Development of Maintenance Programs Embry-Riddle Aeronautical University Chapter 2

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Development of Maintenance Programs Development of Maintenance Programs Embry-Riddle Aeronautical University Chapter 2

Before the Wright Flyer…

Development of Maintenance Programs  Introduction  Maintenance Steering Group (MSG) Approach  Process-Oriented Maintenance  Task-Oriented Maintenance  Maintenance Program Documents  Maintenance Intervals Defined  Changing Basic Maintenance Intervals  Summary

IntroductionIntroduction  Two basic approaches to Maintenance l Process-oriented l Task-oriented l Difference between two:  is the attitude toward maintenance actions  the manner in which actions are assigned to components and systems

 Process-oriented Approach l Hard time (HT) l On-condition (OC) l Condition monitoring (CM) Introduction

 Process-oriented Approach Process-oriented Approach l HT and OC are for components or systems that have definite life limits or detectable wear out periods (Table 1.1 – A, B, C) – pg 10 l CM items are operated to failure and failure rates are tracked to aid in future prediction or failure rate prevention (Table 1.1 – D, E, F) Introduction

 Task-oriented Approach l Uses predetermined maintenance tasks to avoid in-service failures l Redundancy and reliability programs utilized Introduction

Maintenance Steering Group Approach (MSG)  Began in 1968 (747) with reps from Boeing’s design and maintenance groups, from the suppliers, airlines who desired to purchase aircraft and the FAA.  6 working groups – structures, mechanical systems, engine and auxiliary power plant (APU), electrical and avionics systems, flight controls and hydraulics, and zonal.  Used “bottom-up” review to determine which process to use HT, OC or CM.

Maintenance Steering Group Approach (MSG)  MSG-2 used: (pg. 17) l Systems and components; structures; and engines  Step 1 identify the maintenance or structure items requiring analysis  Step 2 identify the functions and failure modes associated with the item and the effect of a failure  Step 3 identify those tasks which may have potential effectiveness  Step 4 assess the applicability of those tasks and select those deemed necessary  Step 5 for structures only, evaluate initial sampling thresholds  MSG-2 no longer used

Process-Oriented Maintenance  Hard Time (HT) l is the removal of an item at a predetermined interval (hrs, cycles, calendar time)  On-condition (OC) l item will be checked at specific intervals (hrs, cycles, or calendar time)  Condition Monitoring (CM) l monitors failure rates, removal rates etc. to facilitate maintenance planning

Hard Time (HT)  Requires item be removed and either completely overhauled, partially overhauled (restored), or discarded before exceeding the specified interval l (calendar time, engine change, cycles, flight hours, specified flights – over water etc..) l Items that can have an adverse effect on safety but no maintenance check for that condition  Rubber seals, bushing etc..  Structural inspection, landing gear overhaul, and life limited engine parts, mechanical actuators, hydraulic pumps and motors, electric motors and generators  Can be OC as long as not safety related…

On-condition (OC)  Requires item be periodically inspected or tested to determine if item can continue in service – overhaul, restore or replace l On-condition limited to continued airworthiness by measurements or tests without doing a tear-down inspection l Examples – tire tread and brake linings, scheduled borescope inspections of engines, engine oil analysis l Other include – Brake wear indicator pins l Control cables (measure for diameter, tension, and broken strands) l Linkages, control rods, pulleys etc (measure for wear, end or side play, or backlash

Condition Monitoring (CM)  Involves the monitoring of the failure rates, removals, etc. of individual components or systems that do not have a definite lifetime or noticeable wear out period  CM components are operated until failure occurs – unscheduled maintenance  FAA states regarding CM: l Item has no direct, adverse effect on safety l Must not have any “hidden function” (not evident to crew) that could effect safety l Must be in condition monitoring or reliability program l Avionics and electronic components  Basic elements include – data on unscheduled removals, maintenance log entries, on-board data systems, shop findings etc. – can be used to adjust HT and OC intervals  Only monitors failure not the condition of items

Task-oriented (MSG-3)  “Top-down” approach or “consequence of failure” – safety driven  Used to identify suitable scheduled maintenance tasks to prevent failures and maintain the inherent reliability of the system  Three categories: l Airframe systems tasks l Structural item tasks l Zonal tasks

Maintenance Tasks for Airframe Systems  Lubrication  Servicing  Inspection  Functional Check  Operational Check  Visual Check  Restoration  Discard

Maintenance Tasks for Structural Items  Environmental Deterioration l Climate or environment – may be time dependent  Accidental Damage l Result of human error or impact with an object  Fatigue Damage l Crack or cracks due to loading or stress

Inspections for Deterioration of Structural Items  General Visual Inspection l Visual exam that will detect obvious conditions or discrepancies  Detailed Inspection l Use of inspection aids, (i.e. mirrors, hand lenses) may require surface cleaning and detailed access  Special Detailed Inspection l Use of Nondestructive inspection (NDI): dye penetrant, high-powered magnification, magnetic particle, eddy current

Zonal Maintenance Tasks  Ensures all systems, components, and installations within a specified zone receive adequate screening, security of installation and general condition  Look, listen, and feel test l General visual inspection l Detailed visual inspection

MSG-3MSG-3  Failure is assigned safety and economic whether it is an evident or hidden failure  Fig. 2-2, Pg. 25 – Level One analysis  Fig 2-3, Pgs. 26, 27 – Level Two analysis

Maintenance Program Documents  Maintenance Review Board Report (MRBR) l Contains the initial scheduled maintenance program for US certificated operators l Includes the systems and power plant maintenance program, the structural inspection program, and the zonal inspection program l Also includes aircraft zone diagrams, a glossary, and list of abbreviations and acronyms

Maintenance Program Documents  Maintenance Planning Document (MPD) l Contains all the maintenance task information from the MRBR report plus additional tasks by the airframe manufacturer l Sorts tasks in various ways: letter check, hrs, cycles and calendar time l Includes diagrams showing locations and numbering of access doors and panels, aircraft dimensions, planning for maintenance checks – to include man-hour requirements

The Monthly Maintenance Plan is used to identify the projected maintenance work load such as inspections, receipts/transfers, technical directive compliance, etc. The Monthly Maintenance Plan provides requirement data for aircraft maintenance, SE material, manpower and training. The Monthly Maintenance Plan is under the cognizance of the MO. Monthly Maintenance Plan

1. Projected known operational commitments, including number of flights, flight hours, and utilization goals. 2. Dates of scheduled inspections. 3. Date of receipt or transfer of aircraft. 4. Precision Measuring Equipment (PME) calibration requirements. 5. Schedule of technical training. 6. Forced removal items. 7. Technical Directive Compliance (TDC) requirements. 8. Schedule of personnel for ejection seat safety check out 9. Schedule of pre-inspection meetings. 10. Current list of QA personnel 11. Dates of scheduled SE inspections. 12. Scheduled nondestructive inspection (NDI) requirements

Maintenance Intervals Maintenance Intervals  Most intervals are standard but airlines can create own intervals as long as the integrity of the original task is maintained or receive FAA approval  Transit Check – pre-flight and turn l Visual, open/loose panels, fluid leaks  48 hour Checks – “daily” l Wheels, brakes, fluid levels, hydraulic fluid  Hourly limit Checks – (100, 200, 250 etc.) l Engines, flight control systems

Maintenance Intervals Maintenance Intervals  Operating cycle limit Checks l Tires, brakes, landing gear, airframe structures  Letter Checks – (A, B, C, and D) l Development of 777, MSG-3 eliminated checks  Changing Intervals l Hot, humid climates – more CC l Dry, desert climates – check for sand and dust l As aircraft age intervals for some items may shorten while others may lengthen

SummarySummary  Process-oriented and Task-oriented approaches l HT, OC and CM vs. scheduled, redundancy, and reliability  MSG, MSG-2, and MSG-3 l Structures, mechanical systems, engine and APU, electrical and avionics, flight controls and hydraulics, zonal l Systems and components; structures; and engines l Straightforward logic approach; “How does failure effect operation?”  Maintenance Documents – (MRBR and MPD)  Maintenance Intervals l Transit, 48 hr, hourly, cycles, Ltr Checks l Changing Intervals

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