3.6.2 Ground Segment
The ground station performs a number of functions. Upon receiving the data cartridge from the aircraft, it generates a maintenance report containing all parameter exceedances encountered during the .ight, accompanied by their corrective actions. It also keeps track of load cycles, and alerts the user if a
3.6. M’ARMS AND EUROARMS

component has reached its safe life limit.
On the vibration acquisition of each component a number of indicators are calculated. These are then evaluated against thresholds to determine if a fault is present on the associated component. Indicator threshold breaches are added to the maintenance report, accompanied with the maintenance actions for the detected fault types.
While some thresholds are globally .xed, most are individual to each aircraft. These thresholds are set based on a training period, where the normal state location and dispersion for each indicator is identi.ed. Following major overhauls, aircraft individual thresholds must be reset, as overhauls changes the vibration signature of the transmission system.

3.6.3 Decision Flow
Under normal circumstances, the operator is able to determine if a fault is present on a helicopter by evaluating the ground station output. When in doubt, the operator submits a defect report to Eurocopter customer support. This is normally done by fax / email, with screenshots of the a.ected indi-cator plots attached. An expert evaluation is then returned to the operator (Fig.
3.6).

In addition to this problem driven data .ow, digital HUMS data is sub-mitted to Eurocopter on more or less regular intervals. This is done by sending data backup tapes in the mail. This approach is however too slow to use in support cases, as the backup tapes can take several days before reaching Eurocopter.

3.6.4 Improvement Potential
This study limits itself to address surveillance of the transmission system between the engines and the rotors, as well as any IT-related problems re-lated to this task. Monitoring of engines and rotors are the topic of other studies, and will therefore not be treated here. Any problems related to the implementation of traditional and well proven usage functions, like parame-ter exceedance warnings, are considered to be more a development / quality assurance nature, and are thus also excluded from this study.

3.6. M’ARMS AND EUROARMS
This section suggests a number of possible improvements of the ARMS solutions. The overall aims for these propositions are to:
.
Reduce false alarm rates

.
Increase detection rates

.
Reduce operator workload

Only methods related to vibration monitoring, or methods replacing ex-isting vibration monitoring techniques are considered. Some of these propo-sitions are outside the scope of this study, in the sense that they can not be implemented and tested during the assigned time-frame. They are none the less included for future reference, and as recommended topics for future studies.
　
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