AeE 418: Human Systems Engineering

Reliability Engineering

evident in regulatory mandates and prescribed standards, through Reliability Programs and Continuing Airworthiness Mgt.

CAAP’s PCAR Part 9 - AOC

(b) The Authority will require an operator to include a reliability program when the Authority determines that such a reliability program is necessary. When such a determination is made by the Authority the operator shall provide such procedures and information in the operator's maintenance control manual

(c) Each operator shall ensure that each aircraft is maintained in accordance with the operator's aircraft approved maintenance program as required by Subpart 9.4.1.3, which shall include:

(1) Maintenance tasks and the intervals in which these are to be performed, taking into account the anticipated utilization of the aircraft:

(2) When applicable, a continuing structural integrity program,

(3) Procedures for changing or deviating from subparagraphs (c)(1) and (c)(2) and

(4) When applicable, condition monitoring and reliability program, descriptions for aircraft systems, components, and power-plants (for helicopters: power

CAAP’s PCAR Part 9 - AOC

9.4.1.2

MAINTENANCE RESPONSIBILITY

(a) Each operator shall ensure the airworthiness of the aircraft and the serviceability of both operational and emergency equipment by

(1) Assuring the accomplishment of preflight inspections;

(2) Assuring the correction of any defect and/or damage affecting safe operation of an aircraft to an approved standard, taking into account the MEL and CDL if available for the aircraft type;

(3) Assuring the accomplishment of all maintenance in accordance with the approved operator's aircraft maintenance program:

(4) The analysis of the effectiveness of the operator's approved aircraft maintenance program;

(5) Assuring the accomplishment of any operational directive airworthiness directive

1. Dispatch Reliability

2. Systems reliability

3. Component Reliability

4. Powerplant Reliability

4 Reliability Areas/Scope

Dispatch Reliability

the percentage of total flights that departed on-time within a specified time of the scheduled departure times

Dispatch Reliability

"specified time" margin is first defined - industry practice uses 15-minute margin between actual and scheduled departure time for a flight to be considered "on-time"

15 minutes

what is the margin between actual and scheduled departure time for a flight to be considered “on-time'“

• Sample computation...

  e.g. Airline XYZ operates only one aircraft, with 10 flights assigned to it yesterday. There were 3 delayed flights (one flight incurred 10 minutes in the morning, another incurred 18 minutes in the afternoon and the last flight was 130 minutes delayed.)

  Yesterday's Dispatch Reliability = 80%

Technical Dispatch Reliability

Reliability Engineering Deals only with what in Dispatch Reliability

Technical Dispatch Reliablity

exclude delays/cancellation that were not related to, nor caused by aircraft technical or maintenance situations. (e.g. late arrival of crew member, late catering supplies, etc.)

• Sample computation... previous case re-analyzed.

  e.g. Airline XYZ's first delayed flight in the morning was caused by the flight crew arriving late, the second in the afternoon was caused by the catering supplies' late provisioning while the last was due to its aircraft's LH MLG Wheel found with worn-out tread, thus leading to replacement that delayed the flight.

  Yesterday's (Technical) Dispatch Reliability = 90%

Dispatch Reliability

The level of analysis and technical aviation background of the Reliability Engineer would enable him to quantify and filter out only those delays that were due to engineering & maintenance-related scenarios.

Technical Dispatch Reliability

is given significant consideration and watch by th emanagement, as it directly links Operations and M&E

Technical Dispatch Reliability

as a product of Reliability Engineering, it reflects the impact of maintenance on the airline’s performance

Poor Technical Dispatch Reliability

meansan aicraft/airline(fleet) is not reliable to serve on-time, due to the maintenance of its aircraft

Component Reliability

focuses on the reliability of an aircraft component’s performance

Component Reliability

data is gathered from history of reported defects of a component or times it has been replaced due to failure, etc

Failure

termination of th eability to perform its required function as specified in an engineering specification, drawing and/or certification

Compoment Reliability

measured by quantifying howoften an aircraft component dails, via Mean Time Between Failure (MRBF) expressed in flight hours (FH)

Mean Time Between Failure (MTBF)

how is component reliability measured

Lom Mean Time Between Failure (MTBF)

indicates an un-reliable component

Component Reliability Rate Formula: resulting in XXXX MTBF

R

nuber of times that the component was removed due to failure

FH

duration of time (in flight hours) from installation to removal, of a ll similar components removed due to failure, averaged

Component Reliability

Usually also measured by the number of times a component was reported defective, removed unscheduled, through Pilot Reports (Pireps)

Component Reliability thru Pirep Rate: resulting to N.NN rate (or chance) that the component is reported faulty over the course of 1,000 flying hours

Pr

number of Pireps pertaining to the specific component

FH

time (in fligh hours) accrued by all aircraft wherein the similar specific component is installed

High Pirep Rate

may imply that the component is un-reliable

Approach

is prone to subjectivity - which could not ensure to determine failures’ root causes

Pirep

is a useful tool for detecting poor maintenance/malpractices, coupled with a good quality system

Systems Reliability

Focuses on reliability of individual aircraft systems' performance, measured by how often an aircraft system (e.g. ATA 21) fails.

Poor Systems Reliability

has a safety impact because typically it may cause unexpected transition from one operating mode to another

System Reliability Rate

becomes the reliability indicator, showing an average number of failures (or unscheduled removals’) of components in a system to a thousand hours of flight over a specified timeframe

ATA 100

system reliability is monitored according to what ATA specification

Component Failures (System Reliability)

If through ______________, same approach with MTBF of component failures but must take into account all failed components associated with the aircraft system.

Component Unscheduled Removals (System Reliability)

If through ____________, same approach with MTBUR of components taking into account all Pirep triggers and unscheduled removals c/o maintenance troubleshooting, on such components associated with the aircraft system.

System Reliability thru Pirep Rate

• Scope of analysis' timeframe must be considered... in a month? in three moving-months? In twelve months?

Pr

number of Pireps on components of a specified system

FH

time (in flight hurs) accrued by a fleet type having the specified system

Powerplant reliability

Consider its reliability as a component, an expensive aircraft part with due attention - while at the same time monitored as system, with ATA 70+ codes being dedicated to the Powerplant's several systems (Fuel, Indicating, Control, Ignition, etc.) containing numerous components.

Powerplant Reliability

Component Reliability and System Reliability approach are applied

1. Aircraft Design Phase - Initial Airworthiness

2. Aircraft Operation - Continuing Airworthiness

2 Art and Science Behind Aircraft Reliability Engineering

Aircraft Design Phase - Initial Airworthiness

• no perfect design, most especially for first-time inventions and aircraft/aeronautical products

• design mindset of installing only components (or adopting system configurations) with proven desireable reliability

• If designing a totally new aircraft however, components and systems are prototyped.

• The prototypes undergo numerous tests supported by Reliability Prediction tools such as Empirical Methods of MIL-STD-1629 (Parts Count and Stress), FMEA (Failure Mode and Effects Analysis) and FTA (Failure Tree Analysis).

• Maintenance Program (through Maintenance Planning Doc -MPD) developed as part of ICA (Instructions for Continued Airworthiness, required by the applicant's State of Design Authority for the approval of a type design.)

• Reliability Engineering processes and principles are involved during design and development of the MPD.

Aircraft Operation - Continuing Airworthiness

• Airline operators (AOC) develop their own Maintenance Programs basing on the MPD and all other ICAs provided by the Design Approval Holder / TC Holder.

• The Aircraft Maintenance Program (AMP) then requires approval from the relevant Aviation Authority.

• AMP establishes the maintenance tasks and intervals for the operated aircraft, in order to maintain its airworthiness.

• Through the Reliability Program, the Aircraft Maintenance Program is reviewed, analyzed and improved.

Airline Operators (AOC)

develop their own Maintenance Programs basing on the MPD and all other ICAs provided by the Design Approval Holder/TC Holder

Aircraft Maintenance Program (AMP)

requires approvalfrom the relevant Aviation Authority

Aircraft Maintenance Program (AMP)

establishes the maintenance tasks and intervals for the operated aircraft, in order to maintain its airworthiness

Reliability Program

through the ___________. the Aircraft Maintenance Program is reviewed, analyzed and improved

Hard Time (HT)

• item must be removed from service at or before a specified time

• Regardless of the component’s condition

• Examples:

  • Engine Life Limited Parts

  • Landing Gear Components

On-Condition (OC)

• Repetitive Inspections or tests

• To determine the condition of units, sytems, or portions of structure

• Thus ensuring continued serviceability

• The condition will determine the subsequent corrective actions

• Examples

  • Engines

    • Borescope inspection

    • Oil Analysis

    • Health Monitoring

  • Brake Wear Pins

Condition Monitoring (CM)

• Not a preventive maintenance process

• Allows failures to occur

• Data-driven iterative process

• Analysis of operating experience determines the appropriate action

• Data on the populations of items is analyzed

• Examples:

  • Avionic Computers

  • Hydro/Mechanical/Electrical Systems

Failure modes

_________ of condition monitored items do not impact safety

Soft Time (ST)

• used to recommend ‘opportunity maintenance”

• interval above which preventive maintenance is considered to be cost effective

• What airlines may choose to implement

The Reliability Program

1. Speific Flow of Information

2. Identified data Sources

3. Procedures for Data Transmission within #1

3 must haves of Data Collection, Sources and System

Typical Sources of Data

Data Analysis

after collecting the data for a given month, they are statistically analyzed and the data of aircraft availability and reliability is obtained

Data Analysis

the process of evaluating mechanical performance data to identify characteristics indicating a need for:

• Maintenance Program adjustment

• Revision of Maintenance Practices

• Hardware improvement (modification) ... and many more.

Data Analysis

• the parameters are to be monitored as a large whole, so that the Reliability Program would be as effective as possible.

• This may be well illustrated by an "iceberg".

Data Analysis Iceberg

it is evident that the reports and complaints (of pilot/technical staff) themselves do not indicate which problem has the largest effect on aircraft operations and that operative interruptions (technical occurrence, interrupts in flight, failures) show only the tip of the "iceberg" and not the cause of the problem.

Collected Data

is compared against a standard, representing acceptable performance

Performance Standards

acceptable performance

Performance Standards

• Can be alert type or non-alert type

• Statistical analysis with engineering level of judgment

• Reliability core areas considered and utilized in analysis (TDR, Component Reliability, System Reliability, Power-plant Reliability, etc.)

• Significant issues are identified and given attention

Alert Type Programs

• uses statistical parameters such as per 100 or 1000 departures or 1-month or 90-moving days, removals per 1000FH, etc

  • When running graphical or tabulated display of performance are compared with a standard level of performance, trends can show if still within or out-of-limits(levels).

• Analyzed through System reliability, reinforced by component removals or confirmed failure data

  • the CM process can be readily accomodated by this analysis program type

Upper Limits

are used to express performance standards

Performance Standards

representing a reliability band or range, by which analyzed data (compared) is interpreted

Alert Type Programs

• Alert levels can range from 0.00 failure rate per 1,000 FH both for important components, where failures in-service have been extremely rare; and to perhaps as many as 70 Pilot Reports per 1,000 hours on a systems basis for ATA 25, or 20 removals of PSU in a similar period.

Typically used Methods of Calculating Alert Levels

Alert Levels

must be re-calculated after getting new data, for forecast applications

Non-Alert Type Programs

• collected data to assist in the day-to-day operation of the maintenance program may be effectively used as a basis for continuous mechanical performance analysis

• Flight service difficulties (RTB, ATB, etc.), ATL review, Engine Monitoring reports, Incident reports, SFR / Component Analysis Reports are suitable data sources.

• This is similar to an "Alternative Means of Compliance" approach, whereas reliability data and analysis must be sufficient as equivalent to statistical "Alert-Type" programs.

Corrective Actions (CA)

triggered by identified trendline that exceed alert levels

Reliability Engineer

validates the exceedance and investigates for the root cause that must be addressed

Corrective Actions (CA)

• Must effectively restore performance to an acceptable level (based on performance standard) within a reasonable time.

• Must address the root cause behind failures/anomalies of a system or component based on reliability "data analysis".

Root Causes

are sometimes identified as several various kinds i.e. technical design weakness, improper operation or maintenance, poor maintenance/servicing, weak maintenance program, human factor-related, etc

1. Fishbone Diagram

2. Fault Tree Analysis

3. Failure Mode and Effect Analysis

4. Cause Mapping

5. Keepner Tregoe

6. etc

6 Methods for Root Cause Analysis

Reliability Program

must include procedures for notification to and mandating the organizational element responsible for resourcing and taking the corrective action

Reliability Engineer

1. Provides lubrication to the gears or have them replaced, re-designed, etc

2. Operates the gears to function

3. Monitors system-wide

4. Analyzes stuck-ups

5. No-stuck ups? well, improve

6. Back to #1

Alert Type Program

CAAP prescribes:

• Development of monthly report

• To contain all aircraft systems controlled by the Prog.

• Highligh Systems that exceeded established Performance Standards, discuss CA taken or planned

• Exmplain changes made or planned for the AMP

• Discuss continuing ‘over-alert’ conditions from previous reports

• Report progress of CA Programs

Non-Alert Type Program

CAAP prescribes:

• Consoiidation or summary of significant data/report being used, in controlling their Program

• Discuss continuing ‘over-alert’ conditions from previous reports

• Discuss continuing ‘over-alert’ conditions from previous reports

• Report progress of CA programs

Reliability Program Output

directly affects or will always be involved with the operation, maintenance and/or design & dev’t of Class I & II aeronautical/aerospace products