycle fatigue mode due to normal engine start-stop cycles. The manufacturing records indicated that a surface anomaly was observed in a tie bolt hole during a Blue Etch Anodize inspection. The anomaly was dispositioned to be acceptable by the inspection standards in effect at that time.

The National Transportation Safety Board (NTSB) performed a metallurgical examination. Results suggest a 1.36 inch crack in total surface length was present at the last Fluorescent Penetrant Inspection (FPI). The crack extended 0.46 inches on the aft end face of the hub and continued along the wall of a tie bolt hole approximately 0.9 inches. Published reliability data from the Nondestructive Testing Information Analysis Center indicates that a crack of this size should be detectable with a probability of detection and confidence level both exceeding 95 percent.

On July 29, 1996, the NTSB issued Safety Recommendation A-96-77 which recommended the Federal Aviation Administration (FAA) review and revise, in conjunction with the engine manufacturer and air carriers, the procedures, training that includes the syllabi and visual aids, and supervision provided to inspectors for performing FPI and other nondestructive testing of high energy rotating engine components, with particular emphasis on the JT8D-200 series tie rod and stress redistribution holes.

The Manager, Engine & Propeller Directorate, formed a FPI Process Technical Review Team on August 6, 1996, to review the FPI process and operations at Delta Air Lines, Inc., in support of the failure investigation.

In an effort to determine whether systemic problems exist in the available FPI guidance material or its implementation, and to develop corrective actions as necessary, the Manager, Engine & Propeller Directorate, reformed the FPI Process Technical Review Team on September 12, 1996, to examine six additional facilities which perform FPI of high energy rotating engine components and to provide their observations and recommendations to the Engine & Propeller Directorate.

III. DISCUSSION

1. Qualification of Personnel

2. Cleaning and Handling

3. FPI Process

The Team completed a total of seven individual FPI reports based on these reviews, which contain the observations and recommendations in the three major areas noted above. This report is a compilation of all seven reports, providing the Teams' overall conclusions and recommendations to the Manager, Engine & Propeller Directorate. The Team was not specifically tasked to document positive observations, therefore, the reports address observed deficiencies only.

The FAA's intent was to sample FPI facilities that process a large quantity of critical rotating engine components. The types of facilities sampled included major air carrier maintenance, engine manufacturer repair, and independent repair facilities. The distribution for the seven facilities sampled is shown in Figure 1.

Fig 1: Distribution of FPI Facilities

A total of 157 observations were documented by Team members during the seven FPI on-site facility reviews. Figure 2 provides the distribution of the Teams' observations for the three major review areas.

Fig 2: Major Review Areas

This report addresses the three major review areas in Figure 2, and cites the Team's objective and the outcome of the reviews. All observations in each major review area have been condensed into sub-elements to promote a clearer understanding of the observed deficiencies.

A. Qualification of Personnel

Objective: Inspections are performed by qualified personnel.

A total of 44 Team observations were made in the area of inspector qualification. The Qualification of Personnel review focused on a comparison between the guidance material used by the facility and the industry guidance. The Team determined whether the facility was following their own guidance. Those observations have been condensed into the following four generic areas: Documentation/Manuals, Certification/Recurrent Training, Tracking Systems, and an area called Other, as shown in Figure 3.

The FPI inspectors overall, appeared to be responsible individuals who are motivated to do a good job. At some of facilities this was evident in spite of poor organizational oversight of the inspection operation. In most of the facilities, formal recurrent training did not exist. This was evident by non-compliance to procedures, poor documentation and in some cases not having the appropriate qualification requirements to accomplish work assignments.

Documentation/Manuals: In parallel with training and certification, is the need to document the results for historical purposes and provide evidence of compliance to the procedures. Several observations were made where the procedures or manuals were not revised to the latest standards, or were in need of revision to clarify the intent of the instructions provided.

Fig 3: Qualification of Personnel

Certification/Recurrent Training: These observations ranged from non-performance of required certifications or recurrent training of inspection personnel, to the facility not having the appropriate certification requirements. Several instances of non-compliance to the recurrent visual testing was of particular concern to the Team.

Tracking Systems: The observations made in this category clearly indicated a need to revise or implement tracking systems. This would provide proper monitoring of inspector qualifications and provide a mechanism for identifying when recurrent training is required.

Other: This category captures all remaining observations, and has the third largest number of observations. These observations range from the need to establish and perform audits of training systems, to revising the forms used for record keeping.

The inspector's practical experience is to find numerous indications in the items he/she inspects. In some cases, indication finds are daily. However, the bulk of those indications found are not on critical rotating components. Indication finds on critical rotating components are very rare. Since FPI lines do not discriminate between critical and non-critical components, the inspection practices established by inspectors will not either. Less than optimal inspection techniques may be adequate in finding indications on non-critical components, but will give the inspector a false sense of expectation in finding indications on critical rotating components. The importance of training, certification and currency through recurrent training in a timely manner can only be emphasized. A general response by inspector's when it's pointed out that he/she is using less than optimal techniques is "I'm still finding cracks". The concern is, are we missing any cracks?

B. Cleaning and Handling

Objective: Components have been properly handled and cleaned for inspection.

A total of 59 observations were made in the area of Cleaning and Handling. The cleaning review focused on a comparison between the guidance material used by the facility and the industry guidance. The Team determined whether the facility was following its own guidance material. The facility was also evaluated on what was considered to be good practice. The cleaning observations have been condensed into the following five generic areas: Process/Procedure, Calibration, Oils, Media Blast and Other as shown in Figure 4.

Fig 4: Cleaning

Process/Procedure: These observations ranged from non-compliance with requirements, to the need for revising and updating manuals and processes to ensure that cleaning methods have been substantiated by approved data. Several observations of current cleaning practices led to the Team's recommendation to discontinue the practice until the process could adequately be accomplished.

Calibration: The Team noted several observations where the review of standard practices was required to ensure that the operating pressures and temperatures were correct, and the need to revise the manuals to include specific operation procedures for gauges. The Team recommended the use of electric timers as a reasonable expected practice in place of personal wrist watches or wall clocks.

Oils: Several observations on the inappropriate use of penetrating oils for engine disassembly were noted. In some cases, penetrating oils were used which were not on an approved list. Penetrating oils should be used sparingly to prevent the possibility of residual oil remaining in a crack if not cleaned properly.

Media Blast: The majority of Team observations were on the use of media blast cleaning processes. The facilities were required to review the recommended media blast guidance material to ensure the use of proper types of media, and to set operating pressures to the recommended levels. Other: These observations were applicable to the implementation of qualified personnel to perform cleaning processes, and the use of placards on tanks for identification of temperature ranges and contents.

C. Fluorescent Penetrant Inspection (FPI) Process

Objective: Perform inspections that detect cracks.

A total of 54 observations were made in the area of FPI Process. The FPI Process review focused on a comparison between the guidance material used by the facility and the industry guidance. The Team determined whether the facility was following its own guidance material. The facility was also evaluated on what was considered good practice. The FPI Process observations have been condensed into the following four generic areas: Procedures, Handling, TAM Panels (an FPI verification tool), and Other as shown in Figure 5.

Fig 5: Fluorescent Penetrant Inspection Process

Procedures: These observations ranged from non-compliance with requirements, to the need for revising and updating manuals and processes. In some cases, improvement and clarification of guidance material was needed to bring the guidance material up to their most current versions. Of particular concern was the guidance material for the use and maintenance of TAM panels.

Handling: The noted observations were to review shop practices, and to revise and implement shop practices to preclude metal-to-metal contact between the part and handling fixtures.

TAM Panels: Several observations were relative to the improper use of TAM panels. The Team recommended FPI personnel receive refresher training in the use of TAM panels. Of concern was the disconnect in the cleaning, storage, and the overall process for the use of TAM panels.

Other: These observations were relative to training in the handling, processing, and process control parameters of the FPI process. This included the use of timers, labeling of tanks, and use of fixtures.

IV. CONCLUSIONS

General:

The observations documented in this report indicate poor quality assurance practices at most of the reviewed FPI facilities. Extensive changes in the areas addressed by the Team have occurred at a number of the facilities following the Team's review.

Qualification of Personnel

The certification and recurrent training of inspection personnel were either poorly structured or practically non-existent. The documentation and tracking of inspector qualification and training was incomplete. Tracking systems lacked the capability of providing notification when inspector recurrent training was required. Procedures and manuals were not revised to the latest standards, or were in need of revision to clarify the intent of the instructions. Missing from the qualification of FPI personnel was experience and validation of performance on actual engine hardware with real indications.

Cleaning and Handling

There seemed to be a pervasive lack of concern on the part of Level III's and managers of FPI organizations that items, before reaching the inspection area, had been properly prepared for an inspection. The high rate of return of items going back for cleaning was treated as a conflict issue between shops rather than an indication of deficiencies in the cleaning process.

There was little sensitivity of the cleaning organizations as to the next destination of the parts. The cleaners simply "cleaned". Parts going to the FPI line were not treated any differently from those going to other destinations. There was a lack of sensitivity to the issue that parts had to be clean enough for inspection.

Unapproved penetrating oils were present, and utilized for engine disassembly in most of the facilities. There was little concern on the part of FPI personnel regarding penetrating oils and the negative impact they may have on the adequacy of pre-cleaning.

FPI Process

There are acceptable procedures and guidance in place for qualified inspectors to perform the FPI process. There was no single guidance document that was utilized by the facilities visited. Each of the engine Original Equipment Manufacturer's (OEM's) guidance is different. OEM guidance also differs from the current guidance in place at some of the facilities. There was some re-labeling of the procedure steps at the facilities. There were some facilities that generated their own generic procedures because they processed more than one OEM's engines. Improvements in the guidance materials should be made to improve and clarify requirements, and bring procedures up to their latest revision. A single, complete, easy to follow, stand-alone guidance document is needed to ensure that proper utilization, consistent and uniform procedures, and easily auditable instructions are achieved.

An observation applicable to most of the facilities was the improper use of TAM panels in the areas of: interpretation of guidance material, maintenance and cleaning procedures, and overall utilization.

V. RECOMMENDATIONS

Support the adoption of a single document for FPI process guidance and work with the Engine Manufacturers, end users, and providers of FPI materials to disseminate guidance information to all entities. A reasonable candidate for an industry standard is SAE 2647A, soon to be superseded by SAE 2647B, "Fluorescent Penetrant Inspection, Aircraft and Engine Component Maintenance".

Conduct Research and Development Programs to:

Assist in the implementation and maintenance of best practices for FPI for use by the aviation industry. Includes the performance of engineering studies to evaluate the critical parameters in the pre-cleaning and drying steps before the FPI process.
Generate and assist in the implementation of a generic performance verification sample kit so that the air carriers and repair stations can assess their capability relative to that performance verification kit.
Evaluate the need for an universal FPI kit that would aid in inspecting difficult areas (i.e., cavities in hardware), and develop common tooling.
In cooperation with OEM's, provide FPI training materials for use by the airlines and overhaul and repair organizations.

Communicate to the Flight Standards Service the need to assure that only qualified personnel are engaged in the performance of FPI.

Support the implementation of documented training for cleaning personnel in the practices and procedures they employ. Especially for those items which will subsequently be inspected by FPI. For the performance of FPI, a number of acceptable consensus industry/military guidance documents exist for the qualification of personnel. Similar guidance for cleaning personnel does not appear to be available. The Engine & Propeller Directorate should also support the establishment of a guidance standard by an industry group such as ATA.

The Engine & Propeller Directorate should request from the OEM's, data that supports their guidance on cleaning, plastic media blast, and drying of parts prior to the FPI process; and the impact, if any, the above guidance material may have on the adequate detectability of cracks in critical rotating components.