Maintenance Programs with Current Event

            This week the discussion was to be over maintenance programs and find a recent event dealing with maintenance programs. As I have already discussed the ten elements of a maintenance program in a previous entry, I will focus mainly on the current event. Back in September of 2014, Saudi Arabian Airlines (SAI) underwent their first C check of one of their Airbus A380 aircraft ("Technical Issues," n.d.). This inspection is one of the largest inspection the aircraft can undergo.

            The C check on the A380 is done every other year as a required inspection ("Technical Issues," n.d). Although SAI does not exactly follow FAA standards in regards to AC 120-16F, an attempt will be made to try to relate this large inspection to a few of the elements required for a maintenance program in the United States. The program elements to be related will be the maintenance schedule, required inspection items, and maintenance recordkeeping system (FAA, 2012a). The aircraft that underwent the C check had over 8,000 hours and 1,000 cycles prior to the inspection ("Technical Issues," n.d.).

An effective maintenance program would be fully prepared to conduct this inspection when the time came because of one of the ten required elements is to have a maintenance schedule. It is through this schedule that all planned maintenance is planned to help reduce the down time of an aircraft. During the normal operation of the aircraft, there will be times that discrepancies will be found throughout the year that are not worked off until the aircraft undergoes a major inspection, such as the C check. This is also to reduce down time, and with proper planning, will not impact the length of the inspection being done. The schedule will also ensure proper parts and the appropriate people are in place when the aircraft down undergo the planned inspection. Personnel planning is important, as the C check on this A380 had over 100 trained people to comply with the inspection requirements and also required over 1,600 parts ("Technical Issues," n.d.).

The purpose of conducting the C check is to inspect. The required inspection items should be spelled out so that the inspection is able to flow from one inspection requirement to the next. If the airlines have meet the requirements of another required element, the air carrier maintenance manual, then this should already done.  What should be inspected is generally put together by the airlines with the assistance of maintenance manuals from the OEM.

In the end it is the air carrier responsibility to ensure compliance with OEM inspection requirements, and anything found through the use of yet another of the ten element required of a maintenance program, the CASS. In the event that the airframe or powerplant is new and does not exactly have all the data required to build an effective inspection requirements, AC 121-22C will assist with outlining temporary inspection requirements as the program matures (FAA, 2012b).

The final element is the maintenance recordkeeping system. This is where all the work that was done will be documented. There will also be times that some discrepancies will be found and are not exactly required to be fixed at the time. If this occurs, then proper documentation will ensure that the discrepancies found are documented to be fixed at later time.

To conduct an inspection of this size requires proper planning and preparation. This inspection had over 100 people that worked for 55 days to ensure this aircraft was returned to service and was airworthy ("Technical Issues," n.d.). 55 days is a long time for an aircraft, and without proper scheduling, having inspection requirements laid out correctly, or poor documentation, this aircraft could easily has been down longer. The longer an aircraft is not flying, the more money an airline looses and we all know that the reason the airlines exist are to make money. Below is a time lapsed video of the C check, only in less than 2 minutes.

Federal Aviation Administration. (2012a). Air carrier maintenance programs. Advisory Circular (120-16F)

Federal Aviation Administration. (2012b). Maintenance review boards, maintenance type boards, and OEN/TCH recommended procedures. Advisory Circular (121-22C)

Flightglobal/A380. (n.d.). Technical issues. Retrieved from http://www.flightglobal.com/page/A380-In-Service-Report/Airbus-A380-In-Service-Technical-issues/

Swiss Cheese and its Impact on Aviation

This is not referring to the food that you have to pay handsomely for on a flight from San Diego to New York, but instead to what has become known as the Swiss Cheese Model. This model is fashioned after James Reasons Model of Organizational Accident Causation (Reason, 1995). His model is shown below.

The general concept is that each level, Organization, Workplace, Person, or Defenses, has the potential to contain one or more latent failures that could lead to the outcome. The outcome in this model is an incident or an accident. Typically there is not a single point of failure that causes the outcome and the theory goes that by removing a latent failure, you potentially inhibit an outcome that is not desired. Examples of failures include improper training, lack of proper supervision, and work place culture and climates (Reason, 1995).

            Reasons Model was not aviation specific and was later made into what has become the Swiss Cheese Model. One should quickly see the similarities between the two models. The basic concept is still the same, each hole in the cheese is a latent failure, and when all the slices have holes that line up, an incident or accident is likely to occur.

            So why did I spend some time discussing cheese when the intent of this blog is to discuss aviation inspection and documentation requirements as set forth by the FAA? It wasn’t to make you hungry for a ham and Swiss sandwich, but to try to put the requirements of the FAA into perspective and help people understand that the requirements we have in aviation were ‘written in blood’. Something happened in the past that forced the need for required inspections and proper documentation. Likely something failed and equipment was lost, people were hurt, or someone was killed. Sometimes what is set in place was not enough to prevent an accident and other times the correct procedures were not done. Here I will bring up an accident that did not have enough inspections and incorrect procedures were used on the existing inspections. My hope if that by discussing this accident people will come to appreciate the requirements that are currently out there from the FAA and also understand that inspection requirements evolve and no one can now every failure that could happen.

United Airlines Flight 232 – Failed Inspections

            This particular accident, although not a recent one, is still useful to show why the FAA sets forth the requirements in the various Parts discussed in previous blog entries. The FAA not only sets requirements for the airlines and air carrier, but they also have requirements for the OEMs that supply parts for the aircraft. The NTSB found that inspections were lacking for both the OEM and the airlines in this particular accident, which is why this accident was chosen for this discussion.

Accident Synopsis

            United Airlines was operating a DC-10 under the designation flight 232 on July 18, 1989. The DC-10 has three engines made by General Electric: one under each wing and one on the rear stabilizer. During the flight, the aircraft experienced a failure in the number two engine which is the engine locating on the rear stabilizer. Portions of the first stage fan disk were ejected from the engine casing into the rea of the aircraft. The damage caused by the ejected fan disk caused a complete loss of hydraulic power, to include the backup system. The pilots managed to fly the aircraft to an airport, but without hydraulics, the aircraft touched down with the right wing which caused a summersault like effect. The aircraft broke apart, caught fire, and was subsequently destroyed. Amazingly enough, 185 passengers survived the aircraft accident but 111 never made it home to their families (NTSB, 1989).

            The NTSB would later find two areas of failure that lead up to this accident. The first was the determination that a hard alpha inclusion found just below the surface of the blade formed a crack during the final peening of the disk. This crack ran parallel to the blade which increased the difficulty of finding the defect. Had General Electric performed an ultrasonic or macroetech inspection after the final peening, the defect may have been found and the disk discarded for scrap. The second inspection issue that was found was within United Airlines inspection processes. Multiple sights conducted the inspection of the disks differently from each other with varying results. The third issue was that a documented defect found prior to the final inspection of the suspect disk was already noted but was missed on the last inspection prior to the accident. Between the differences in how the same inspection was done and the fact that a known defect was missed led to recommendations and changes within United Airlines (NTSB, 1989).

Manufacturer Inspections

            Prior to this accident there was already a set standard of inspections that had to be complied with during the manufacturing of titanium billets. One thing that was already noted and was in the process of being changed is how titanium billets were produced. When making titanium they used a double vacuum process of melting down the metals to create the end product. What was found is that the double vacuum process was insufficient in reducing the number of what is called alpha inclusions (NTSB, 1989). The alpha inclusions are created when melting down the metals and are mixed with the gases uses in the melting process. These defects and the number of defects determine whether or not the titanium can be used for specific parts of the engine. For rotating parts, such as the disk that separated in flight 232, the titanium billet must be near flawless. General Electric had already changed their requirements to a triple vacuum process. The disk in flight 232 was the last disk made with the double vacuum process.

            Once the billet is form and inspected the billet will be shipped to the manufacturer which in this case was General Electric. General Electric will also do some inspections to ensure the quality of the product for use in rotating parts of an engine. Once deemed useful for rotating parts, the billet is formed into the part desired. The part is inspected throughout the process to ensure defects weren’t added during the machining process. Just prior to the final peening of the disks, a macroetech and ultrasonic inspection is done. Once the final machining is done there are no more NDIs done on the finalized part. Conducting the macroetech and ultrasonic inspections after the final machining may have located the crack and resulting in the removal of the disk from service.

United Airlines Inspections

            During the investigation in the inspection processes of United Airlines, the NTSB found that the suspect disk was inspected multiple times with several defects within limits on the suspect disk. The last time the disk was removed and inspected, previously noted defects were not found by the inspection team (NTSB, 1989). This lead the NTSB to look deeper into how the disks were inspected. During visits to multiple facilities used to inspect the disks, they noted that no two did the inspection the same. Inspections should be standardized within the airlines to prevent confusion or the chance that inspection requirements may be missed. What was eventually determined is that the last inspection was not done in compliance with OEM data. Although the defect that led to the accident may still not have been found, the process was still flawed and lead to the possibility of missed defects conducted at later times. What was the current inspection methods were found to be lacking and eventually lead better inspection methods for finding cracks.

Conclusion

            The problem here started with inspections from the manufacture of the engine. Had the process been looked at closely prior to this accident perhaps someone would have suggested more inspections of the parts after the final machining and peening of the blades. Better inspections within the airlines may have also been able to detect the crack and remove it from service prior to catastrophic failure and death of people on an aircraft. Fortunately, with the documentation requirements at the time of the accident, they were able to identify issues with the lot of billets and disk made from the same titanium. Inspections were issued because of the accident which lead to the removal of the other five disks made from the same lot. Improvements were made within United Airlines to also try to mitigate future incidents or accidents.

            So going full circle with the starting discussion of latent failures and Swiss cheese, many slices existed and at any time could have prevented this accident. The double vacuum had already been deemed insufficient in removing defects, but this last lot was still used. General Electric could have been better with inspections prior to releasing parts for use in an aircraft. Finally United Airlines could have trained better for inspections of engine rotating parts and standardized their process better to ensure compliance and consistency in the inspections conducted. More slices could likely be identified if you dig deep enough but from an inspection stand point these failures should have been found long before 111 people died.   

References

National Transportation Safety Board. (1989). United airlines flight 232. Aircraft Accident Report (NTSB/AAR-90/06 PB90-910406).

Reason, J. (1995). A systems approach to organizational error. Retrieved from http://www.tandfonline.com/doi/abs/10.1080/00140139508925221#.VGjwNPnF_cw

Maintenance Program Requirements

            Ten elements of a maintenance program were mentioned during the discussion of the CASS, the other elements will now be discussed in part. One of the remaining elements is the air carrier’s airworthiness responsibility. The airworthiness responsibility simply outlines that the requirements to meet all ten elements of a maintenance program are the direct responsibility of the certificate holder and/or owner of the aircraft. Depending on how the aircraft is certificated will determine the specific Part, 121 or 135, that will direct the specific maintenance functions required for continued airworthiness for that aircraft. Regardless of operation under Part 121 or 135, Part 43 must also be followed for the maintenance, preventative maintenance, rebuilding, and alterations of aircraft along with their specifics outlines in either Part 121 or 135.

            The air carrier maintenance program has three overall objectives. The first objectives is to ensure that all aircraft released for service do in fact meet airworthiness requirements. Objective number two requires that all maintenance done on an aircraft are done in accordance with the maintenance manuals. The final objective is that the air carrier provide competent personnel and appropriate facilities and equipment to perform the maintenance correctly (FAA, 2012). To achieve these objectives on the maintenance side is where the other eight elements required for a maintenance program come in. The eight elements are the air carrier maintenance manual, air carrier maintenance organization, accomplishment and approval of maintenance and alterations, maintenance schedule, required inspection items, maintenance recordkeeping system, maintenance providers, and personnel training. Each will briefly be discussed below.

Ø  Air Carrier Maintenance Manual

o   Must be easily revisable and readily available to personnel for use

o   Needs to be standardized and usable by third parties in the event of contracted use

o   Contains OEM data, but written by the air carrier – cannot use OEM publications

Ø  Air Carrier Maintenance Organization

o   Part 121 and Part 135 require a Director of Maintenance and a Chief Inspector (or equivalent position)

o   Structure is required but is necessarily broad for the wide range of air carrier sizes

§  Recommends accountable manager – monitors and manages both maintenance and inspections functions

§  Clear authority, to include delegated responsibility, needs to be clear

o   Maintenance and Inspection need to be separated

Ø  Accomplishment and Approval of Maintenance and Alterations

o   Must meet the requirements of respective Parts

o   Major Repairs and Alterations must be done in accordance with FAA

o   Post maintenance actions require aircraft logbook entries and approval for RTS

o   Maintenance can be scheduled and unscheduled

Ø  Maintenance Schedule

o   Objective is to do the correct task at the correct interval

o   Schedule should contain the following:

§  What the task is – examples include service bulletins, special inspections, lubrication or servicing

§  How – how will the task be performed, does it require special tooling, specific facilities, special personnel

§  When – what is the time table for the inspection. This includes when to perform the task (time window), how long the task should take, and when to expect it to RTS

Ø  Required Inspection Items (RII)

o   Certain tasks are required to be considered RIIs. The expectation is to maintain a list of what is an RII.

o   Is a large part of maintenance schedule and maintenance manuals

§  Manual must include a list of persons for any required inspections

§  RII requirements must be clearly identified

§  Standards and limitations must be set

§  Manual must contain all procedures for the RII

Ø  Maintenance Recordkeeping System

o   The purpose of records is proof of work done to keep an aircraft airworthy

o   Part 43 contains the basic guidelines to be used for all recordkeeping

o   Must have copies of all records

o   Some records require reporting to the FAA, such as major maintenance and alterations, even when done in accordance with the OEM data

Ø  Maintenance Providers

o   Although done by a third party (leasing agent, outsourced, contracted), the final responsibility relies on the air carrier to ensure compliance with all requirements

§  This includes recordkeeping

Ø  Personnel Training

o   The certificate holder is responsible for ensuring the proper training of all maintainers that are to be used for the aircraft operating under them. Some of the training required are:

§  Initial training

§  Recurring training

§  Specialized training

§  Maintenance provider training

§  Competency-based training

Federal Aviation Administration. (November 15, 2012). Air carrier maintenance programs. Advisory Circular (120-16F). 

Continuing Airworthiness

        Having an aircraft that meets all Airworthiness Directives is not a difficult task to accomplish with the proper plan and supervision. As mentioned in the previous blog, maintenance is a large part of how an air carrier gets an aircraft to meet the standards set forth to have an aircraft ready to fly in accordance with all the standards and directives. But how does an air carrier know what maintenance to perform, when to perform various inspections, how is the work documented, and who verifies that everything required is done?

            Both the FAA and EASA again have similar goals towards airworthiness, but the methods and references used differ greatly between the two. The focus is on producing a quality product in the cheapest and safest way possible without endangering the lives of the people on board the aircraft. Both the FAA and the EASA will be discussed briefly.

The FAA directs the requirement to maintain ten elements of a maintenance program. One of those ten elements is called Continuing Analysis and Surveillance System (CASS) and is outlined in Advisory Circular (AC) number 120-79A. Through this system, the air carrier is able to augment and improve how the carrier decides when to perform maintenance, schedule inspections, ensure proper documentation of work performed, look for trends, and ensure continued airworthiness. Directly from AC 120-79A, the high level purpose of the CASS is to “reduce or eliminate the likelihood of your aircraft being approved for return to service (RTS) when it is not airworthy through the continuous, system safety-based, closed-loop cycle of surveillance, investigation, data collection, analysis, corrective action, monitoring, and feedback (FAA, 2013).”

The EASA sets forth the requirements for continuing airworthiness through Continuing Airworthiness Requirements – Part M. Despite being a large document, the requirements are not as straight forward and have a tendency to be a bit vague. The requirements do set forth some similar ideas and methods used in the FAA, such as setting up maintenance standards, continuing airworthiness guidelines, maintenance management and organization, and sets up guidelines for setting up competent authorities. The competent authorities are used for inspection purposes. EASA focuses a bit more with meeting inspection requirements and relies on the competent authority to verify everything is done correctly, documented, and that the aircraft is in fact airworthy.

Federal Aviation Administration. (May 17, 2013). Developing and implementing an air carrier continuing analysis surveillance system. Advisory Circular (120-79A).