DAC Lifing
Direct Accumulation Counting — life management of Trent LLPs via Blue Data Thread
What is Direct Accumulation Counting?
Direct Accumulation Counting (DAC) is the Rolls-Royce engine methodology for its modern Trent engines. It is an enhancement to traditional engine Flight Cycle counting for monitoring the lives of Life-Limited Parts (LLPs). Rather than counting one cycle per flight, DAC counts life consumption based on the severity of individual flights and consumes life in fractions of an engine cycle. Life is calculated using the Rolls-Royce DAC Life Usage Calculator (DAC LUC), also known as CoreControl.
Flight-severity based
Life accrues by how severe each flight is, not by flight count.
Fractional cycles
Life is consumed in fractions of a cycle — most flights average under 1 SDC.
Part Feature level
Limits are set per Part Feature, retired before the Defined Safe Cycle Limit.
Standard Duty Cycles (SDC)
Data from each flight is used to calculate LLP life, recorded in units called Standard Duty Cycles (SDC), where 1 SDC equals one engine cycle at the standard lifing profile. Whilst Flight Cycles remain constant, the individual life in SDCs recorded on a flight is variable.
- Life limits are set at Part Feature level rather than component level — Rolls-Royce defines the monitored Part Features in the TLM.
- LLPs are retired before reaching their Defined Safe Cycle Limit (DSCL), independent of how many flights they have flown.
- Part Feature life limits are normalised: each Part Feature has the same limit but accrues life at different rates. The Part Feature driving end-of-life may not be the one with the highest accumulated life.
LLP Life Consumption
LLP life consumed on individual flights is variable and can exceed 1 SDC. The majority of an operation is expected to average less than one SDC per flight, providing overall extended part life compared to traditional Flight Cycle counting. The number of SDCs accrued is based on DAC values — representing flight severity — supplied by the aircraft at the end of each flight.
Factors that increase consumption (> 1 SDC)
- Low levels of derate
- Hot and high departures
- Short warm-up and cool-down times
- Excessive throttle movements
Missing or corrupt data
A default SDC value (defined in the TLM) is applied to all Part Features for that flight.
Pilot training flights
Additional LLP life accrues depending on the number of Touch & Go and Go-Around manoeuvres performed.
DAC LUC System
The DAC LUC system is the executive source of LLP life consumption information for engines using the DAC method. Operators interact with it — manually or automatically via Blue Data Thread (BDT) connectivity — to input the information needed for life usage calculations, and retrieve results back via BDT. LLP life status can also be tracked directly on the User Interface websites and downloaded to support records.
DAC LUC outputs only the current accrued life in SDCs used and remaining. It does not provide life at a historic point in time, or values for individual flights.
Periodically, Rolls-Royce revises the algorithms used to calculate SDC values (coinciding with a TLM up-issue). New algorithms trigger a back-to-birth recalculation of LLP life for all historic flights — this can change current and historic LLP life even though Flight Cycles flown have not changed.
Data Required for DAC Lifing
Three types of data are required. Full technical and project-management support is provided by Rolls-Royce before, during and after EIS, including full training.
DAC values are generated by the Aircraft Condition Monitoring system (Airbus ACMS or Boeing ACMF) and sent from the aircraft by ACARS at the end of each flight, as part of the ACARS End-of-Flight Summary Report (peak-value data for multiple parameters). They are used in DAC LUC to automatically calculate DAC life consumption.
ACARS data supply is set up by the Rolls-Royce Engine Health Monitoring service, which works closely with the DAC Lifing Team under the Rolls-Royce Data & Information department.
On-Boarding an Airline to DAC Lifing
Parallel projects build data exports from the airline maintenance system and capture aircraft performance data supply, both run by Rolls-Royce with its Blue Data Thread partners — culminating in the airline adopting the DAC methodology.
Initiation
EIS −3 to 6 months
Build & Integrate
EIS (Entry into Service)
Validate & Activate
EIS + 12 months
Approval & Adoption
EIS + 15 months
DAC Lifing Service
Transition to DAC Executive Status
Following a minimum of 12 months of data accumulation post-EIS and successful Technical Clearance, an airline is approved by Rolls-Royce to adopt the DAC method. This typically also requires the airline’s DAC standard procedures to be approved by its Local Airworthiness Authority. Formal adoption — DAC Executive Approval — is by way of a written letter of acceptance by the airline, after which it is supported continuously by the DAC Lifing Team.
Lifing Team services (for the life of the TotalCare Agreement)
DAC Systems & Access
Full access is provided to DAC user airlines from initial on-boarding onwards.
DAC LUC CoreControl
Access via the Rolls-Royce Care portal
Intelligent Insight
EoL forecasting — access via the Rolls-Royce Customer Portal
Engine Coverage
Support & Contacts
Non-DAC-Executive operators
A dedicated DAC On-Boarding Project Manager and Implementation Consultant remain your primary contacts until the airline is DAC executive.
DAC-Executive operators
Rolls-Royce Global Service Centre:
Key Terms
Pro Tip
Early engagement between Powerplant engineering and your IT team is critical for successful BDT integration. A minimum of one year of post-EIS data and successful Technical Clearance are required before transition to DAC Executive status.