How to Conduct a Borescope on a PT6A-135A Engine

Borescope Inspection Preparation and Tools
📌 The procedure detailed is a borescope inspection of a PT6A-135 Alpha engine, which must only be performed by a licensed and trained professional.
🛠️ Reference material includes Chapter 72 of the PT6 Maintenance Manual, which contains the borescope inspection guide.
🔦 The GE XL View videops/borescope was used due to its high-quality articulation and probe diameter, allowing insertion through the inlet screen without removal.
⚙️ Specific tools required include Pratt & Whitney approved insertion tools (categorized by size: -200, -400, or -600), needed to achieve the correct angle into the hot section.

Fuel Nozzle Inspection and Removal
🔍 Fuel nozzle removal involves safety wire removal, moving transfer tubes, and using a $\frac{1}{4}$-inch 12-point socket to loosen the nozzle shroud.
🔩 Reinstalling bolts before persuasion (tapping) is prudent to ensure force is applied against the bolts rather than the fuel nozzle sheath.
💧 Fuel nozzles contain tiny fuel filters that must be cleaned regularly; inspect primary and secondary nozzles based on service bulletin requirements.

Hot Section (Combustion Chamber) Inspection
🔥 The hot section, the engine's "money maker," requires careful inspection for cracks, sulfidation, and unburnt/erosion on the combustion liner, especially around the small exit duct.
🧭 Navigating the internal structure requires practice; the probe can be twisted by fingers to get a good view of the combustion liner.
⚙️ The CT (Compressor Turbine) blades are the most critical area to inspect for cracking, as this prevents catastrophic engine failure.

Compressor Section Inspection
🌬️ The thin GE probe diameter allows inspection of the first-stage compressor by sliding directly through the inlet screen, saving significant time.
🛑 Primary focus in the compressor is looking for Foreign Object Damage (FOD) along the Leading Edge (LE) of the blades and checking for oil streaks indicating seal leaks.
🔄 The compressor can be rotated using the start generator tool (approved method) or by briefly using a tool in the Tachometer (TAC) generator drive slot (non-approved method).

Power Section (Exhaust) Inspection
💨 Inspection of the PT (Power Turbine) stator and PT blades is conducted by entering through the exhaust duct's left port.
⚠️ Although cracking is rare on the PT blades, inspect for unusual gaps on the outside, which can indicate issues like prop strikes.
🌡️ The thermocouple assembly, located around the PT stator, is where temperature indications originate, helping prevent overheating.

Key Points & Insights
➡️ Only perform borescope inspections with manufacturer-approved data and certified mechanics; do not attempt this procedure at home.
➡️ The articulation and diameter of the borescope probe are crucial features for efficient inspection, especially accessing areas without removing components like the inlet screen.
➡️ The CT blades in the hot section represent the most critical area due to the risk of sulfidation and cracking, requiring thorough 360° verification.
➡️ Be extremely cautious not to spin the prop shaft or allow it to windmill while the borescope is inserted through the PT stator area.

📸 Video summarized with SummaryTube.com on Mar 03, 2026, 08:37 UTC