Documentation for Aging Aircraft Maintenance

An aging aircraft is capable of retaining its airworthiness from an evaluation of the maintenance program that the FAA conducts. After the airplanes 14th year of service (the calendar time elapsed since the FAA issued an airplane its first U.S. or first foreign airworthiness certificate), certain airplanes must undergo inspections and records reviews by the agency who administered the certificate. This action ensures the maintenance of the airplanes' age-sensitive parts and components has been adequate and timely

(U.S. Department of Transportation, 2009). To ensure that this is being conducted properly the FAA takes sample tasks and records for the airplane and then continues to monitor the air carriers' maintenance program.

When the Advisory Circular 120-84 was put into place on Jan 15 2009 it was assumed that airplanes over 24 years would have inspections done during the next available check and then airplanes 14 years or older had a more extensive period of time to comply with the FAA's request. This was to better accommodate the work load of the FAA personnel doing the inspections of the maintenance records. The airline was also able to request an extension of 90 days if there were unforeseen circumstances that would prevent the FAA from being able to conduct the inspection on the scheduled date.

After the initial inspection then the air carrier is expected to schedule with the FAA 60 days prior to the aircraft going into it's next scheduled shop visit where a repeat inspection is expected. The interval is expected to be every seven years which generally means every Heavy Maintenance Visit (either 4C or a "D" check).

During a records review the following information must be made available to ensure compliance

(U.S. Department of Transportation, 2009):

• Total years in service of the airplane;
• Total time in service of the airframe;
• Total flight cycles of the airframe (not required under Part 135.422(d));
• Date of the last inspection and records review required by the Aging Airplane Safety Rule;
• Current status of life-limited parts of the airframe;
• Time since the last overhaul of all structural components required to be overhauled on a specific time basis;
• Current inspection status of the airplane, including the time since the last inspection required by the inspection program under which the airplane is maintained;
• Current status of applicable Airworthiness Directives (AD), including the date and method of compliance (and if the AD involves recurring action, the time and date when this action is required);
• A list of major structural alterations; and
• A report of major structural repairs and current inspection status for those repairs.

This does not include the fact that the Aging Airplane Safety Rule requires certain airplanes from operating unless damage-tolerance-based inspection and procedures are included in the maintenance or inspection program for each airplane in accordance with a specified schedule. The operator is also expected to asses adverse effects of any repairs or alteration on fatigue-critical structures. There are no specifics mentioned in the AC that tell when these inspections are suppose to occur.

Once the aircraft has been determined to be in compliance with all the requirements for an aging aircraft then it is issues a "Result of Aging Airplane Safety Inspection" document to be maintained with the other records to indicate its compliance.

Example of Results Document

U.S. Department of Transportation. (2009, January 15). Aging Aircraft Inspections and Records Reviews. Advisory Circular. Washington, DC, United States of America: Federal Aviation Administration.

Flow Chart to Determine Aging Aircraft Applicability

The FAA had recognized the dangers of aging aircraft and had published the Aging Airplane Safety Interim Final Rule on December 6, 2002. On February 2, 2005, the FAA published the Aging Airplane Safety Final Rule (U.S. Department of Transportation, 2009).

The final rule specifies the following (U.S. Department of Transportation, 2009):

• Mandatory aging airplane inspections for certain airplanes according to their years in service
• Damage-tolerance-based inspections and procedures to be included in the maintenance programs of certain airplanes
• Operation of these airplanes after specified deadlines will cease unless the maintenance programs under which th eairplanes are maintained include damage-tolerance-based inspections and procedures.

In order to determine the applicability the operator can use the following charts to determine if their aircraft qualify for an aging aircraft.

Decision Logic - Initial Inspections and Records Review Due Date

Decsion Logic - Applicabiltiy of Inspections and Records Review

U.S. Department of Transportation. (2009, January 15). Aging Aircraft Inspections and Records Reviews. Advisory Circular. Washington, DC, United States of America: Federal Aviation Administration.

Maintenance Tasks

Aircraft should be maintained on a regular basis based on manufacturer intervals or their own maintenance program. The maintenance programs are submitted to the appropriate regulatory authority for approval. Operator maintenance programs have to follow a general baseline of the manufacturer’s maintenance program but based on experience with the aircraft can have the life limits and intervals extended.

How does maintenance affect the age of an aircraft?

As an aircraft ages the intervals of the maintenance checks known as "C Checks" merge to create even heavier maintenance visits. These visits end up costing more money than initial checks and more non-routines are generated due to the age of the aircraft. Here is an example of a maintenance program and how the age produces a heavier check.

Note: This is a made up example based on the standard 18 month interval mentioned in the Aviation Maintenance Management book written by Kinnick and is by no means meant to reflect any specific airline maintenance program.

Notice how the third interval of the 4C Check/HMV Check matches with the 3C, 2C, and 1C Checks. At 216 months the aircraft would be 18 years old. By now an operator may start thinking about replacing their aircraft before this maintenance visit happens because of how much it costs to actually conduct this maintenance.

No matter how good the maintenance being conducted is the fact is the aircraft is still aging and certain other tasks start populating because of that. The aircraft bins may need to be painted, the light covers yellow, seat cushions have to be replaced, and this doesn't cover the standard hard time components that life span may be coming due. Some hard time components such as slides have to be sent out for overhaul at about 5 to 7 years and depending on the age of the slide will have to be sent out every year to two years for overhaul. At this point it may be more cost effective to just purchase all new slides instead of overhaul this is no different then determining if continued use of an aging aircraft is worth the cost of the maintenance.

Performing continued maintenance is very important for actually reaching the expected economic life of an aircraft as well. When maintenance isn't performed and the aircraft sits on a ramp or in a storage area then the parts tend to start to corrode a little easier because lubricant may not be applied as often as it would normally. Airplanes that rest too long can become home to animals which can damage wiring and insulation in order to make their nests causing additional maintenance tasks in the future should the aircraft ever be attempted to be reactivated.

Proper maintenance during C Checks is also important. Human factors is a huge issue when it comes to maintenance and many times when an aircraft ends up having an issue the maintenance task performed was done so incorrectly. This was part of the reason why the Aloha flight had the issue. Aloha had been operating the aircraft past its economic life which was one of the reasons why the top part of the fuselage separated from the bottom half. Another reasons was due to improper maintenance procedures. When the airline was under investigation it was determined multiple other airplanes were showing the same cracks and issues as the accident aircraft. This is why proper maintenance and an ultimate life are important when dealing with aircraft.

Conclusion

Over the course of this brief blog post the author has spoken about the importance of continued maintenance on the aircraft. By doing continued maintenance there is a reduced chance of animals nesting or corrosion happening on the aircraft. When performing correct maintenance the life of the aircraft can be expected to meet the ultimate life as what is suggested by the maintenance manufacturer. Overall though it is the responsibility of the airline operating the aircraft to ensure that a replacement plan is in place once the aircraft starts nearing its end of life and to make sure that maintenance is performed in a timely manner to keep the aircraft airworthy.

Quality Assurance

Some of the issues that have come up in regards to aging aircraft is how they are maintained. Quality assurance personnel are responsible for making sure that maintenance cards are carried out in a timely and accurate manner to make sure the aircraft keeps it's airworthiness capabilities. Maintenance planning documents are prepared by the manufacturer, can be customized by the operator, and reviewed by the regulatory authority. The manufacturer is also responsible for determining an ultimate life to assigned to their aircraft or engine model in order to ensure that the aircraft or engine does not exceed limits and becomes a hazard.

Airframe life is important to determine because there is constant stress being applied to the airframe as it pressurizes and depressurizes during a single cycle. Think of the airframe as a rubber band, under continued stretching and release eventually the elasticity weakens and the rubber band breaks. This is the same as what can happen to an airframe as the elasticity of the metal is weakened and eventually becomes brittle and breaks. Under the same rules it's important that when the aircraft is part of a fleet that it is used on a regular basis because exposure to the elements and constant sitting also reduces the properties of the metal.

Most other parts of a particular aircraft have life limits much like that of the airframe. Once a life limit is reached the part must no longer be used. This is true for landing gear and engines. In general for landing gear there is a list of limited parts with an expected life span in cycles and months. For engines the expected life span is expressed in flight cycles or flight hours depending on the part. The manufacturer is responsible for determining these life limits. Keep in mind that when a new engine model is created the life limit may be far lower than the expected ultimate life. Engines are generally utilized differently per airframe model that it is attached to and how the operator uses the aircraft. Aloha air utilized their 737's as "puddle jumper" airplanes and increased the stress put on the engines by using shorter flight hours and more cycles per flight hour. This is different then Alaska air who may be running an engine with one flight cycle per every 4 flight hours.

It is quality assurances responsibility to ensure that the life limits for all parts on the airplane are not exceeded. You wouldn't want an engine coming apart because of a life limited part that has exceeded its recommended life just as you wouldn't want to open a life jacket and realize that the material is degraded because it has exceeded it's expected life as well. Operators have a way to track and monitor this information and do so on a regular basis to ensure that the aircraft is safe for flight. It is quality assurances responsibility to ensure that the maintenance on all components of an aircraft is completed. Aged aircraft just tend to have more frequent maintenance tasks that have to be performed.

Requirements for a Maintenance Program

Aircraft Aging has many exterior factors instead of just the initial age of the aircraft. Some of the exterior factors can be how the aircraft is maintained and where it is stored. When an aircraft is improperly stored and maintained the aircraft tends to "age" more rapidly or in a sense reach it's life limit far sooner than manufacturers recommendation. Some areas of aircraft are more likely to have corrosion happen then others based on the materials that are exposed to the elements. Examples of these areas are (Aviation Safety Bureau, 2010):

• The battery compartments
• Bilge areas
• Bulkheads
• Wheel wells and landing gear
• Water entrapment areas
• Wing flap and spoiler recesses
• Areas hit by exhaust steam
• Cooling air vents
  
  

In order to maintain the aircraft in good working condition there are various ways in order to assist in preventing such corrosion to happen. One of the major reasons is to follow recommended intervals for maintenance and to have a maintenance facility capable of handling all necessary repairs. When an aircraft is in storage it is important to cover all open areas to prevent animals and moisture from entering these areas and causing excess damage. Also storage in a warm arid place assists in preventing damage.

Where not to store an aircraft:

Old hangers that have not been maintained properly. Moisture can easily be trapped in these hangers causing ideal conditions for corrosion to exist. There may even be heath issues associated with lead paint or asbestos in hangers such as these.

Near salt water. Salt water easily starts to cause corrosion not just on the airframe but also inside the engine. It is recommended that after being near salt water that an engine wash and an aircraft cleaning are done.

Corrosion Prevention and Control:

Due to the amount of damage that is caused by corrosion all operators of aircraft are expected to have a corrosion prevention and control program (CPCP). According to the Federal Aviation Administration (1993) the Baseline Program for CPCP recognizes three levels of corrosion that are used to assess effectiveness:

• Level 1 Corrosion found during the accomplishment of the numbered Corrosion Task indicates an effective program.
• Level 2 Corrosion indicates that program adjustments are necessary.
• Level 3 Corrosion is an urgent airworthiness concern requiring expeditious action on the part of the operator to project its entire model fleet. The FAA must be notified immediately upon determination of Level 3 Corrosion.

Level 2 and Level 3 Corrosion finding must be reported to the manufacturer for evaluation and possible Baseline Program adjustment. Corrective fleet actions resulting from Level 3 Corrosion findings must be reported to the FAA.

Although baselines are provided by the manufacturer of an aircraft model it is always the operators responsibility to ensure proper care and treatment of the aircraft. The manufacturer is no longer responsible for the aircraft an any issues resulting from improper care once the operator accepts the aircraft. This is often negated in regards to a new aircraft model that has safety of flight issues that may result in grounding of the entire model and as such the manufacturer may take additional steps in order to ensure customer satisfaction.

Proper Maintenance

In order for an airline to be considered airworthy they have to have a proper maintenance program in place. Many regulatory authorities require to know where the maintenance will be performed and if that maintenance facility has the correct type certificate to perform the work for the commercial aircraft.

To become a certified 14 CFR Part 145 Repair Station there are 5 major phases (Federal Aviation Administration, 2013):

Phase 1 - Preapplication

• Submit a preapplication statement of intent (PASI) to show intent to initiate the certification process.
• Preapplication meeting: held in the district office allowing applicant to become familiar with assigned FAA personnel.
• Application for Repair Certificate and/or Rating: applicant is instructed on how to complete the application
• Formal Application Attachments: Requirements for application attachments are discussed to include the following: Develop and evaluate a repair station manual (RSM) and quality control manual (QCM), Letter of Compliance is completed to ensure compliance with regulations and how the repair station will comply with them
• Letter stating compliance with 14 CFR 145.53(c) or (d)

Phase 2 - Formal Application

• A team of certification team members and all key management personnel will meet with the FAA to ensure all documents are ready for processing and any questions are answered.
• Corporation Papers: If a corporation is making the application the FAA requires a copy of the Certificate of Incorporation by the State.
• Drug and Alcohol Program: A copy of the program must be approved by the FAA.

Phase 3 - Document Compliance

• Application is thoroughly reviewed for approval or disapproval.
• Manual and related attachments are reviewed for acceptance or rejection.

Phase 4 - Demonstration and Inspection

• Certification team ensures the applicants proposed procedures are effective and the facilities and equipment met regulatory requirements.

Phase 5 - Certification

• Once applicant meets regulatory requirements of CFR Part 145 the repair station certificate and operations specifications with the appropriate ratings are issued.

Even with a properly certified repair station performing the work it is ultimately the owner of the aircraft's responsibility to ensure that all maintenance procedures and practices are being followed. Many times maintenance is performed in a different country then where the aircraft is operated and as such may require additional oversight to ensure the airworthiness of the aircraft.

Conclusion:

Although there are ways to prevent an aircraft from rapidly aging it is still recommended to understand what the ultimate life of the aircraft is as recommended by the manufacturer and FAA. Once the aircraft has reached the determined flight hours or flight cycles which deem the aircraft past economic life it is recommended that the aircraft be retired. Just because the airframe reaches its life expiration does not prevent the operator from using parts from the airplane to continue operation of the fleet. There has been little evidence that there is an economic life for engines, landing gear, electronics, or other components that are installed on the aircraft. This may result in many "hanger queens" which tend to be aircraft used for parts only. 

Ultimately the responsibility of the airworthiness and safety of an aircraft lies with the operator of the airplane. Outsourcing maintenance to appropriately certified maintenance facilities is not an excuse for anything that is missed during maintenance. An operator has the right to request additional non-routine work in order to ensure that all maintenance tasks and airworthiness directives are complied with in a timely manner even if the required task or AD is not required for an additional amount of time. It is always better to pull forward maintenance that can assist in preventing added aging then to ignore it.

Aviation Safety Bureau. (2010). How to Prevent Aircraft Corrosion. Retrieved July 2, 2014, from Aviation Safety Bureau website: http://www.aviation-safety-bureau.com/aircraft-corrosion.html

Federal Aviation Administration. (1993, November 29). 8300.12 Corrosion Prevention and Control Programs. Retrieved July 2, 2014, from Regulatory and Guidance Library Web site: http://www.faa.gov/regulations_policies/orders_notices/index.cfm/go/document.information/documentID/11770

Federal Aviation Administration. (2013, March 19). Become a Certificated 14 CFR Part 145 Repair Station. Retrieved July 2, 2014, from Federal Aviation Administration Web site: http://www.faa.gov/aircraft/repair/become/