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Sunday, July 24, 2011

On-Condition Maintenance of Aircrafts: An overview 03 of 04

Previous: Part 01 - Part 02 - Acronyms
Time duration specified by the Dutch Civil Aviation authorities for performing monitoring & inspection as part of an On-Condition Maintenance programmes of some critical components are as follows:

Details and Remarks
1 Operate engine in flight 1 flight of 1 hour duration each month as a minimum
Engine deterioration in the form of corrosion (rust) and the drying out and hardening of composition materials such as gaskets, seals, flexible hoses and fuel pump diaphragms can occur if an engine is out of service for an extended period of time. 1 This utilisation requirement must be stated in the AMP.
Operate engine in flight 15 hours per 6 months as a minimum
Engine reliability and the possibilities for adequate engine monitoring are adversely affected when engine utilisation is lowered. Therefore, for operations beyond TC-holders recommended overhaul intervals, in the AMP the aircraft utilisation must be set with a minimum as stated on the left.
2 Oil Change 50 flight hours or 6 months, w.o.f.
Oil degrades over time and gets contaminated with particles during engine operation.
3 External Condition Inspection 50 flight hours or 6 months, w.o.f.
The engine should be examined externally for obvious defects such as a cracked crankcase, excessive play in the propeller shaft, overheating and corrosion, which would make it unacceptable for further use.
4 Examination of oil filters and magnetic plugs 50 flight hours or 6 months, w.o.f.
Such examination may be sufficient to show that serious wear or breakdown has taken place and that the engine is unacceptable for further use.
5 Oil contamination check by means of oil analysis 50 flight hours or 6 months, w.o.f.
Particle content is determined for various materials, which provides indication of specific engine wear. Requirements:
A) At least 10 flight hours are required per oil sample, to ensure representative data.
B) Analyse the trends for the various materials’ particle content to detect anomalies. Besides trending the individual material’s particle content, also trending the ratios between the contents of the various materials provides valuable information and should be included.
Note: several organisations monitor large numbers of engines and are able to compare individual results with a fleet average, enabling an even more reliable analysis.
C) Trend analysis and determination of follow-up action (which may include maintenance action to further determine the condition), must have been accomplished before the next sample is taken.
D) Refer to manufacturer data for additional criteria or guidelines.
6 Oil consumption analysis 50 flight hours or 6 months, w.o.f.
If engine wear increases oil consumption usually increases. Tasks:
A) Ensure that the maximum absolute value is not exceeded; and
B) Monitor the trend to detect anomalies.
7 Differential compression test or “dynamic” compression test 50 flight hours or 6 months, w.o.f.
A) Ensure that the minimum and maximum absolute values and ratios are not exceeded; and
B) Monitor the trend to detect anomalies to the individual cylinders, pistons and valves.
8 Power check 50 flight hours or 6 months, w.o.f.
A) Monitor the trend of maximum obtained power to detect anomalies.
B) Monitor the trend of at least one parameter that indicates carburettor dynamic performance, if the carburettor is included in the O/C programme.
C) Check the engine for smooth and constant running throughout the power check.
A graphical representation of On-Condition Maintenance programme being applied on the MiG-29 aircraft in service with the Serbian Air Force and air Defence
Some methods & technologies utilised for carrying out such inspections include,
  • Vibration Analysis
  • Acoustic Emission
  • Acoustic Emission
  • Ultrasonics
  • Infra-Red Thermography
  • X-ray Radiography
  • Trend Analysis
  • Spectrum Analysis
  • Inspection using a Fiberscope
  • Remote Visual inspection
Read subsequent portions: Part 04