Aircraft vs. Component vs. Engine Reliability: Data Used & Outputs

Date

July 25, 2025

Time

3 min read

Data in Aviation Maintenance Decision-Making

Technical Records

Aircraft Tech Log: Information Covered, Impact, and Common Findings

Originally published on Linkedin — *Originally published on* *Linkedin*

Reliability, in simple terms, is calculated by dividing the number of failures by the total exposure within a certain time window. For example, if there were 10 failures of a fuel heat exchanger over the course of a year, that becomes the basis for the reliability calculation.

Reliability analysis differs depending on whether you’re looking at the aircraft, components, or engines, even though the purpose is the same: identifying recurring issues and preventing them.

Reliability Data Sources

For aircraft, reliability engineers rely on reports from pilots and maintenance teams, which highlight malfunctions or operational issues. In components, the focus is typically on the number of unscheduled removals. For engines, sensor data plays a much larger role. Parameters like exhaust gas temperature and vibration are used to detect trends or early warning signs before failures occur.

Metrics	Aircraft Reliability	Component Reliability	Engine Reliability
Data Source	MAREP, PIREP, Technical delay reports	Removal records, component logbooks, Component Shop Report	Aircraft & engine flight data, LLP records, tech logs, etc
Data Used	FH/FC, TSN/CSN, Technical Delay Rate, Description & Rectification, Dispatch Reliability, PIREP & MAREP Description, Number & Rate, later codified by ATA Chapter (up to 6 codes)	Unscheduled Removal Number & Rate => MTBUR (Mean Time Between Unscheduled Removals), No Fault Found (NFF) rate	FH/FC (for calculating LLP usage), performance trends (temperature, vibration, oil consumption)

Outputs, Questions Answered & Follow Up Actions

At its core, the purpose of reliability analysis is to identify which parts, ATA chapters, or systems are repeatedly causing issues and whether there’s a deeper root cause that requires attention. This information is typically presented in regular reliability reports. When specific thresholds are exceeded, alerts are triggered—such as Aircraft Follow-On Notices or Component Alert Notices. The exact naming varies by operator. These reports indicate if certain components, ATA chapters, or system failures have occurred more frequently than acceptable limits (which also differ between operators). They also provide root cause insights and recommend short-term and long-term actions.

The findings can impact other departments as well. For example, procurement may adjust spare part orders based on flagged part numbers. Planning teams might revise maintenance schedules to avoid multiple major events occurring in the same timeframe, helping manage cost and operational impact.

Metrics	Aircraft Reliability	Component Reliability	Engine Reliability
Output	Periodic Reliability Report, Aircraft Follow On-Notice (or equivalents), Recurrent Defect Report	Periodic Reliability Report, Component Alert Notice (or equivalents)	Periodic Reliability Report, Engine Staggering Plan
Question Answered	Which ATA chapters are driving repeat delays? Which systems show up most often in MAREP/PIREP reports? Is there an underlying pattern? What follow-up actions are needed—interim and long-term?	Which parts are hitting unscheduled removals too early? Any common root causes across failures? Does this affect how we stock or rotate components?	Which engines are due for removal based on trend data? Can removals be staggered to avoid cost spikes from overlapping shop visits? Do we have enough spares on hand—or are we risking expensive short-term leases or AOG events?
Follow Up Action	Recommend inspections, checks, and short/long term solution Search similar issues from past case data (such as via MyBoeingFleet)	Adjusted task intervals Preventive replacement strategy Change spares stock strategy for high-failure items Cross-check for similar cases of that P/N Minimum Stock Level Calculation	Borescope inspections Removal schedule and staggering plan Flag the engine for deeper evaluation if say there are anomalies Recommend inspections, checks, or other troubleshooting methods

Why Reliability Isn’t One-Size-Fits-All

Ultimately, reliability metrics require continuous analysis, usually tracked month by month using a rolling window. Reliability values are not absolute—there is no single “correct” number. They are often influenced by financial considerations, operational goals, and maintenance strategies. What’s considered acceptable in one context may not be in another.

Results could also even vary across different engineers. Engineers are still responsible for verifying input data, what should be included or excluded, identify outliers and interpret results in context to avoid drawing the wrong conclusions from raw trends. This is why domain expertise remains essential. Experience helps determine which signals are operationally relevant and which can be disregarded.

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