Hydraulics monitoring and troubleshooting might be getting easier. Revima and its Flightwatching unit have monitored hydraulic systems on about 200 aircraft to date. Flightwatching chief Jean-Philippe Beaujard says it is still too early to provide reliable information on potential benefits. “We are mainly guided by our customer needs,” Beaujard notes. “When they have an issue on the hydraulic system, we put in place the best monitoring we can get from their fleet without modifying the aircraft configuration. We get the best out of what they already have. The monitoring set-up provides a high degree of reliability, which is better than that of the BITE [Built-In Test Equipment] fault messages alone.”
Revima collects key parameters from sensors related to hydraulics systems in avionic computers, either in real time during flight or through a post-flight analysis of data stored on recorders like flight data recorders or quick access recorders. “The collected parameters are then analyzed and compared with normalized values depending on flight phase,” Beuajard says. “Abnormal behaviors trigger an alert that sends automatic email to maintenance control.”
Both Airbus and Boeing aircraft now transmit BITE failure messages after either the hydraulic system or a component that consumes hydraulic power detects a fault during flight. This technique is, in a sense, predictive because it transmits messages to maintenance control before a cockpit alert appears to pilots. The BITE fault message enables troubleshooting to begin before a warning appears in the cockpit.
But the Revima exec says that, for ATA 29 hydraulic components, troubleshooting procedures do not necessarily lead to identification of root causes. “The failure scenario is difficult to replicate on the ground. Hydraulic faults can depend on vibration conditions, aircraft attitude such as pitch and roll, as well as outside temperatures and pressures.” Revima’s predictive maintenance approach is thus a complement to BITE messages. “Our algorithms focus on root causes of failures.”
Beaujard says all parameters related to hydraulic systems can be important for predictive maintenance. One example is hydraulic servicing data. This data provides the most precise information for ramp staff before departure, and measurements on ground provide a reference point useful in detecting abnormal behaviors.
Revima offers a hydraulic dashboard providing real-time feedback to maintenance control while aircraft are either on the ground or flying. “Results are easy to understand because the dashboard represents what maintenance staff are used to seeing when opening hydraulic servicing hatches,” Beaujard notes.
This dashboard can also measure hydraulic reservoir levels more precisely than is possible on aircraft. “Hydraulic reservoir level indicators on aircraft are provided by gauges that sometimes stick, or the needle indicator is subject to friction and gives an erroneous value,” Beaujard says. “By reading digital values coming from avionics computers, our monitoring is a much more reliable source of information.”
Non-sensed parameters are also important. For example, “hydraulic performance is an important non- sensed parameter that provides key information,” Beaujard says.