the average age of commercial airplanes currently in service increases,
concerns continue to be raised about existing maintenance programs
and how effectively they can help ensure the continued airworthiness
of older airplanes. Although no specific deficiencies have been identified,
the U.S. Federal Aviation Administration (FAA) and industry representatives
are working together on a program to address these concerns. The purpose
of the program is to determine what action must be taken to mitigate
the effects of age on systems in older airplanes.
63 percent of the 10,500 Boeing commercial airplanes in service
were built according to type designs that are more than 20 years
old. These airplanes may not be more than 20 years old, but all
Boeing DC-8, DC-9, DC-10, 707, 727, 737-100/-200, and 747-100/-200/-300
airplanes were designed before 1979 and have accumulated 67 percent
of the 403 million total hours flown. A plan that responds to concerns
about the condition of aging nonstructural systems on these airplanes
was recently released. The plan resulted from a program similar
to one established in 1988 to evaluate aging airplane structures.
The U.S. White
House Commission on Aviation Safety and Security recommended that
the FAA work with operators and original equipment manufacturers
(OEM) to expand the aging aircraft program to include nonstructural
components. The plan released by the FAA last year outlines seven
initiatives to address aging airplane systems:
an aging transport systems oversight committee to coordinate the
various aging systems initiatives within the FAA.
- Conduct an
in-depth review of the aging transport fleet and make model-specific
safety recommendations related to airplane systems.
- Enhance airplane
maintenance to better address aging airplane systems.
- Add aging
systems tasks to the aging airplane research program.
- Improve reporting
of accident, incident, and maintenance actions involving wiring
- Evaluate the
need for additional maintenance of transport airplane fuel system
wiring and address any potentially unsafe conditions.
- Improve wiring
installation drawings and instructions for continuing airworthiness.
year, the FAA formed a committee to propose revisions to applicable
Federal Aviation Regulations and associated guidance material. The
goal of the committee is to revise the materials as necessary to
ensure the continued airworthiness of nonstructural systems on aging
Known as the
Aging Transport Systems Rulemaking Advisory Committee (RAC), the
group includes representatives of the Aerospace Industries Association
of America, Air Transport Association, Air Line Pilots Association,
Airbus Industrie, America West Airlines, Boeing Commercial Airplanes
Group, European Association of Aerospace Industries, FAA, General
Aviation Manufacturers Association, Joint Aviation Authorities,
National Electrical Manufacturers Association, Transport Canada,
U.S. Department of Defense, and U.S. National Aeronautics and Space
The RAC has developed
five specific tasks to address one or more elements of the FAA plan:
fleet service history.
and update standard practices for wiring.
inspection and repair training programs.
House Commission recommendations, such as evaluating the need for
additional maintenance of commercial airplane fuel-system wiring,
are being addressed in separate industry programs.
EVALUATE FLEET CONDITION
The first task will be to conduct a sampling inspection of the fleet,
to include establishing the airplane models to be evaluated, determining
the evaluation criteria, developing a plan, and evaluating the fleet.
Airplanes to be surveyed include those undergoing heavy maintenance,
those sitting out of service, and those representing newer airplanes
of each affected model.
undergoing heavy maintenance.
The applicable OEM and airline representatives for each airplane
model have identified significant electrical systems that are susceptible
to the effects of aging. They plan to survey those systems on older
airplanes for which previous inspection data does not exist or is
incomplete. Surveys of wiring and related electrical systems on
DC-8, DC-9, DC-10, 727, 737, 747, and L-1011 airplanes were scheduled
to be completed in May 1999, when the RAC was slated to review the
results. Surveys of the Airbus A300, which was recently added to
the roster of aging airplanes, are expected to be complete in December
sitting out of service.
The condition of systems on recently retired airplanes that are
no longer economically feasible for commercial service operation
will also be evaluated. Intrusive, detailed examination of these
airplanes should identify conditions that could potentially affect
the proper operation of similar systems on airplanes still in service.
Newer airplanes representing
Information from surveys of both in-service airplanes and recently
retired airplanes will be used to survey newer airplanes that represent
the affected models. This aspect determines at which point general
conditions related to aging begin to appear. The results will be
reflected in recommendations for proper maintenance intervals.
Because of the complexity
and difficulty of reporting incidents on electrical systems and
because of the difficulty in obtaining historical data specific
to airplane wiring, the short-term focus will be on electrical systems.
A decision whether surveys of other airplane systems are required
will be made at the end of 1999.
REVIEW FLEET SERVICE HISTORY
As airplanes age, changes in operational, maintenance, and design
practices prompt production changes to the airplane that cause the
design to continuously evolve. Many changes benefit operators and
are offered for retrofit on earlier airplanes. Operator and regulatory
consideration of these postdelivery changes for airplane fleet installation
is based on economic and safety factors. If a change is not immediately
mandated by regulatory agencies, economic factors determine whether
any postdelivery changes are installed on commercial airplanes.
The service history of
each airplane model will also be evaluated to determine whether
to recommend that the FAA mandate certain production modifications
on in-service airplanes. Depending on the outcome of this evaluation,
a similar program may be instituted on airplanes with type designs
less than 20 years old.
IMPROVE MAINTENANCE CRITERIA
recommends a general plan for maintenance of each airplane model,
but many operators customize these plans based on their unique requirements
and experiences. These maintenance plans are reviewed and approved
by the applicable regulatory agencies but may not completely address
the effects of aging. The FAA has recommended that general maintenance
procedures be evaluated and that a model-specific maintenance program
Specific areas under
review are developing an improved electrical system inspection criteria;
defining practices to eliminate wire bundle contamination or damage;
determining an acceptable criteria for corrosion of components;
establishing a process to link line, base, and shop maintenance
actions; and reviewing the maintenance steering group-3 (MSG-3)
process. The effects of aging noted during the surveys of both in-service
and out-of-service airplanes will be considered when updating the
criteria. The MSG-3 process establishes the initial minimum maintenance
and inspection requirements for operators to use when developing
an approved continuous airworthiness maintenance program for airframe,
engines, systems, and components.
REVIEW AND UPDATE STANDARD PRACTICES FOR WIRING
The FAA has recommended that operators and the OEM develop a customized
standard wiring practices manual to clarify and simplify electrical
system installation and repair practices. This manual provides procedures
for all types of electrical parts, some of which may not be used
by a particular maintenance or repair facility. Removing unnecessary
information and tailoring the procedures to specific repair facilities
are expected to streamline the repair of electrical components.
In addition, the FAA
recommended that a process that trains maintenance personnel to
recognize aging effects on electrical
systems and alerts them to proper repair procedures be defined.
REVIEW INSPECTION AND REPAIR TRAINING PROGRAMS
As with maintenance programs, operators also customize their inspection
and repair training programs based on their own requirements. The
FAA has recommended collecting the best practices from each training
program and establishing a model inspection and repair training
program that reflects industry best practices.
The Air Transport Association
has already compiled some best practices from its member airlines,
including operator-amended recommendations from Boeing on proven
maintenance, training, and procedural practices. This information
will serve as the basis for a maintenance best-practices videotape
and any future inspection and repair training programs.
monitoring its in-service airplanes and conducting an historical
analysis of airplane accidents, Boeing has not identified
aging aircraft systems as a major problem. These results are
based on data from thousands of airplanes that have accumulated
millions of flight hours over the last 25 years. As the result
of scheduled and unscheduled line and base maintenance, many
nonstructural system components and the wires, tubes, and
hoses that link these components are inspected, repaired,
or replaced. However, Boeing is working with the aviation
industry on a program established by the FAA to assess the
effects of age on systems in older airplanes. When completed,
the program will provide all members of the industry with
the necessary information to ensure the continued safety of
nonstructural systems on these airplanes.
BOEING COMMERCIAL AIRPLANES GROUP