Dispatch Analysis
Up to four methods. One traceable dataset. Transparent assumptions and calculations.
Purpose and scope: engine-control time-limited dispatch
This tool supports time-limited dispatch (TLD) analysis of engine control systems, particularly full-authority digital engine control (FADEC). TLD assesses operation with detected faults awaiting repair. The tool calculates the fleet-average loss-of-thrust-control (LOTC) rate, compares it with a target, and explores how short-term (ST) and long-term (LT) analysis repair intervals affect that rate.
Methods: Full Markov, first-order and zero-order Markov approximations, and balanced time-weighted average. Inputs can retain individual faults or represent averaged ST/LT conditions.
Single- and two-fault states: this tool models a fully operational state, ST/LT single-fault conditions and LOTC. A second failure causing LOTC is represented by an exit from a single-fault state. Continued operation with two faults is not modeled explicitly. More detailed models can include those states; the repair-rate guideline helps assess when omitting them is reasonable.
Open and closed loops: ARP5107C calls a Markov model open-loop when there is no LOTC-to-full-up feedback. A closed-loop model adds simulated feedback for steady-state analysis. This tool uses closed-loop single-fault formulas; this feedback is mathematical, not an operational recovery from LOTC.
TWA conservatism and acceptability: ARP5107C Section 7.6 (p. 48) states that the time-weighted-average approach gives a conservative LOTC-rate estimate and is an acceptable method for completing the LOTC TLD analysis. This applies to both the original and revised time-fraction coefficients described in the standard.
Scope: engine-control-related LOTC. Model adequacy and permissible dispatch intervals require separate assessment; the calculation does not establish dispatch approval. Source: ARP5107C (September 2018), Sections 1–1.1 (p. 4), 7.1–7.2 (pp. 22–28), 7.2.2–7.2.4 (pp. 31–37) and Appendix G.
Let’s start with your failure and repair data
Please choose the type of data you have. We will explain what to enter before showing your results.
What will you need?
Your hydromechanical failure rate and uncovered fraction X; short-term and long-term repair intervals; flight duration; your fleet-average target; and the failure data for your chosen input type. All rates must be per hour and all durations in hours.
Use occurrence-weighted averages for averaged inputs—not a simple average of fault rates. Individual fault inputs automatically supply the known maximum rates for the repair-rate checks.
Just exploring? Choose a reference example above, then use Load selected example. Examples are loaded only when you request them.
Ready for analysis
Enter fault data or load the illustrative example, results update automatically to show results, derivations, comparison and repair-time sensitivity.
Fleet-average loss of thrust control results
Model comparison
| Method | loss of thrust control rate (per hour) | Signed difference from full Markov | Relative difference (%) |
|---|
Relative differences are measured against the full single-fault-state Markov result, not against an independently verified true rate. The time-weighted average Full-Up contribution may make the methods intentionally non-equivalent.
Input sensitivity analysis
Sensitivity uses 10 equal intervals (11 points). Other inputs stay fixed. Repair intervals must be positive; flight duration may start at zero.
Sensitivity parameter at the target loss rate
Solve for the selected sensitivity input within the entered minimum and maximum. All other inputs stay fixed. A purple marker identifies each target crossing found; this is a calculated analysis interval, not an approved dispatch interval.
Sensitivity values
Repair-rate and failure-rate checks
Detailed calculations
Formula reference
Full Markov · individual Equation 20 or averaged Equation 18
First-order Markov · expansion for the selected state model
Zero-order Markov · Equation 20f
Balanced time-weighted average · Equations 6–9, 11
Model scope, assumptions and limitations
The full model includes each individual short-term or long-term single-fault condition and its direct loss of thrust control exits. Operating conditions with two simultaneous faults are outside this model. Include both channels in the assessed data. Repair rate means one divided by repair interval. The hydromechanical failure rate, X and repair categories must come from your engineering assessment. The combined rate is calculated from these inputs.
The ten-times repair-rate guideline compares repair rate with the maximum relevant failure or transition rate. Approximation accuracy depends on the combined exit rate multiplied by repair interval. A ten-times ratio does not guarantee a particular overall error.
Printed Equation 20a on page 35 omits a repair-interval factor in the denominator. This implementation uses occurrence rate multiplied by repair interval, derived directly from Equation 20. Equation 8 has a label inconsistency; its prose identifies the short-term electronic exit. The repair bounds use Section 7.2.4 and one divided by ten times the maximum transition rate. These interpretations are explained for review; no official correction from the standard’s publisher is claimed.
This tool does not implement no-dispatch states, operational two-fault states, time-since-inspection conversion in Section 8 or multi-engine analysis in Section 9. Review the applicability of the standard, input data and assumptions for your system.