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Down on downtime: airframers under pressure to develop predictive maintenance systems

Since their introduction roughly a decade ago aircraft health monitoring systems have enabled airlines to make significant strides in reducing flight delays and cancellations due to maintenance problems.

But as those systems are evolving, airframers are under increasing pressure to develop systems enabling carriers to develop predictive maintenance capabilities to sharply cut aircraft downtime and simplify maintenance planning.

All four major airframers are heeding those calls and aggressively working to improve their health monitoring products to ensure technicians receive relevant information from the aircraft to ensure they operate at their full revenue potential.

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Brazilian airframer Embraer estimates that since introducing its aircraft health analysis and diagnosis (AHEAD) tool for its 70-to-122 seat E-Jet family in 2006, the possibility to cut flight interruptions - delays or cancellations - has risen up to 30% due to AHEAD's advanced notification, diagnostics and trouble-shooting capabilities.


Nine carriers use AHEAD, which receives fault messages from the aircraft's central maintenance computer whose monitoring capabilities include flight controls, avionics, hydraulics and landing gear and all other major aircraft systems.

 © Boeing
Boeing is using the aircraft monitoring system developed for its 777 as a baseline for the 787

Embraer's CMC can generate 4,000 fault messages through the monitoring of roughly 15,000 data parameters on the aircraft.

Company head of market intelligence Luiz Chiessi says that in its next phase AHEAD will begin monitoring parameters to supply operators prognostic information.

But the ultimate goal is moving to predictive maintenance based on the condition of the aircraft, says Chiessi.

He envisions a time when operators can use information collected from health monitoring systems to tailor maintenance to a specific aircraft serial number.

Currently, maintenance steering groups typically use analysis and testing of components to work from a base of the worst average statistics of component reliability and repair to create maintenance planning documents.

Through the evolution of health monitoring Chiessi believes operators will be empowered to precisely monitor the behaviour of a given component or structure, resulting in an extension of their time on the aircraft.

 © Embraer
Embraer's AHEAD monitors 15,000 data parameters on an aircraft's flight controls, avionics, hydraulics and landing gear and other major systems

The shift to a philosophy of aircraft-specific maintenance also allows operators to determine if the degradation rate of a specific component is greater than normal, says Chiessi, further improving dispatch reliability and cutting downtime due to maintenance.

Embraer's Canadian rival Bombardier envisions a similar shift to monitoring the degradation of a given aircraft component.

Although the company is roughly a year away from having its specific health monitoring architecture defined for the CSeries Bombardier CSeries programme, director Benjamin Boehm agrees the trend in maintenance, repair and overhaul is progressing toward a more predictive nature rather than carriers operating in a reactive mode.

To illustrate that point, Boehm explains the shift to LED lighting in the CSeries means the airframer and operators will be able to monitor the luminosity of the lights, and when they reach a certain level the airline can plan accordingly rather than receiving a frantic message that a light bulb has blown.

Predictive modelling is also incorporated into the CSeries' electronic braking system. Boehm says Bombardier opted for electronic brakes after conducting a trade study analysis on the new family.

The electronic actuator gauges the pressure being applied to the brake pad, and allows the operator to monitor the wear. For example, says Boehm, a carrier determining the pads are at a notional 60% wear can decide "okay, during the next overnight I'm going to replace the brake pads rather than wait until they hit the limit".

Human factors are also important as Bombardier develops health monitoring capabilities for the CSeries. The company envisions that carriers ultimately choosing the aircraft will have business models of varying complexity.

To support airlines with more remote outstations in their network, Bombardier is developing a series of plug-ins on the CSeries landing gear bay, avionics bay and auxiliary power unit area for technicians to use their laptops at the aircraft instead of walking back and forth from the station. "

It is all about time and data," says Boehm, who notes that even when developing tools for predictive maintenance capabilities on aircraft, the human dimension still needs consideration.


Boeing is also incorporating the practical needs of technicians in 787 maintenance monitoring. The company's 787 chief mechanic Justin Hale says Boeing is developing a wireless system unique to the aircraft allowing mechanics to access fault and support data, run tests in real time and "go wherever they need to," in order to perform the required task.

Evolution of health monitoring is also creating opportunities for airframers to offer monitoring and data collection for non-essential systems, such as galley cooling. Boeing's Hale says galley chillers are a notoriously unreliable part of the aircraft that frequently cause schedule disruptions. Boeing will therefore introduce fully integrated health monitoring for galleys on the 787.

Using the aircraft monitoring system for its 777 as a baseline on the 787, Boeing expects to expand the number of reportable maintenance messages from 13,000-14,000 on the 777 to roughly 20,000 on the 787. Monitoring on the 787 is broadening to cover elements currently not available on the 777, such as payload systems, including cargo handling, passenger service units and water and waste systems.

From a broader perspective the goal on 787 health monitoring is to improve fault isolation. Rick Reuter, Integrated Health Management Leader on the central maintenance computing function, says that on the 787 Boeing is targeting areas it identified for improvement on the 777 to supply more accurate information to a mechanic to improve his or her ability to focus on a specific problem.

On the 787 Boeing is improving the algorithms to both enable more accurate correlation between maintenance and pilot indications produced by the aircraft and a clearer consolidation of fault conditions reported by aircraft systems.

A failure in one place within highly integrated aircraft systems tends to have a ripple effect, says Hale, making it difficult to trouble- shoot maintenance problems. He says Boeing is creating more robust algorithms and computer processing abilities to isolate fault indications that "point to one problem".

Boeing is also striving on the 787 to reduce inspections that require a large amount of time, but rarely result in any meaningful fault discovery. One example is hard landings where the 787 chief mechanic says most inspections produce no findings.


Specifically, the structural monitoring system related to those hard and heavy landings combines inertial data and aircraft attitude relative to the landing surface. The system on the 787 summarizes the data onboard and presents it to maintenance laptop displays.

Technicians then reference the collected data against tables in maintenance instructions, "which results in inspections targeted only for those areas of structure which have truly seen excessive loading during the landing event", says Hale. Without that system, inspections would be based on a pilot's sense of a hard landing, and further quantified by retrieving sink rate data from the flight recorder.

"If the sink rate data recorded exceeded a given threshold, a full inspection of the aircraft would be initiated, without any understanding of which areas of the aircraft had actually been overstressed," says Hale.

Boeing is also studying other types of structural monitoring, including metallic structure for crack initiation, composite structures for impacts and internal delaminations. Also under consideration is the monitoring of high-lift components for air loads in an overspeed event. Those features are not pegged for the 787 in the near-term, but could be incorporated into future Boeing aircraft models.

Airbus meanwhile is also evolving its Airman health monitoring system through the debut of Rep@ir Manager on its A380 to give technicians "fast assessment and decision for repair", says Airbus maintenance & engineering marketing manager Vanessa Gerencseri.

Built on 2D and 3D graphical interfaces, the goal to make it easier for technicians to locate damage, access records and use Airman's direct link to the structural repair manual to make decisions regarding repairs.

Airbus is working on a new generation of Airman to develop smarter algorithms, and make the tool easier to deploy through a modular framework. The airframer "will integrate the technology evolutions brought by the newest aircraft into the tool and ensure that the existing aircraft families will benefit as much as possible from all the new functions and improvements", Gerencseri says.

Through Airman, Airbus is also improving the management of fault alerts. With the capability to acquire entries from the airframer's eLogbook, Airman combines those entries with flight deck and cockpit effects to build complete fault cases, says Gerencseri, who notes the combining of the two functions supplies technicians with all the necessary information to shorten the process of determining and troubleshooting problems.

Airbus has also broadened the number of reports captured by the aircraft condition monitoring system, putting the information into a central tool for analysis by an operator's engineering teams. Carriers can now also "enrich Airman with their operational experience", says Gerencseri.

Work orders are generated from warning and fault messages with pre-filled information and then sent to an operator's maintenance information system. At the time a maintenance action is performed, results are sent back to Airman, which remembers that particular experience and supplies the effectiveness of the fix to an operator.


As airframers improve the ability of their aircraft to produce reams of data to help operators maximize maintenance planning and trouble shooting, new challenges are created for operators as they attempt to harness the data produced by the aircraft.

Bombardier's Boehm says the airframer has heard several complaints from carriers that each manufacturer has different software for analysing the data on the ground. He points to one carrier that was considering the introduction of another fleet type, but ultimately decided against the purchase after it determined it would cost many millions to develop changes to its ground data management infrastructure to incorporate the new aircraft into its fleet. Boehm says Bombardier is trying to avoid that level of introductory cost with the CSeries.

Bombardier sees a trend of carriers preferring raw data since it can allow airlines to customize the data for their specific operations.

The increasing volume of data generated by an aircraft also has other practical implications as Bombardier's Boehm points out that larger antennas might be required to transmit it. Carriers also have to distinguish between the critical data necessary for transmittal while in flight and the non-critical information that can be downloaded on the ground through less expensive methods.

Ultimately, however, as data collection generates its own challenges all airframers have the overarching goal of increasing reliability and reducing costs, says Chiessi of Embraer.

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