Reliability Tips

  • A friend of mine, who is an opera singer, once said to me: "Surely maintenance is just about oiling equipment." This is the traditional, limited view of maintenance but her point is well made: proper lubrication should never be overlooked in the drive for reliable equipment – just there is more to it than that. Another friend of mine had his petrol lawn mower cease up because of no oil in the engine. Perhaps the opera singer should maintain his mower!
  • One of the mantras of Total Productive Maintenance is: “Cleanliness is next to Godliness.” Keeping equipment clean is the next reliability tip. Indeed for computer equipment, maintaining a good working environment is the only feasible maintenance approach.
  • The US Navy experienced repeated failures on the auxiliary generators on its Phantom F4s until it realized they were overloaded. Therefore we must always operate our equipment within its design envelope and perhaps consider de-rating it to achieve an even longer life where necessary.
  • In the 1960s a study by the CIA (the Chemicals Industry Association not the spy organization) revealed that 30% of pump failures were due to operator error. Therefore proper training is necessary to ensure high reliability for our equipment.
  • We should also design our equipment so it easy to do the right thing and difficult to do the wrong thing. This is sometimes called ‘Fool-proofing’ or ‘Poka-yoke.’
  • Finally, things can change so a reliable piece of equipment now can become suddenly unreliable in the future. Therefore we need a proper management of change procedure to ensure that all changes are considered and authorized before being made.

Did you know...?

  • Functional testing is needed to detect important hidden failures
  • Six Sigma performance means 3.4 defects per million operations.
  • Time-based replacement where there are random failure modes is a waste of time
  • You should record not only that planned maintenance routines have been done but also the condition of the equipment as found and as left
  • If you don't spend about the same amount of money each year on capital refurbishments as the depreciation, then you are just running down the state of your equipments and assets
  • Six Sigma is about reducing variations in performance
  • Lean is about increasing the velocity by which an organisation generates money
  • Failures are cause by equipment deterioration, equipment being wrongly specified in the first place, something changing or a human intervention which went wrong
  • The goal in any manufacturing organisation is to increase the throughput whilst simultaneously reducing both the capital employed and the operating expenses
  • Spending, say, 1% of the value of your assets on capital refurbishment each year means you think they will last 100 years
  • Most organisations have too many spare parts of the wrong type and not enough of the right type
  • Ask a production colleague what is critical and he or she will usually reply – everything
  • If you need to convince your organisation to invest in more spare parts, the Production Director will probably be a good ally
  • Safety first is not only morally right but it is good for business too. Ask Du Pont
  • The simplest solutions are usually the best ones
  • If you don't carry out condition monitoring often enough then unexpected failures will still occur
  • Proper continuous improvement is at the heart of virtually every new tool and technique which you see
  • If you are running an engineering organisation, putting in place renewal schemes, up-grades and managing maintenance then you are doing asset management – even if your job title doesn't mention it
  • Asset management is more than just a fancy name for maintenance
  • Reliability is even more important in a recession than a boom
  • Risk-based maintenance does not mean there will never be a failure

Benchmarking Pitfalls

Being Special

We all pride ourselves on being unique yet most of us buy off the peg clothes in standard sizes. Similarly many organizations convince themselves that they are so special that learning from somewhere else just wouldn’t apply to them. They need to think again – most learning can be applied to other organisations with perhaps a little tailoring to make allowances for true differences.

Just Chasing Cost

Bill Gates didn’t get to number one in computer software by following a cost reduction strategy. Benchmarking to find the cheapest organization is a potential disaster. The cheap organization could be cheap for a very good reason. The comparison should be with a cost-effective organization. Always benchmark a basket of relevant measures and not just one single parameter.

Unfair Comparisons

If I may be permitted to mix metaphors: the old chestnut of not comparing apples with pears is still correct. Comparisons between our organization and another need to be fair in terms of market, conditions, operating context, equipment type, etc.

The Capital / Revenue Split

Just about every organization has different rules for what can be booked to capital and what is a revenue expense. This means that if you are comparing your costs with another organization you need to be careful about the capital / revenue split and how if differs from your situation. Perhaps the safest approach is to find out all capital and revenue costs associated with maintenance and compare the combined figure with yours – that way all costs are being compared.

Internal Politics

The natural place to start benchmarking is internally and this is rightly where many people start. What should be straightforward can be be-devilled by internal politics

Cost Cutting Wrapped up as Benchmarking

There are times when cost-cutting is a vital short-term business tactic but we need to be honest when we carry it out. I once worked with a cement company where the managing director assbled all of his site managers in a conference room. He announced that all sites would be ‘benchmarked’ and the most expensive one closed. You can imagine just how accurate the subsequent site cost figures were! If an expensive site has to be closed then take the Nike approach and just do it.


When benchmarking with external organizations it is vital that confidentiality is maintained otherwise information important to competitive advantage might leak out to competitors. All those taking part in benchmarking need to agree to confidentiality. Groups such as the Benchmarking Network Inc. have developed protocols for achieving this.

No Follow Through

Tennis player making a shotBenchmarking is not just about establishing a position in a league table: we also need to know what needs to be done to move up the league. A simple comparison of metrics needs to be followed through with an analysis of the practices which are driving the metrics. Then people need to be shown what they have to do in order to improve. Just as in tennis we need to hit the ball and then follow through to get a proper shot.


Not linked to Continuous Improvement

Benchmarking is not a one-off, stand-alone activity: it needs to be integrated into the continuous improvement process. Standard internal improvement processes tend to yield important incremental improvements, whereas properly conducted external benchmarking has the capacity to make step changes to performance.

business performance graph


This is the ratio of the time the plant is working at flow sheet rate to the total time available.

Condition-Based Maintenance
The use of information about the condition of equipment in order to decide on the maintenance which is required. 

Consumable Spares
Smaller value spares items such as gaskets, nuts, bolts and thermocouples which have a fairly high rate of turnover and for which likely demand can be predicted with confidence.  Standard techniques can be applied to determine economic order quantity, min/max bin levels or review strategy for holding these items.

Critical Items
Equipment items whose failure will have a significant effect on safety, environmental and / or production factors. 

Downtime/Outage Time
The time period from a trip or loss of output until full output is restored.

Insurance Spares
These items are not expected to be used.  Insurance spares tend to be the larger and more expensive items with long replacement lead times, eg, compressor motors.  Here the investment decisions must balance the cost of money tied up with the probability of requirement and the cost savings they can provide.  The decision making process is complex and Monte Carlo simulation techniques or expert systems can be helpful.

Maintainable Items
Any piece of equipment or part of the plant or its infrastructure which will be subject to condition-based maintenance or planned maintenance/testing on a pre-defined period or after a certain number of units of activity, or planned replacement of life-expired equipment - in order to secure the technical integrity and required availability of the plant.

Having a range of skills which encompasses a mix of traditional craft skills and process operation skills.


Original Equipment Manufacturer.

Plant Spares
These include pumps and motors which have an expected life but are repairable to a greater or lesser extent.  How many of each are required depends on:

  • consequential plant risk from failure,
  • the time to replace or repair item,
  • the policy for stocking of equivalent items elsewhere in the organisation or by a recognised OEM or stockist.

The probability that a piece of equipment will carry out its function over a specified period of time.

Reliability Centred Maintenance
A process used to selected the most cost-effective maintenance activities based on preserving the functioning of equipment in a specified operating environment.

Total Cost of Ownership
Life cycle costing of equipment which takes into account initial purpose cost, running and maintenance costs and finally disposal costs.

Total Productive Maintenance
A process of continuous improvement which is aimed at the identification and elimination of all the causes of minor interruptions and disturbances to output which have a cumulative effect on availability.

For a complete set of maintenance definitions see:
Maintenance Management Terminology
BS EN 13306:2010

Useful Standards & Handbooks

Successful Health & safety Management UK Health & Safety Executive, ISBN 978 0 7176 12765
Criticality Analysis for Maintenance Purposes NORZOK Z-008

Safety Integrity Level IEC 61511-3Asset Management Standard
Publically available standard PAS 55: 2008. ISO 55000 is currently in preparation

Maintenance Management Terminology
BS EN 13306:2010

Petroleum & Natural Gas: Collection and Exchange of Maintenance & Reliability Data for Equipment
ISO 14224 2006

MIL-HDBK-H 108 Sampling Procedures and Tables for Life and Reliability Testing (Based on Exponential Distribution)
This handbook provides procedures and tables based on the exponential distribution for life and reliability testing. It includes definitions required for the use of the life test sampling plans and procedures; general description of life test sampling plans; life tests terminated upon occurrence of pre-assigned number of failures; life tests terminated at pre-assigned time; and sequential life test sampling plans.

MIL-HDBK-189 Reliability Growth Management
This document is designed for both managers and analysts covering everything from simple fundamentals to detailed technical analysis. Included are concepts and principles of reliability growth, advantages of managing reliability growth, and guidelines and procedures used to manage reliability growth. It allows the development of a plan that will aid in developing a final system that meets requirements and lowers the life-cycle cost of the fielded system. The document includes sections on benefits, concepts, engineering analysis, and growth models.

MlL-HDBK-263A Electrostatic Discharge Control Handbook for Protection of Electrical and Electronic Parts, Assemblies and Equipment (Excluding Electrically Initiated Explosive Devices)
This handbook provides guidance for developing, implementing and monitoring an ESD control program for electronic parts, assemblies and equipment in accordance with the requirements of MIL-STD-1686. This document includes definitions, causes and effects (including failure mechanisms), charge sources, list and category of electrostatic-sensitive devices by part type, testing, application information, considerations, and protective networks. The specific guidance provided is supplemented by technical data contained in the appendices. Table I provides a cross-reference listing of MIL-STD-1686 requirements, MIL-HDBK-263 guidance, and MIL-HDBK-263 supplementary technical data.

MIL-STD-690C Failure Rate Sampling Plans and Procedures
This standard provides procedures for failure rate qualification, sampling plans for establishing and maintaining failure rate levels at selected confidence levels, and lot conformance inspection procedures associated with failure rate testing for the purpose of direct reference in appropriate military electronic parts established reliability (ER) specifications. Figures and tables throughout this standard are based on exponential distribution.

MIL-STD-721C Definition of Terms for Reliability and Maintainability
This standard defines terms and definitions used most frequently in specifying Reliability and Maintainability (R & M). Provides a common definition for the Department of Defense and defense contractors.

MIL-STD-756B Reliability Modelling and Prediction
This standard establishes uniform procedures and ground rules for the generating mission reliability and basic reliability models and predictions for electronic, electrical, electromechanical, mechanical, and ordnance systems and equipments. Model complexity may range from a complete system to the simplest subdivision of a system. It details the methods for determining service use (life cycle), creation of the reliability block diagram, construction of the mathematical model for computing the item reliability. Some simple explanations on the applicability and suitability of the various prediction sources and methods are included.

MIL-STD-1629A Procedures for Performing a Failure Mode, Effects, and Criticality Analysis
This document shows how to perform a Failure Mode, Effects, and Criticality Analysis (FMECA). It establishes requirements and procedures for performing a FMECA to systematically evaluate and document, by item failure mode analysis, the potential impact of each functional or hardware failure on mission success, personnel and system safety, system performance, maintainability, and maintenance requirements. Each potential failure is ranked by the severity of its effect in order that appropriate corrective actions may be taken to eliminate or control the high risk items. It details the functional block diagram modelling method, defines severity classification and criticality numbers. It provides sample formats for a FMEA, criticality analysis, FMEA and criticality analysis maintainability information sheet, and damage mode and effects analysis sheet. The document also provides several examples.

MIL-STD-2074 Failure Classification for Reliability Testing
This document establishes criteria for classification of failures occurring during reliability testing. This classification into relevant or non-relevant categories allows the proper generation of MTBF reports. This document applies to any reliability test, including, but not limited to, tests performed in accordance with MIL-STD-781.

MIL-STD-2155 Failure Reporting, Analysis and Corrective Action System (FRACAS)
This document establishes uniform requirements and criteria for a Failure Reporting, Analysis, and Corrective Action System (FRACAS) to implement the FRACAS requirement of MIL-STD-785.

MIL-STD-470B Maintainability Program Requirements for Systems and Equipment
This document includes application requirements, tailorable maintainability program tasks, and an appendix with an application matrix and guidance and rationale for task selection. The topics covered are program surveillance and control, design and analysis, modeling, allocations, predictions, failure mode and effects analysis, and maintainability design criteria. Each task item includes a purpose, task description, and details to be specified. Software maintainability is not covered by this document.

MIL-STD-471A Maintainability Verification/Demonstration/Evaluation
This document provides procedures and test methods for verification, demonstration, and evaluation of qualitative and quantitative maintainability requirements. It also provides for qualitative assessment of various integrated logistic support factors related to and impacting the achievement of maintainability parameters and item downtime, e.g. technical manuals, personnel, tools and test equipment, maintenance concepts and provisioning.

MIL-HDBK-472 Maintainability Prediction
This document is to familiarize project managers and design engineers with maintainability prediction procedures. It provides the analytic foundation and application details of five prediction methods. Each procedure details applicability, point of application, basic parameters of measure, information required correlation, and cautionary notes. The highlights of each maintainability prediction procedure are presented in a clear and intelligible manner and include useful supplementary information applicable to specific procedures. Maintainability Prediction Procedures I and III are applicable solely to electronic systems and equipments. Procedures II and IV can be used for all systems and equipments. In applying Procedure II to non-electronic equipments the appropriate task times must be estimated. Procedure V can be used to predict maintainability parameters of avionics, ground and shipboard electronics at the organizational, intermediate and depot levels of maintenance.

DOD-HDBK-791 Maintainability Design Techniques
This handbook supplies information on incorporating maintainability into Army materiel design. It defines maintainability and discusses its importance, quantitative measurement, and incorporation into the design process. Other subjects discussed in detail cover simplification, standardization and interchangeability, accessibility, modularization, identification and labeling, testability and diagnostic techniques, preventive maintenance, human factors, and environmental factors as they relate to maintainability.

MIL-STD-1591 On Aircraft, Fault Diagnosis, Subsystems, Analysis/Synthesis of
This document establishes uniform criteria for conducting trade studies to determine the optimal design for an on-aircraft fault diagnosis/isolation system. This document is applicable where a selection can be made between such alternatives as central computer controlled on-board centrally polled built-in test equipment (BITE), decentralized BITE, detached Aerospace Ground Equipment (AGE), etc., or combinations of the preceding. The fault diagnosis/isolation systems of interest are those used to diagnose/isolate faults at the flight line (organizational) level of maintenance. This document also provides a cost model and a maintainability labor power model.

MIL-STD-1843 Reliability-Centered Maintenance for Aircraft, Engines and Equipment This document, which is based on the Airline/Manufacturer Maintenance Program Planning Document MSG-3, outlines the procedures for developing preventive maintenance requirements through the use of Reliability-Centered Maintenance Analysis (RCMA) for Air Force aircraft and engine systems, aircraft and engine structures and equipment, including peculiar and common Support Equipment (SE) Communications and Electronics (C-E) equipment, vehicles, weapons and other similar equipment items.

MIL-STD-2084 Maintainability of Avionic & Electronic Systems and Equipment
This document covers the common maintainability design requirements to be used in military specifications for avionic and electronic systems and equipment.

MIL-STD-2165A Testability Programs for Electronic Systems & Equipment
This document is intended to prescribe a systematic approach for establishing and conducting a testability program. It describes a uniform approach to testability program planning, establishment of diagnostic concepts and testability (including BIT) requirements, testability and test design and assessment, and requirements for conducting testability program reviews. Relevant tasks in this document are to be applied during the conceptual phase, demonstration and validation phases, full-scale development phase and production phase of the acquisition process.

DOD-STD-1701 Hardware Diagnostic Test System Requirements
This document establishes the general procedures, terms and conditions governing the preparation and completion of a hardware diagnostic test system.

MIL-STD-2173 Reliability-Centered Maintenance Requirements for Naval Aircraft, Weapons Systems and Support Equipment
This document is used to provide procedures for a Reliability-Centered Maintenance analysis for naval aircraft, weapons systems, and support equipment. This document is used during development of new systems and equipment, and by analysts and auditors within the Naval Air Systems Command for determining preventive maintenance requirements and developing age exploration requirements. The document can also be used to update the initial reliability-centered maintenance analysis and analyze newly discovered failure modes.

MIL-STD-001591A Subsystem Analysis/Synthesis of Command, Control & Communication (C3) System Component Fault Diagnosis
This document establishes uniform criteria for conducting trade studies to determine the optimal design for command, control and communication system and component fault diagnosis/isolation subsystems, These types of systems are referred to as Fault Identification & Test Subsystems (FITS). FITS include the hardware and/or software necessary for the detection and isolation of failures.

IEC 60300 - 3 – 12/CVD  Dependability Management – Applications guide for Integrated Logistics support
This document establishes Integrated Logistics Support as a management method by which all of the logistic support services required by a user can be brought together in a structured way and in harmony with a product at optimum cost.

© 2021 Red Wheel Solutions Limited. All rights reserved