Condition Based Maintenance
Written by Peter Buxbaum
MLF 2010 Volume: 4 Issue: 7 (August)
Is Performing Maintenance Based On A Number Of
Hours Or Cycles The Most Efficient Way To Sustain
Large Fleets? Some Think There Is A Better Way.
Drivers who take good care of their automobiles usually change the oil and perform other maintenance at scheduled intervals, based upon the car manufacturer’s recommendations. That’s also the way the United States military traditionally performed maintenance on its vehicles, weapons systems, and other platforms. If a manufacturer recommended, for example, that an aircraft be brought in for maintenance after 300 hours of flight, the armed services would figure in a safety factor and maintain the platform a little bit sooner than that.
But there is a transition taking place in military maintenance strategy. Instead of performing maintenance at scheduled intervals, there is now greater emphasis on monitoring components and subsystems so that they can be maintained when they need maintenance, and not before.
A series of practices, procedures and technologies called condition based maintenance (CBM) attempt to optimize maintenance tasks, save money and improve machine operational performance. Implementation of CBM requires first of all an analysis of maintenance requirements and priorities. It also involves, especially in the iteration the Department of Defense calls CBM+, the electronic, online monitoring of key subsystems and components for signal processing, detection of incipient failures, and prediction of their remaining useful life.
There is evidence that suggests that platforms monitored through CBM+ exhibit greater reliability and readiness, which saves the armed services money. Some newer platforms have the sensors designed in from the beginning; others must be retrofitted with the technology. Budgetary considerations play a large role in determining whether platforms will be retrofitted with CBM+ technologies.
“CBM attempts to tell you when something needs to be maintained based on its condition rather than just a timetable,” said Chris Amos, senior vice president at the technology solutions group at Aloin Corp. “Timetables are really just a guess based on what is typically needed” to maintain a given platform.
Electronic monitoring of components is designed to detect changes which can predict if a subsystem is in danger of failing. “CBM+ is a DoD proactive equipment maintenance capability that uses system sensor-based health indications to identify and predict functional failure in advance of the event and provides the ability to take appropriate action,” said an Army posture statement on the subject.
"If you are measuring vibrations you would put in an accelerometer,” explained Michael O’Reilly of QinetiQ. “When the signal starts increasing, then from an engineering standpoint something is not right with that component.”
CBM promises a number of benefits to its practitioners. “Operationally it makes platforms like aircraft safer,” said O’Reilly. “There is less risk of a fatal accident as a result of a failed part.”
CBM can also help tighten maintenance budgets by making the parts supply chain more efficient. “They are not changing out parts that still have life to them,” said O’Reilly. “They also are able to order parts when they know they will be needed.”
CBM can also help reduce the total cost of ownership of weapons systems and other platforms. “Studies have shown that 70 percent to 80 percent of the costs of a weapons system are involved in operations and sustainment,” said Bill Berneski, program manager for maintenance and logistics solutions at CACI International. “Only 20 to 30 percent of costs are incurred in the initial design and acquisition. CBM optimizes costs by attacking the highest cost driver. The goal of CBM is to get out in front in thinking about maintenance in the design phase so that you don’t find out only later that the platform is too expensive to maintain.”
The precursor to CBM is an analysis performed under a methodology called reliability centered maintenance, or RCM. “RCM determines what the maintenance requirements are,” explained Berneski, “and what you need to do to prevent a system from failing. RCM tells you what to do; CBM determines how to do it and how often.”
That means that an RCM analysis would not necessarily yield a conclusion that a component be monitored electronically. In the case of inexpensive and non-critical components, the answer might actually be to let the part fail before replacing it.
RCM is a four-step process which analyzes systems, defines essential functions and subsystems, predicts possible failure modes and develops procedures to prevent failure.
“Once you’ve completed RCM, you end up with a list of maintenance requirements to keep a system operating,” said Berneski. “Then you figure out how you will go about doing this. Sometimes the answer is going to be scheduled maintenance, sometimes it is going to be periodic inspections, and sometimes you will want to rely on data gathered electronically. All of this holistically becomes CBM.”
“What is in vogue today,” Berneski added, “is the application of technology to have the equipment tell you when you need to do maintenance. Embedded sensors alert operators to schedule maintenance.”
This electronic monitoring, or CBM+, involves the collection of data on the platform, moving the data off the platform to a data warehouse, analyzing the data and acting on the data. “CBM+ has the potential to provide the Army unprecedented visibility of its systems,” said the Army posture statement. “Program managers are incrementally applying CBM+ technologies to existing platforms where feasible.”
At this point, around 30 percent of the Army’s aircraft have been equipped with digital source collectors. Army aircraft deployed to Afghanistan and Iraq wirelessly transmit data on a basis daily from the aircraft logbook to a home base. “These technologies have been credited with averting Apaches and Blackhawks from critical failures,” said the Army Posture Statement. “Soldiers in the field are using CBM+ technologies to save lives and equipment.”
Most Army platforms using CBM+ are being retrofitted with the requisite sensors. New Apaches coming of the assembly line have the sensor technology built in, as will the F-35 Joint Strike Fighter once it goes into production. Army Stryker vehicles have a fair amount of electronic instrumentation built in, according to Amos, while some of the vehicles are being retrofitted with still more sensors.
The Apaches, because they are newer than some other Army aircraft, are easier to retrofit with maintenance monitoring sensors than their older Black Hawk counterparts. “The Apache has a data bus designed with an open architecture, making it easy to add sensors,” explained Amos. “The Black Hawk does not have an open architecture data bus and it is much more difficult to add sensors.”
This explains why 70 percent of the Apache fleet is equipped with sensors, as compared to less than 15 percent of Black Hawks. The Chinooks are even less further along.
The Apache is equipped with multiple engine sensors and several vibration sensors positioned at various parts of the air frame. The engine sensors provide clues to the overall health of the system while vibration sensors provide analysts with a range of information, including how well the platform can aim its weapons systems.
Alion Corp. has been advising the Marine Corps on the effectiveness of its CBM programs. “We started off with one vehicle,” said Amos. “We have been subsequently asked to expand that and now have programs covering over 400 systems, the majority of them fielded. We assess for the Marine Corps how CBM is influencing the operational capabilities of their systems, how much it costs the Marine Corps to achieve that level and how they can improve their CBM practices.”
QinetiQ has built the data warehouse that the Army uses to capture data being transmitted from several of its aircraft. The company has also started to work with Navy aircraft through its Army contract.
“This includes data coming off the aircraft log book on flight times and how and where the aircraft is being flown, along with sensor data on acceleration and vibration,” said O’Reilly. “We pull all that data together and by applying software tools that correlate the data and search for anomalies, provide a picture of the effective life of the components being monitored.”
The system generates a report on data anomalies that scores the platform at one of three levels: green, yellow and red. Red-scored platforms must be maintained immediately while yellow ones must be monitored closely.
The QinetiQ software, having examined data from hundreds of Apache helicopters, is able to predict whether and when other helicopters will have problems similar to the ones detected. It is also able to diagnose problems with aircraft showing the same symptoms as those it is familiar with.
The United States Coast Guard is considering applying sensor technology to some of its legacy cutters, according to Berneski. “They are looking to apply the technology in a smart way, not just because it is available,” he said. “They are examining how the technology can accomplish their maintenance requirements.”
There are a number of challenges associated with implementing CBM+. “It is expensive,” said Amos, especially in the case of the Blackhawk and Chinook helicopters that are difficult to retrofit. “It costs over one million dollars to retrofit each Black Hawk. You have to be reasonably sure you’re going to save considerably more than that over the life of the platform.”
“The trick is not to overdo sensors,” said Berneski. “It doesn’t pay to do much until you have determined what the requirements are through RCM. Otherwise, you can collect terabytes of data, but unless you know your maintenance requirements you are just wasting resources. The costs of technology have come down in recent years, but it is still possible to spend too much money on data collection devices that you don’t need.”
Another problem involves how the military budget game is played in Washington. “CBM typically doesn’t save money until later in a platform/s life cycle,” said Berneski. Maintenance is often not reflected in acquisition costs when the Pentagon is trying to get Congress to fund a program. This makes it more difficult when the Pentagon asks for CBM funding further down the road.
CBM has been documented to provide benefits to its practitioners. An April 2007 Apache helicopter crash provided the Army with data from the vibration sensor on the tail rotor, which provided a clue to the cause of the crash. Armed with that knowledge, the Army was able to identify symptoms of incipient failure on other platforms and bring them in for immediate maintenance to save lives.
According to Amos, the Apache fleet has experienced a 5 percent increase in readiness through CBM while the Black Hawk fleet, which has fewer aircraft electronically monitored, has experienced a 1 percent increase. The difference is explained, he said, by the relative differences in experience between maintenance personnel of the two fleets in reading instrument data.
The Apache results mean, Amos explained, that if “you’ve got a fleet of roughly 300 Apaches, if you have 5 percent higher availability, that’s 15 Apaches you otherwise wouldn’t need. At $12 million a piece, that amounts to a significant cost avoidance.”
That, for Amos, is the major cost impact of CBM. “There is no overwhelming stack of data saying you will save lots of money” on the maintenance itself, he said. “There is a tendency for the costs of major repair items to be spread out over a longer period of time. The main thing is that you do achieve an increase in availability” and the cost avoidance associated with that.
This, according to the Army posture statement, also enables soldiers “to be more productive, reduce maintenance services and provide leaders the visibility of equipment status needed to implement anticipatory logistics concepts. The current maintenance task paradigm can be changed from preventive to condition based.”
And that is the essence of the transformation being occasioned through the adoption of CBM: A “move from scheduled maintenance in response to accumulation of specified calendar time intervals or operating hours or mileage, to an environment where they can be dynamically scheduled based on the detection of a specified deterioration or operating condition.” ♦
