Considerations Related to MSG-3 Aircraft Inspection Standards

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The Operator is responsible for the Aircraft Maintenance Program and to ensure that the relevant standards are applied.

The Inspections performed by the Part 145 Organisation must ensure adherence to the established standards as identified by the Operators AMP.

Inspection Criteria and Standards include the following:

i) Instructions for Continued Airworthiness from equipment manufacturers (OEM’s)

ii) Specific Standards identified by the Continued Airworthiness Management Organisations (CAMO)

iii) The periods at which components should be checked, cleaned, lubricated, replenished, adjusted and tested.

iv) Details of ageing aircraft system requirements together with any specified sampling programmes.

v) Details of specific structural maintenance programmes issued by the type certificate holder including but not limited to:

a) Maintenance of structural Integrity by damage Tolerance and Supplemental Structural Inspection Programmes (SSID).

b) Structural maintenance programmes resulting from the SB review performed by the TC holder.

c) Corrosion prevention and control.

vi) Repair Assessment.

vii) Widespread Fatigue Damage.

viii) Details of Critical Design Configuration Control Limitations together with appropriate procedures.

iix) Statement of the limit of validity in terms of total flight cycles/calendar date/flight hours for the structural programme

ix) Certification Maintenance Requirements (CMR’s) and ADs.

Task interval parameters expressed in the MRBR may be converted to an individual air carrier’s desired units, provided this conversion does not result in the air carrier exceeding the initial requirements of the MRBR.

The use of non-destructive inspection (NDI) methods, such as “X-ray,” “ultrasonic,” “eddy current,’ ’ and ‘ ‘radioisotope,’ ’ which are approved by the manufacturer, may be employed where appropriate.

All Maintenance Significant Items (MSI’s) identified by the manufacturer are subjected to the MSG.3 analysis.

Structural program rules (Structural inspection programs (SIP) are developed by the aircraft manufacturer to meet the inspection requirements for damage tolerance.

The types of damage considered during program development are environmental deterioration (ED) (corrosion, stress corrosion), accidental, and fatigue. Some forms of ED are age-related; therefore, inspections for this type of deterioration are controlled by calendar intervals.

These calendar inspections, plus the requirements for detecting other types of ED, and accidental (AD) and fatigue damage (FD), are contained in the SIP.

Inspection requirements include:

i) External and internal inspections

ii)  Structural sampling

iii) Age exploration programs

iv) Corrosion prevention and control programs

v) Additional supplemental structural inspections

The Zonal Inspection Program (ZIP) provides consolidation of a number of general visual inspection (GVI) tasks for each zone.

The zonal inspection may include GVI tasks derived from Maintenance Significant Items (MSI) and Structural Significant Inspections (SSI) “The ZIP contains a series of GVI tasks.

Detailed and special detailed inspections (DI) are not to be contained in the ZIP.

Zonal inspection requirements apply only to zones.

Note: Access to zones should be easily accomplished and should not require the use of special tools.

Normally, the inspection aids to be used are a flashlight and/or inspection mirror.

The entire visible contents of the zone must be inspected for:

i) obvious damage,

ii) security of installation,

iii) general condition including corrosion and leaks.

Note: There is a significant degree of subjective interpretation consider the following “obvious damage” (what is obvious to a very experienced inspector may not be apparent to a new inspector).

“Security of Installation” pre-supposes a degree of knowledge concerning the standard layout – consider the role of CS25 and the requirement for “separation” see the following example and the findings:

The 777-200 aircraft were found to differ from Boeing’s current design. In particular, the wiring to the first officer’s oxygen mask light plate differed in the follow aspects: a wire clamp was missing, the wiring was not sleeved, and a large loop of unsupported wire was found. All of EgyptAir’s 777-200 had a similar wiring configuration at the first officer’s oxygen mask location. The captain’s side wiring was similar, except that sleeving was present on all airplanes inspected. ... On one of the 777-200 aircraft, the outer layer of wiring insulation was found damaged, although the inner layer was intact and the conductor was not exposed.

Further Guidance

Sofema Aviation Services (SAS) ( and Sofema Online (SOL) provide training for aircraft inspectors delivered as classroom, webinar & online. For details please email: or

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