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MRO Business lecturesWeek 1: Gas turbine maintenance, leasing and contract
One group, two airlines, three businesses
The Air France-KLM group, born of the merger between Air France and KLM in 2004, has been leveraging
the complementarity between the two airlines in their three-principal business:
1. Passenger transport
2. Cargo transport
3. Aircraft maintenance services
Figure 1: Air France Industry/ KLM E&M engine capabilities
Maintenance concepts
Continuous Airworthiness Maintenance Program (CAMP)
All maintenance is based on the Continuous Airworthiness Maintenance Program, this program defines
per aircraft the maintenance requirements. Example of references:
- Part M: Operator responsibilities.
- FAA FAR 43 (Maintenance)
- FAA FAR 145: Repair station
- EASA Rulemaking
The maintenance organization is described in the MOE: Maintenance Organization Exposition.
Regulations and Controlling Authorities.
The Aviation Industry is a tightly controlled environment. Main controlling bodies for KLM:
- EASA: European Aviation Safety Agency
- FAA: Federal Aviation Administration (USA)
- CAA: Civil Aviation Administration (UK)
- CAAC: Civil Aviation Administration of China
- DGAC: Direction Générale de L’Aviation Civile (France)
And national aviation controlling agencies for the several customers.
,Quality Assurance and Quality Control and auditing system
Quality control:
- Quality Assurance and Control organization provides independent supervision and monitoring
of quality control, recognitions and authorizations.
- Liaison between aviation authorities and KLM E&M.
- Audit system: E&M facilities are frequently audited by both KLM quality control organizations
as well as customers and national aviation controlling bodies, audit remarks are required to be
solved within a defined timeframe.
On condition Maintenance Concept
Consists primarily of monitoring the aircraft and engine performance at regular intervals and
determining when and which maintenance is required based on the condition of certain operating
parameters.
Maintenance Tasks are described in MRI’s: Maintenance Required Inspections performed at fixed
intervals per certain number of flight hours.
Engine inspections include:
- Borescoping the gas path, using borescope equipment to inspect the internal gas path of the
engine.
- Oil system checks
- Visual zonal inspections
- Functional checks of certain systems
Hard time maintenance concept
Hard time maintenance concept is based on predetermined “hard times” to remove components/
engines for scheduled maintenance. Regardless of actual condition. Objective of hard time concept is
to minimize any operational disruption. Disadvantage: loss of any usable operational remaining life.
Hard time maintenance concept is not in use with many operators as main concept. With certain
reliability issues used in isolated cases for a component.
Thresholds
Thresholds counters to determine a required step in maintenance, are expressed in flight hours or flight
cycles (Take-off and landing cycles) and are used with aircraft & aircraft component maintenance and
engine maintenance.
Work scope Planning Guide
Engines shop maintenance is described in document:
- Work scope Planning Guide (WPG).
- Defines maintenance thresholds for individual modules and components.
- Lists Air Worthiness Directives.
- Service Bulletins.
- Specific maintenance tasks based on operational experiences.
- Defines performance targets after maintenance.
Engine Removal Reasons
Engines are removed for a variety of reasons:
- Replacement of life limited rotating parts like shafts and disks.
- Performance deterioration:
o Thermodynamic: Loss of EGT margin (High Exhaust Gas Temperature)
o Mechanically: High Vibration levels of the rotor system(s).
- Oil leakage/ consumption.
- Damage to the gas path due to:
o Deterioration
, o Foreign Object damage (example bird strikes).
- Findings during the regular inspections.
Shop visit process & work scoping
Figure 2: Engine Overhaul process flow
Figure 3 Engine Shop visit process MRO Process Innovation
After engine removal off wing, the engine is inducted in the shop:
- Incoming inspection is performed.
- Engineer determines work scope proposal based on:
o Engine removal season.
o Additional on wing complaints.
o Incoming inspection findings.
o Maintenance Thresholds.
, o Life Limited Parts status and required LLP replacements.
o AD & SB status
- Work scope meeting organized to discuss and finalize work scope, participants:
o Customer or customer representative
o Engineer
o Mechanic(s)
o Planning officer
- Bill of work is finalized, agreed and released.
- Engine is inducted in disassembly process.
Main cost drivers in gas turbines: rotating (life limited) parts, frames, airfoils and accessories: fuel pump,
lubrication pump etc.
Hospital repairs
Hospital repairs (repair work scope):
- Limited repairs where work is performed on specific module(s) of the engine.
- Engine located in separate repair line (hospital line).
- Thresholds are not reset to zero.
- Engine hour and cycle count continue.
Typical hospital tasks: HPC Airfoil repairs by blending through the Borescope holes or by lifting the HPC
Uppercase, Repair of the Turbine Rear Frame, replacement of Fan blades and repair of the oil leakage
complaints.
Shop visit
Depending on the amount of hours/ cycles operated and the removal reason the engine is disassembled
in modules requiring maintenance. Subject modules are further disassembled in the respective assies
and subject assies further disassembled in piece parts. Maintenance of modules is defined in thresholds.
After maintenance, thresholds are reset to zero. Full overhaul for entire engine during a particular shop
visit not likely due to the various different thresholds. Hot sections like combustor and turbines require
more frequent maintenance/ repair than colder sections.
Work scope levels
Levels of work scoping:
- Overhaul: full maintenance with reset of overhaul threshold.
- Performance: general, airfoils are removed for maintenance, rotor structures are left intact
Performance threshold is reset.
- Minimum: limited amount of work to exposed areas.
Airworthiness Directives (AD)
Notification to owners and operators of a certified aircraft that a known safety deficiency with a
particular model of aircraft, engine, avionics or other system exists and must be corrected within a
certain defined timeframe or number of flight hours or flight cycles.
AD’s are the most stringent form of maintenance required actions directly related to a safety issue and
are mandatory to comply with.
Service Bulletins (SB’s)
Issued by the Original Equipment Manufacturer (OEM). Issued to address technical issues, introduce
product improvements, introduce replacements for obsolete part numbers and inform operators/
maintenance facilities about new procedures, equipment etc.
SB’s are categorized in required levels with respect to timing of introduction. Service Bulletin
implementation subject to operator/ owner approval and acceptance. Service Bulletins related to Air
Worthiness Directives always mandatory and categorized priority one.
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