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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