Reliability Assessment

Analysis

In order to run a Reliability Assessment, it is necessary to access FRACAS > Reliability Assessment. There are different types of assessments that can be performed:

  • Assessment at Part Level: Only parts of the aircraft are analyzed (e.g. an actuator)

  • Assessment at System Level: A whole system of the aircraft is analyzed (e.g. electrical system)

  • Assessment at A/C Level: An entire aircraft is analyzed (all components)

  • Assessment at Fleet Level: Fleets are analyzed

Moreover, the user can choose to run a standard reliability assessment or a drill-down assessment, where the reliability of each customer/fleet is broken down.

An assessment is described by a title, a set of conditions and some settings. The conditions that can be defined are:

  • Fleet

  • From/to A/C SN

  • ATA chapter

  • Aircraft Type

  • PN (part)

Entering more than one of these fields will imply an AND condition. When pressing “Add conditions”, the user can enter another set of conditions which will be unified to the previous ones (OR). “Delete last condition” can be used to delete the last entered condition.

Then, the settings that can be modified are:

  • Months Moving Average: Number of months to consider when calculating the number of defects and flying hours

  • Total MTBF?: If true, Months Moving Average is not applicable. The entire history of defects and flying hours is considered

  • Months Ago: Number of months ago up to which the reliability assessment is computed

  • Factor of DV for Open defects: A factor from 0 to 1, which indicates the percentage of open defects (with no “Damage Effect”) that are considered to be DV (Defect Verified)

  • Extrapolation Type: When not having flying hours data, an extrapolation has to be applied. Three types of extrapolation are available:

    • 1: Linear with the first and last point of flying hours history

    • 2: Linear with the last two points of flying hours history

    • 3: Quadratic with the last points of the curve

../_images/fracas_assessment.PNG

When pressing compute reliability assessment, the computations start and a progressbar indicates their state.

../_images/fracas_assessment2.PNG

Warning

When choosing the same conditions and settings of a reliability assessment already saved in the database, the previous reliability assessment is deleted.

Charts

When the analysis is finished, the user is prompted to see the result chart in the page FRACAS > Statistics and graphics > Reliability Assessment. The user can choose any calculated assessment to be displayed. Then, the user can navigate through all the calculated parts, aircraft, fleets…

../_images/fracas_assessment3.PNG

As it can be seen in the image above, several series are displayed in the Reliability Assessment:

  • The flying hours of all the aicraft affected by the conditions of the assessment are displayed in bars

  • The other series are line-series:

    • MTBF: Mean Time Between Failures

    \[MTBF = \frac{\sum_{i_{aircraft}} FH_{i_{aircraft}}}{\#DV + \#DSR + \#RDV + f \cdot \#Open}\]

    • MTBUR: Mean Time Between Unscheduled Removals

    \[\begin{split}\small MTBUR = \frac{\sum_{i_{aircraft}} FH_{i_{aircraft}}}{\#DV + \#DSR + \#RDV + \#ND + \#NFF \\ + \#RNFF + \#RDSR + f \cdot \#Open}\end{split}\]

    • MTBCF: Mean Time Between Critical Failures. It only counts the defects which the user has marked as critical

    • PMTBF: Predicted MTBF given by the supplier

    • GMTBF: Guaranteed MTBF given by the supplier

As it can be observed from the above formulas, the MTBUR is always lower than the MTBF.

Warning

The greyed box in the chart indicates that, during this period, no defect occurred. Hence, both the MTBF and MTBUR are set to be equal to the number of flying hours.

Warning

To calculate the MTBF and MTBUR, only the type of defects included in the above formula are considered.

Finally, Corrective Actions meetings (if any) are also displayed in the chart. The settings and conditions of the reliability assessment are also indicated on the right-hand side of the chart. The MTTR and availability of the selected part are also displayed.

A report of the charts of a given reliability assessment can be also printed in PDF by pressing the “Print” button.