Understanding MSG
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Understanding MSG-3
By Charlotte Adams, Contributing Editor
Hearing the acronym MSG might make some think of the preservative in some take-out
food. But in the maintenance world, MSG-3 is the root of all inspection schedules in a
process starting before an aircraft enters service. Here is a look at this fascinating process
and how manufacturers and operators work to achieve the end result.
The method that aircraft manufacturers, operators and regulators use to develop the
manufacturers initial maintenance schedule, as part of the work towards aircraft
certification, is beyond the ken of many in the hands-on maintenance world. It is often a
multi-year process, involving the application of rigorous logic, the analysis of reams of
data and the interaction of multiple administrative bodies. Many people, hearing the
acronym MSG, might think its a version of the food additive, monosodium glutamate.
All the more reason to know more about aviations Maintenance Steering Group-3, or
MSG-3, process. It starts before an aircraft enters service, when there is no in-service
operational data, and continues through the life of the type. MSG-3 practitioners are the
Industry Steering Committee (ISC) working groups. Working group members, who are
specialists in the various aircraft systems, interact with members of the manufacturers
design group and receive data from the manufacturer, such as mean time between failure.
But it is the working group members who do the detailed analysis and generate proposed
scheduled maintenance tasks. The working group members representatives of the
manufacturer and operators present their results to the ISC, which approves it.
Representatives of the regulators attend ISC meetings as advisers.
The final output of the ISC for a new aircraft is the Maintenance Review Board Report
(MRBR), which outlines the recommended minimum initial maintenance requirements. This
document is then approved by the FAA, as the MRB chairman (for a U.S. aircraft). The
MSG-3 process provides for tasks, such as lubrication, visual inspections, operational or
functional checks, restoration and discard. (Discard refers to removing life-limited parts
and replacing them with new ones.)
Although there is no actual in-service operational data available when the ISC process
begins for a new aircraft, there is much historical data on the performance of similar
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components and systems used in earlier designs, as well as test data from the
manufacturer and component vendors. "Its the actual in-service reliability data of similar
components and systems that drives the interval," according to Ray Smith, a Boeing
technical principal and the co-chairman of the 787 ISC.
MSG-3 stresses a top-down approach to analysis that starts at the highest manageable
level and looks at the consequences of that failure, explains Dave Nakata, vice president
of EmpowerMX, an MSG-3 consulting service. But safety is key. If MSG-3 analysis shows
that a certain functional failure would jeopardize operational safety, and couldnt be
rectified by any of the hierarchy of standard tasks within the specified logic, then redesign
of the item in question would be mandatory. Application of MSG-3 logic to the emerging
Boeing 787-8 aircraft, for example, has led to mandatory design changes in flight control
and lightning/HIRF (High-Intensity Radiated Field) protection systems, Smith says.
MSG-3 is the only game in town for commercial airplane manufacturers. According to
Advisory Circular AC-121-22A, FAApolicy states that the "latest MSG analysis procedures
must be used for the development of MRBRs for all new or derivative [Part 121] aircraft."
It is the "only methodology accepted by the airworthiness authorities," states Jrg Coelius,
section manager for maintenance programs with Lufthansa Technik. Although MROs are
executors rather than decision makers in the MSG-3 community, LHT is knowledgeable. It
helped develop MSG-3-based maintenance programs for Southwest Airlines, Alaska
Airlines and Lufthansa.
FAA stresses the safety aspects of MSG-3. The methodology "helps improve safety by
addressing hidden functional failures," officials said. "Maintenance-significant items are
addressed at the system level instead of at the parts level." MSG-3 also helps improve
maintenance efficiency, FAA notes, by eliminating redundant and ineffective tasks. There
is usually a substantial cost reduction in hard time component removal and replacement.
The agency also praised MSG-3s thoroughness. The methodology focuses on aircraft
systems and the loss of system function or functions, FAA officials said. It considers
hidden failures, plus one additional failure, in the decision logic, identifies three
consequences of a loss of function (safety, operational, and economic), identifies two
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types of safety tasks, and identifies at least nine types of scheduled maintenance tasks.
MSG-1 and 2, by contrast, focused on parts and part failure rates, considered only one
failure in the decision logic and didnt identify any tasks it was process-oriented rather
than task-oriented.
MSG-3 has also been adopted by most major bizjet manufacturers, with the
encouragement of the National Business Aviation Association (NBAA). Bombardier was the
first proponent, but Gulfstream, Embraer, Cessna and Dassault Falcon Jet, among others,
have embraced the methodology (See sidebar, page 30). One can argue that the bizjet
original equipment manufacturers (OEMs) were better off under the old approach, which
stressed hard time and on-condition maintenance. They had a steady revenue stream
based on predictable parts replacement intervals. But it wasnt cost-effective for the
operators, explains Len Beauchemin, managing director of AeroTechna Solutions, an MSG-
3 consultancy and training company.
B787
The MSG-3 process for the 787-8 started in 2005 and the FAA approved the scheduled
maintenance program in 2008. While 787-8 activities will continue through flight test and
the life of the airplane, ISC work regarding the 787-9 is expected to get under way in
October 2009.
The 787 ISC included seven working groups: systems; electrical and avionics; lightning
and HIRF; powerplant; flight controls and hydraulics; structural; and zonal, says Lynne
Thompson, Boeings director of maintenance engineering.
Its often said that MSG-3 is a task-oriented system, so analysis engineers go through a
prescribed logic sequence, asking questions, depending on the category of the failure
under consideration. A task is then selected to identify or rectify the failure.
A working groups system-level thought process concerning loss of hydraulic pressure, for
example, might go as follows:
How might hydraulic pressure be lost for the right, left or center hydraulic system?
Via an inoperational pump, failed valve, leak in tubing, etc.
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What tasks are required that are applicable and effective to ensure that the hydraulicsystem is maintained to the level of reliability that the manufacturer designed and certified
the system to operate at?
Then those tasks would be added to the scheduled maintenance program if approved bythe ISC.
With MSG-3, "youre looking at the results of the failure instead of worrying about the
failure, itself," Nakata says. System-level analysis of an hydraulic functional failure, for
example, might focus on the failure of the hydraulic distribution system and its
consequences. Even this might not rise to the level of a safety impact if the aircraft, as is
common today, has multiple redundant hydraulic systems. In the context of design
redundancy, MSG-3s top-down approach, which starts at the system level and eventually
works down to the component level, results in fewer maintenance tasks, Coelius points
out.
The MSG-3 document provides logic "trees" for systems and powerplant analysis,
structural analysis, zonal analysis and lightning/HIRF analysis. In the systems/powerplant
diagram, for example, the decision logic divides possible failure effects into five categories,
depending on whether the functional failure is evident to the flight crew. These are:
evident safety, evident operational, evident economic, hidden safety and hidden non-
safety. The tasks resulting from the evident safety and hidden safety categories are the
most critical ones, Coelius says.
Economics
Economics is an important consideration, however. In MSG-3 logic "the sequence of
intervention follows an order of least expensive to most expensive, in order to test the
effectivity of the least expensive task first," explains Kevin Berger of FedEx, the most
recent chairman of a key MSG-3 panel. This progression is true for the MSG-3 logic dealing
with system/powerplants as well as zonal, Berger says. In each case the technical
engineers must answer the question if the task lubrication, inspection, functional check,
restoration, discard is applicable and effective at ensuring operational safety ormitigating the consequences, e.g., operational or economic, to an acceptable level?
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Structural analysis follows a similar path. A visual inspection would be the first choice to
be considered, followed by a detailed inspection and then by special detailed
inspection/NDI, Berger says. "A subtle difference with the structural analysis focuses on
the deductibility of the degradation from accidental damage, environmental damage or
fatigue damage."
MSG-3 logic is much more detailed and "surgical," compared with MSG-2, and continues to
evolve with industry experience and technology, Berger says. This enables the
"manufacturers, operators and regulators to design, operate and insure industry safety
with increasingly safer equipment and more efficient maintenance requirements." Previous
approaches led to unnecessary maintenance tasks, which could "induce potential damage
and cause supplemental failures."
This was like performing surgery on a person just to look at his liver, when the operation
might cause all sorts of other problems.
MSG-3 Changes
The MSG-3 document, "Operator/Manufacturer Scheduled Maintenance Development," is
owned by the Air Transport Association (ATA). But it is constantly evolving, changing
almost every year. Revisions are considered and, if approved, are forwarded by the
Maintenance Program Industry Group (MPIG) to the International MRB Policy Board, which
represents the regulators. The policy board, in its latest meeting of March/April 2009,
approved several notable changes.
One of the accepted proposals concerned structural health monitoring. "This technology is
in the R&D phase, but it was important for industry to provision some policy language to
help promote R&D," explains Berger, the most recent MPIG chairman.
The policy board also decided that manufacturers need to maintain MRBRs for MSG-2 as
well as MSG-3, as long as there are operators relying on MSG-2-derived maintenance
programs. There are still a number of operators using MSG-2.
A third proposal approved by the policy board regarded Issue Paper 44, which prescribes
guidance to evolve existing MRBRs. The new guidelines provide for statistical confidencefactors to be met, based on empirical data collected from the operators. Previous MRBR
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evolutions contained OEM-sponsored analysis, supported by airline in-service data, that
provided sufficient confidence and met the test of ISC approvals, but there hadnt really
been an industry standard for how it was done.
The new guidelines, along with a data format specification known as ATA SPEC2000, will
help manufacturers like Boeing to have statistically significant data for optimizing and
developing maintenance programs, Thompson says. "We have to have enough data to be
95 percent confident in suggesting an optimization of a maintenance task."
As a result, Boeing is working with operators to gather more comprehensive, SPEC2000-
formatted data in its In Service Data Program (ISDP), which currently involves just over 50
percent of the companys airline customers. ISDP is used to understand the safety of the
fleet, decide whether a service bulletin or design change may be required and optimize
maintenance programs, Thompson said. The impact would be significant. "Instead of
having a conversation about what the intervals should be, well be able to use improved
statistical methods to determine what the intervals should be." The guidelines, however,
are discretionary for air carriers that have approved regulatory processes for maintenance
program adjustments.
Boeings most active ISCs meet about every year to analyze in-service data from both
scheduled and unscheduled maintenance and make recommendations to optimize (add
or delete) tasks, Thompson says. "We may lower or raise the intervals based on service
information." Boeing maintains MSG-2 and MSG-3 programs for all the airplane models
except the 707 and the BBJ.
An airline can transition to the updated OEM program or deviate from it, based on its own
substantiated in-service experience. Based on their own data, airlines may choose to
increase or decrease the intervals, with local FAA approval. "Most of them add many
additional tasks, based on their operational requirements, airline policies and customer
goals," Smith says.
MSG-3 and STCs
When there are major changes to an aircraft type, such as a passenger-to-freighterconversion, the STC applicant or holder must address required Instructions for Continued
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Airworthiness (ICA). The STC applicant must show the certification office what existing
requirements for the type (contained in the MRBR) are affected by the modification and
what new ICA are required to maintain the scope of the STC. How to accomplish this is up
to the STC holder, but regulators expect full knowledge of MSG-3.
Some STC holders convene "mini ISCs" if the scope of the STC is very large. More
frequently, however, the work is handled through less formal coordination between the
regulator, the design engineers and the operators. ST Aerospace took the less formal
approach with its STC for the B757 freighter conversion. The company has subsequently
submitted an "appendix proposal" to Boeing to supplement the current MRBR.
Operator review in this case was performed exclusively by FedEx, since the cargo carrier
was the only user of the ST Aero P-F derivative B757 freighter at the time, according to
Berger. The STC resulted in changes to B757 systems such as hydraulics, pneumatics,
cabin, oxygen and structure, although the airplanes basic operating characteristics
remained the same.
ST Aero had to address ICA associated with the B757 conversion. The company had to
reevaluate the MSG-3 MRBR and "discount those things that werent applicable to the
freighter version and supplement that with things that now are applicable because of the
things they changed," Berger explains. The STC applicants design office then had to
produce analyses in order to get their STC approved by the regulator in this case the
FAA.
Business Aviation
Led by Bombardier, most major business aviation manufacturers use the Maintenance
Steering Group-3 (MSG-3) methodology in developing their recommended maintenance
plans for recent-model aircraft. Like commercial aircraft makers, bizjet manufacturers
convene Industry Steering Committees (ISCs) which produce Maintenance Review Board
Reports (MRBRs), and these MRBRs are then approved by FAA or appropriate national
aviation authorities. If a manufacturer later makes changes to the approved program,
these have to be reviewed and okayed by the regulator as well.
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Part 91 (Title 14 CFR 91.409) requires a business aircraft operator to select an inspection
program, and, because of the limited analytic resources of individual companies, operators
select the current inspection program recommended by the manufacturer, whether the
program was MSG-3-derived or not. Len Beauchemin, managing director of AeroTechna
Solutions, an MSG-3 consultancy and training company, toldAviation Maintenancehe
recommends the use of MSG-3-derived inspection/maintenance programs because the
rigorous process, involving manufacturers, operators and regulators, produces safe,
efficient and cost-effective maintenance programs. Otherwise youre relying on the
analysis of original equipment manufacturer (OEM) engineers who may "never have
operated an airplane and may never have seen the part theyre putting a task on."
Once a manufacturer commits itself to following MSG-3, the process leads to an MRBR,
which means heavy regulator involvement. Although this is more time-consuming and
expensive for the airframer than the previous method of developing the maintenance plan
internally, there are benefits. OEMs are able to gather valuable reliability data from the
operators about how products are performing in the field. The MSG-3 route is attractive to
operators because they have more input into the aircraft development process and enjoy
greater efficiencies and cost savings.
"I havent seen an [MSG-3-derived] program that hasnt produced savings," particularly in
engine maintenance costs, Beauchemin adds. Cost reductions in scheduled maintenance
programs range up to 30 percent.
The MSG-3 process influences design in business aviation, as well as commercial aviation.
While Beauchemin was working for Eastman Kodak as director of maintenance and
aviation department co-manager, he served as chairman of the ISC for Bombardiers
Global business jets. ISC input resulted in design changes for inspectability, he says. The
committee would look at proposed tasks and then go to the airplane and try to perform
them, he explains. This interaction with design engineers resulted in changes such as the
addition of access panels and doors.
In business as well as commercial aviation, MRBRs evolve, as more operational data is
collected and analyzed. The incentive in business aviation to keep ones corporate
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maintenance program updated to the latest changes put forth by the manufacturer is
perhaps greater than in the commercial world, Beauchemin says.
Its a question of asset value management, he explains. Although a corporate operator is
not required to continuously update its maintenance program to match the latest changes
to the MRBR, the aircraft would decrease in resale value if this was not done because the
buyer is required to begin his maintenance program with the manufacturers latest
offering. The buyer would have to spend money performing all the tasks required to bring
the airplanes maintenance program up to date. Charlotte Adams