Fault-Free Flying

As anyone in the airline industry will tell you, maintenance and repair represents a big slice of an aircraft’s total operating costs. Although estimates vary, and simple figures are misleading, industry surveys put the cost of running repairs at anything between 10% and 45% of annual expenses, depending on the class, type and age of the aircraft.

These are not just the costs of parts and labour, but also of mechanical delays, so there’s clear value in systems that transmit fault data to airline operation centres and allow maintenance crews to be ready with the right LRU or rotable when the plane lands.

The onboard technology is nothing new – for example Boeing first incorporated it into the 747-400 in the late 1980s, in the form of a central maintenance computer (CMC) that collects fault data from various system components – but it’s the real-time datalink with the ground that’s getting aerospace manufacturers and airline operators interested.

Honeywell Aerospace’s latest CIS / MS (crew information system / maintenance system) is a case in point. One of a growing number of AHM (aircraft health monitoring) systems, it’s being fitted to Boeing’s 787, within the CMC.

AHM is the overarching technology of managing all the ‘member’ systems onboard an aircraft, from flight control systems to in-flight entertainment; on the 787 more than 150 key systems are monitored.

The technology underlying the CIS / MS is a model-based fault propagation model and suite of knowledge management tools to define the relationships between member systems and LRUs, and the defined behaviours of these systems.

Honeywell’s vice-president of aerospace services, marketing and product management Michael Edmonds says, “With this detailed understanding of the relationships between the member systems the CIS / MS is able to interpret over 100,000 parameters and 30,000 fault conditions in order to provide specific maintenance actions and concise crew alerts.

“Additionally, the system provides an aircraft condition monitoring function to provide standard and customised aircraft reports to the operator. It also includes a secure wireless connection to provide the aircraft health information to the ground and the line maintenance staff.”

Onboard technologies

From Boeing’s perspective, onboard technologies focus on data collection and storage at the component level, as well as the ability to transmit the data offboard. “For example,” explains Dave Kinney, Boeing’s airplane health management product manager, “what used to be a simple electromechanical valve with a power supply is now a more complex component that might record and transmit valve state (% open) and cycles (how many times it’s transitioned). This data can support diagnosis of how the overall system is behaving or how close the valve might be to failure or overhaul.”

The other primary component is of course offboard – the data warehousing and further data analysis function – which also handles the interfacing to the maintenance teams, engineers and managers who use the data to support their day-to-day operational decision-making. An obvious key application area here is high-cost components, says Kinney.

“Better information on failure conditions and related data of these parts speeds up the troubleshooting and repair process,” he explains.

“A key metric to any component is the no fault found (NFF) rate. If a component is removed during troubleshooting and tests OK in the shop – that is, NFF – then the operator has just spent a bunch of time / effort / money removing a good component. A successful AHM system will reduce the cases of NFF, especially on high-value assets.

“A clear benefit of keeping NFF low is that it reduces the number of parts in circulation and spares stores, thus reducing airline and manufacturer operating costs.”

Airbus has a similar AHM system in place but the company had not responded to requests for information about it by the time of writing. All that can be said here is the onboard application is called AIRMAN (aircraft maintenance analysis) while the ground-based support facility, in Toulouse, is called AIRTAC (airbus technical aircraft-on-ground centre). And all Bombardier is able to say at this stage is that its own system is under development.

Embraer by contrast has been offering its AHEAD (Aircraft Health Analysis and Diagnosis) system since 2006 to all operators of its E-Jets. Like the Honeywell system, it automatically generates and transmits real-time warning messages to a ground base.

The technology will not be available to every operator though. While Boeing considers the onboard component essential for any new aircraft type, retrofits (at least of a CMC) will not be feasible owing to the extensive integration and databus architecture needed to enable it to work. However, says Kinney, “To mitigate this on aircraft that do not have a CMC, such as the 737NG, Boeing is looking to other onboard data collection and analysis methods, specifically working with the digital flight data acquisition unit and airplane condition monitoring system, which have been installed on airplanes in one form or another since the 1950s.”

The offboard side

Meanwhile the offboard component, he says, is typically part of aftermarket services, and therefore requires an airline to pass a business case analysis justifying the purchase. “However, airlines are increasingly considering a highly functioning offboard HM component a must-have,” he says.

One such airline that has taken this step is British Airways, which in March 2010 signed a five-year deal with Boeing to use its offboard AHM service across the airline’s 747s, 777s and, from 2012, its new fleet of 787s.

Manufacturers are stepping up to the plate as well. For example, in June 2011, Rolls-Royce announced an integrated data service with Boeing that will allow health data from Rolls-Royce engines on Boeing aircraft to be combined on a single system and sent to the aircraft’s operator.

The service is available to airlines with both Rolls-Royce engine health monitoring (EHM) and Boeing AHM data, and will initially be available for the Trent 1000/Boeing 787 and the Trent 800/777 combinations.

By the end of 2011 it will also cover RB211-524/Boeing 747 and RB211-535/757 combinations.

And there’s more to come in the future, such as autonomous collection, storage and reporting of data on the condition of an aircraft’s structure. Boeing for one is investing in this technology, with, says Kinney, “the expectation that it will one day be a fully participating member system.” That of course will be another story.