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Wednesday, July 1, 2009

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 manufacturer’s 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 it’s a version of the food additive, monosodium glutamate.

All the more reason to know more about aviation’s 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 manufacturer’s 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 components and systems used in earlier designs, as well as test data from the manufacturer and component vendors. "It’s 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 couldn’t 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, FAA policy 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 Jörg 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-3’s 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 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 didn’t 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 wasn’t cost-effective for the operators, explains Len Beauchemin, managing director of AeroTechna Solutions, an MSG-3 consultancy and training company.


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, Boeing’s director of maintenance engineering.

It’s 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 group’s 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.

  • What tasks are required that are applicable and effective to ensure that the hydraulic system 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 by the ISC.

With MSG-3, "you’re 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-3’s 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 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 or mitigating the consequences, e.g., operational or economic, to an acceptable level?

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 confidence factors to be met, based on empirical data collected from the operators. Previous MRBR evolutions contained OEM-sponsored analysis, supported by airline in-service data, that provided sufficient confidence and met the test of ISC approvals, but there hadn’t 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 company’s 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, we’ll 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.

Boeing’s 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-freighter conversion, the STC applicant or holder must address required Instructions for Continued 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 airplane’s 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 weren’t applicable to the freighter version and supplement that with things that now are applicable because of the things they changed," Berger explains. The STC applicant’s 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.

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, told Aviation Maintenance he 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 you’re relying on the analysis of original equipment manufacturer (OEM) engineers who may "never have operated an airplane and may never have seen the part they’re 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 haven’t seen an [MSG-3-derived] program that hasn’t 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 Bombardier’s 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 one’s corporate maintenance program updated to the latest changes put forth by the manufacturer is perhaps greater than in the commercial world, Beauchemin says.

It’s 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 manufacturer’s latest offering. The buyer would have to spend money performing all the tasks required to bring the airplane’s maintenance program up to date. — Charlotte Adams

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