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[[https://www.emerald.com/insight/content/doi/10.1108/AEAT-01-2018-0037/full/html|
Piston-electric propulsion system as reliable alternative for classic and nonconventional piston engine configurations]]

Abstract

Purpose

The purpose of this paper is to define reliability requirements to be imposed on electric engines to assure similar or higher value of mean time between failures (MTBF) for mixed piston-electric propulsion configurations when compared to classic and unconventional piston engine configurations.
Design/methodology/approach

Reliability estimation was done using mathematical model of safety of light aircraft commercial operations. The model was developed on the basis of Federal Aviation Administration and National Transport Safety Board data. The analysis was conducted for numerous piston and electric configurations. It allowed comparison of selected solutions and definition of relation between electric engine MTBF and MTBF calculated for entire mixed piston-electric propulsion system.

Findings

**It was found that, from reliability point of view, mixed piston-electric engine propulsion is attractive alternative for classic single- and twin-piston configuration. It would allow to at least doubling of MTBF for propulsion without increase of operational cost.**

Practical implications

Rationale behind exploiting electric propulsion in aviation is provided. Relation between electric engine reliability and entire propulsion reliability was identified and defined. Minimum requirements concerning MTBF value for electric engine application in aviation was assessed. Conclusions from this study can be used for definition of requirements for new aircraft and by the regulatory authorities.

Originality/value

Originality consists in use of real accident statistics included in mathematical model of safety for assessment of MTBF for various classic and novel piston and piston-electric engine configurations of light aircraft. Output from the study can be exploited by the industry.


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[[https://www.linkedin.com/pulse/understanding-mttf-mtbf-mttd-mttr-aircraft-analysis-sandirajah/|
 Understanding MTTF, MTBF, MTTD, and MTTR in Aircraft Maintenance Engineering: A Comprehensive Analysis ]]



In the field of aircraft maintenance engineering, several metrics are used to assess the reliability, availability, and performance of aircraft systems. Mean Time to Failure (MTTF), Mean Time Between Failures (MTBF), Mean Time to Detect (MTTD), and Mean Time to Repair (MTTR) are key metrics that aid in analyzing system behavior, optimizing maintenance processes, and ensuring efficient aircraft operations. This article provides a detailed exploration of these metrics, their calculations, formulas, and their significance in aircraft maintenance engineering.


1. Mean Time to Failure (MTTF):

MTTF refers to the average time between failures of a system or component assuming that repairs are not carried out, and the system is allowed to operate until it fails completely. MTTF is commonly used for non-repairable systems and is expressed in hours.

Calculating MTTF:

MTTF can be calculated using the following formula:

MTTF = Total Operating Time / Number of Failures

For example, if an aircraft component has been in operation for a total of 1,000 hours and has experienced two failures during that time, the MTTF can be calculated as:

MTTF = 1,000 hours / 2 failures

MTTF = 500 hours

In this case, the MTTF of the component is 500 hours, indicating that, on average, the component is expected to fail after 500 hours of operation.

2. Mean Time Between Failures (MTBF):

MTBF is a measure of the average time between two consecutive failures of a system or component, considering both repair and downtime. MTBF is typically used for repairable systems and is expressed in hours.

Calculating MTBF:

MTBF can be calculated using the following formula:

MTBF = Total Operating Time / Number of Failures

For instance, if an aircraft system has been in operation for a total of 2,000 hours and has experienced three failures during that time, the MTBF can be calculated as:

MTBF = 2,000 hours / 3 failures

MTBF ≈ 666.67 hours

In this example, the MTBF of the system is approximately 666.67 hours, suggesting that, on average, the system can operate for 666.67 hours before experiencing a failure.

3. Mean Time to Detect (MTTD):

MTTD represents the average time it takes to detect a failure or anomaly in a system. It includes the time from when a failure occurs to when it is identified or detected.

Calculating MTTD:

MTTD is typically determined based on historical data or through simulations. It can be calculated by analyzing the time stamps of failure detection in the system or component.

4. Mean Time to Repair (MTTR):

MTTR denotes the average time required to repair a failed system or component and restore it to full operational status. MTTR includes diagnosis, repair, testing, and any other necessary activities.

Calculating MTTR:

MTTR can be calculated using the following formula:

MTTR = Total Repair Time / Number of Failures

For example, if a specific aircraft system has experienced five failures and the total time taken to repair these failures is 20 hours, the MTTR can be calculated as:

MTTR = 20 hours / 5 failures

MTTR = 4 hours per failure

In this case, the MTTR of the system is 4 hours per failure, indicating that it takes an average of 4 hours to repair the system after each failure.

Significance of MTTF, MTBF, MTTD, and MTTR in Aircraft Maintenance Engineering:

These metrics play crucial roles in aircraft maintenance engineering:

- MTTF and MTBF help assess system reliability, identify areas for improvement, and optimize maintenance strategies.

- MTTD enables timely detection of failures, minimizing potential safety risks and preventing cascading system failures.

- MTTR is essential for minimizing aircraft downtime, ensuring efficient repairs, and maximizing system availability.

By continuously monitoring and analyzing these metrics, maintenance professionals can implement preventive and predictive maintenance approaches, leading to enhanced system reliability, reduced operational disruptions, improved safety, and optimized resource allocation.

MTTF, MTBF, MTTD, and MTTR are essential metrics in aircraft maintenance engineering for assessing system dependability, availability, and maintenance efficiency. By combining these metrics, they provide valuable insights into system behavior, guide maintenance practices, and help optimize aircraft operations. Proactively addressing failures, minimizing downtime, and ensuring safe and reliable aircraft systems can be achieved by regularly calculating and monitoring these metrics.