Legacy Aircraft Mode

Legacy Aircraft Mode supports representation of aircraft programs where actual retirements and attritions are known, or estimated for the near future, or where retirements and attritions do not follow standard, consistent patterns. It allows retirements and attritions to be specified in the Program Profile input sector in an annual table and overrides the normal mechanisms that OSCAM has for retirement and attrition. The Introduction Profile should be used in the normal way for aircraft introductions at the start of the program life. Use the Cost Deferral option in the Program Profile to only capture costs from a specified year onwards. While Legacy Aircraft Mode mainly involves inputs in the Program Profile, it can also impact logic for O/I maintenance, depot maintenance and modernizations.

Entering aircraft introductions and normal life expectancy

Specify aircraft introductions as normal, from the start year of the program. OSCAM will represent the full life of the program from the introduction of the first aircraft to the retirement of the last. You can exclude past costs from the analysis by using the  Defer Cost option to specify the year that you want to collect costs from. You still need enter the normal life expectancy of the aircraft. While this will not affect the retirement dates of Aircraft in Legacy Aircraft Mode, it does help to keep track of aircraft ages which can impact some maintenance costs if aging factors are in use for detailed O-Level and I-Level Maintenance.

Aircraft introductions in the Program Profile with Defer Cost option selected

 Aircraft Introductions tab in the Program Profile sector

Legacy Aircraft Mode tab

The Program Profile Aircraft tab has a "Legacy Aircraft Mode" sub-tab. Select the tab and enable Legacy Aircraft Mode with the check box. Once this is done the Legacy Aircraft Mode table will be enabled.

On a year by year basis, use the table to enter number of retirements and attritions. Annual diagnostic information is updated on cumulative totals and number of aircraft in the program at the start and end of each year.

Service Life Extension Program (SLEP) costs can also be specified on an annual basis. However, unlike Modernization in Continuing System Improvements, this is just a cost and does not take aircraft out of service for any period of time.

The diagnostic text to the right of the table provides information to help configure the table. It shows any discrepancies between number of aircraft introduced and number leaving service.

Legacy Aircraft Mode tab

 Legacy Aircraft Mode input tab

The screenshot above shows the number of aircraft retiring being entered on a year by year basis, starting in 2019 and ending in 2028 (not shown). The table also includes an intermittent pattern of attrition starting from the year first aircraft were introduced. This can use historical information where known, and estimates for future years. Service Life Extension (SLEP) costs are entered for the years 2021 to 2024.

The remainder of the columns in the table provide diagnostics information showing the number of aircraft in the program at the start of the year, cumulative retirements up to and including that year, cumulative attritions, cumulative aircraft no longer in service, and the number of aircraft in the program at the end of the year.

The diagnostic information to the right of the table provides information on the number of aircraft introduced, the total number of aircraft specified as retiring, the total number of attritions, any discrepancy between introductions and aircraft leaving service, the year that the last aircraft leaves service, and the total Service Life Extension costs.

In the example, the number of aircraft introductions and number leaving service match, as shown by the green 0 in the diagnostic text for the difference between the two. If there is a discrepancy then this will be shown in red and warning text will be displayed. It will not be possible to run a simulation until any discrepancies are resolved.

Legacy Aircraft Mode diagnostic warning message

 Legacy Aircraft Mode diagnostic with warning message

Impacts of Legacy Aircraft Mode on other Program Profile inputs

When Legacy Aircraft Mode is in use, all other mechanisms in OSCAM for retirement and attrition are switched off so that only the retirements and attritions shown in the Legacy Aircraft Mode table will be used. There will be no age-based retirements, no flying hours-based retirements, no early retirements due to emergency repair, and no flying hours or percentage-based attritions. Life extensions in Modernization will not affect retirements.

Retirements and attritions occur at the end of the year (actually the start of the following year for logic and reporting purposes). Aircraft will be retired in order of age, while attrition will be spread across the range of aircraft ages.

The impacts of Legacy Aircraft Mode mean that some Program Profile inputs will be disabled. Aircraft will only enter service at the start of a year, the Aircraft Flying Hours Life input is disabled, and the Service End Year input is disabled. There is an Aircraft Life Expectancy input, but it is only used to determine the baseline life in years for maintenance action aging factors. The OpTempo tab will have its attrition inputs disabled.

Aircraft Introductions tab when Legacy Aircraft Mode is enabled

 Aircraft Introductions tab in the Program Profile sector with Legacy Mode enabled

OpTempo tab when Legacy Aircraft Mode is enabled

 OpTempo tab in the Program Profile sector with Legacy Mode enabled

Populating other inputs when using Legacy Aircraft Mode

The rest of the inputs in OSCAM will work largely the same in Legacy Aircraft Mode as they would for a standard run. There are a few differences in the model logic, as shown below.

Impacts of Legacy Aircraft Mode on O/I Maintenance

The Aircraft Life Expectancy is defined in the Program Profile which may be extended by Modernization life extensions to generate the Extended Life Expectancy. In standard mode OSCAM would retire aircraft if/when they reached their Extended Life Expectancy, but in Legacy Aircraft Mode the retirements occur as specified in the Legacy Aircraft Mode table so aircraft could exceed this age.

The Maintenance sector has Aging Action Rate Factors for O-Level and I-Level detailed aircraft and engine maintenance. These factors can impact action rates as aircraft age. The Extended Life Expectancy in the Program Profile represents the 100% of life point in the Aging Action Rate Factor tables. Since aircraft age does not trigger retirement it is possible that aircraft can exceed the Extended Life Expectancy age and so exceed this 100% point. The Aging Action Rate Factor scale now exceeds 100%, allowing factors to be specified in the table up to 120% of aircraft life. After 120% the simulation model uses linear extrapolation for the factor. If the Equation Format is used instead of the Table Format then the equation just uses the aircraft age (in years), which can exceed the Extended Life Expectancy.

Aging Action Rate Factor extended to 120% of aircraft life expectancy

 Aging Action Rate Factor graph specified up to 120% of extended aircraft life.

Impacts of Legacy Aircraft Mode on Depot Maintenance

Any PDM retirement cut-off period will continue to be applied for aircraft scheduled to retire in Legacy Aircraft Mode. OSCAM will use the retirement dates specified in the Legacy Aircraft Mode table rather than any age-related or flying hours related retirement.

A Emergency Repair retirement cut-off period will be applied for aircraft scheduled to retire in Legacy Aircraft Mode, but will just prevent the ER from occurring. It will not cause aircraft to be retired early and aircraft will continue to fly until retirement.

 PDM and Emergency Repair retirement cut-offs will not be applied to aircraft that are scheduled for attrition (aircraft to be attrited will be selected from the available fleet, not aircraft in PDMs, Emergency Repair, or Modernization). Despite the fact that OSCAM knows the attrition date from the Legacy Aircraft Mode table, this would not normally be something that could be anticipated in the real world and so a cut-off for PDMs or Emergency Repairs would not be applied. Attrition may be delayed to later than schedules if no aircraft are available (this is very unlikely to happen in most normal data records). However, aircraft will not enter a PDM, Emergency Repair, or Modernization if it is due to finish after the last aircraft is scheduled to leave service (retirement or attrition); i.e. the program will not be extended to wait for aircraft to return from the depot.

Impact of Legacy Aircraft Mode on Continuing System Improvements

Normally Modernization programs cannot be scheduled to occur after the retirement age of an aircraft. However, in Legacy Aircraft Mode aircraft introduced in the same year may retire at different ages so no validation is applied in the user interface for the start year of a modernization program.

Aircraft will only enter a Modernization program if they will finish it before their scheduled retirement date. This is not the case for attrited aircraft – any aircraft in a Modernization program will not be eligible for attrition. No aircraft will enter a Modernization Program if it would finish after the last aircraft is scheduled to leave service (retirement or attrition), so as to ensure that the program does not exceed the specified end date.

Aircraft Life Extension inputs will increase the extended service life value, but this will not impact the age that an aircraft retires it. It will change the age represented by 100% in the Maintenance Aging Action Rate tables. Flying Hours Life Increase inputs have no impact in Legacy Aircraft Mode

Output 5.1.3 Service Life Extension Program Cost is a Legacy Aircraft Mode only cost which is populated in the Program Profile.

Impact of Legacy Aircraft Mode on the Unmanned Air Systems sector

Ground stations will be retired in line with aircraft retirements, e.g. if there are 5 aircraft per ground station then 1 ground station will be retired for every 5 aircraft retirements. Aircraft attrition will not be used for ground station retirement, instead the ground station will be retained (but might not be used) until all aircraft have retired.

The Ground Station Aging Action Rate factor uses the Aircraft Extended Life as the age representing 100%, but aircraft (and ground stations) can exceed this. The factor table displays up to 120%, beyond that the simulation model will use linear interpolation. The Equation Format uses the age of aircraft (in years) and so the age value is used directly by the equation.