Inspection Processes Related to Aircraft Engines

Process Review by Sofema Online (SOL) www.sofemaonline.com 

Introduction

Borescope inspection is a skill, which can be learnt. Inspectors are able to see through the scope easily recognizable defects (If present) and are able to interpret with minimal subjectivity. The proficiency that comes with experience allows Inspectors to identify subtle issues like the shifting of a burner can, for instance, that might otherwise go unnoticed.

For inspection purpose, the turbine engine is divided into two main sections: the cold and hot.

Maintenance of the compressor, or cold section, is one of concern because damage to blades can cause engine failure. (Damage to the blades often arises from foreign matter being drawn into the turbine engine air intakes.)

Minor damage to axial-flow engine compressor blades may be repaired if the damage can be removed without exceeding the allowable limits established by the manufacturer.

Inspection and Cleaning

Accumulation of dirt on the compressor blades reduces the aerodynamic efficiency of the blades with resultant deterioration in engine performance. The condition can be remedied by periodic inspection, cleaning, and repair of compressor components.

Minor damage to axial-flow engine compressor blades may be repaired if the damage can be removed without exceeding the allowable limits established by the manufacturer.

Aircraft Turbine Engine Combustion Section Inspection

The following are general procedures for performing a hot section (turbine and combustion section) inspection:

a) The entire external combustion case should be inspected for evidence of hotspots, exhaust leaks, and distortions before the case is opened.

b) After the combustion case has been opened, the combustion chambers can be inspected for localized overheating, cracks, or excessive wear.

c) Inspect the first stage turbine blades and nozzle guide vanes for cracks, warping, or FOD.

d) Inspect the combustion chamber outlet ducts and turbine nozzle for cracks and for evidence of FOD.

Borescope Inspection Considerations

Borescopes are typically used as part of scheduled maintenance or for trend / condition monitoring. A number of manufacturers require borescope inspection for certain parts. (For most combustion chamber and turbine blade inspection needs, borescopes are an invaluable tool.)

Concerning Engine Inspection - Borescopes are typically used to inspect the following areas:

 a) Turbine blades (corrosion, Foreign-Object Damage (FOD))

 b) Fuel nozzles (corrosion, physical damage, carbon buildup)

 c) Burner can (cracking, hot spots indicating uneven flame distribution, corrosion on housing welds)

 d) Igniter (corrosion, although this part is usually relatively easy to remove for

 e) Inspection with the naked eye)

 f) Air cooling holes (corrosion)

Types of Borescope

The two most common types of borescopes used in aircraft inspection are rigid and flexible borescopes.

Rigid Borescopes - offer the highest resolution and brightest images and are more durable as well as more economical.

Rigid borescopes are used when the area to be inspected is reachable in a straight path, as in many machined parts, tubes, and some moulded parts.

For many turbine blade and combustion chamber inspections, a rigid borescope is the best bet.

Flexible Borescopes - If the pathway to the inspection area is indirect or through a curved pipe, bent tube, or complex casting, then users should consider a flexible borescope.

Flexible Borescopes employ a fibre-optic bundle housed inside a flexible sheath. The resolution of a flexible borescope is defined by the number of optical fibres in the instrument’s imaging bundle (up to 30,000 pixels).

Further Guidance

 Sofema Aviation Services (SAS) (www.sassofia.com) and Sofema Online (SOL) www.sofemaonline.com provide training for aircraft inspectors delivered as classroom, webinar & online. For Details please email office@sassofia.com or online@sassofia.com