Aero engine inspection.

A visual inspection is needed to determine the condition of aero engines and components. An annual or 100-hour inspection should include the engine and nacelle group as follows.

a.Cold Cylinder Check. If an engine is running rough the cause may be a bad ignition lead, a spark plug not firing, a partially clogged fuel injector, or a bad magneto. The dead cylinder will be colder than the surrounding cylinders and can be quickly determined by using the recommended cold cylinder checks. This should be done using thermocouple probes which are very sensitive to small differences in temperature, which is the case with a partially clogged injector. For a carbureted engine, the following check may be helpful:

b. Piston Engine Sudden Stoppage Inspection. Sudden stoppage is a very rapid and complete stoppage of the engine. It can be caused by engine seizure or by one or more of the propeller blades striking an object in such a way that rpm goes to zero in less than one complete revolution of the propeller. Sudden stoppage can cause internal damage to constant-speed propellers; reduction drive; gear train damage in the accessory section; crankshaft misalignment; or damage to accessories such as magnetos, generators, vacuum pumps, and tach generators.

Every engine that suffers a sudden stoppage must be inspected in accordance with the manufacturer's maintenance instructions before being returned to service.
Using experienced personnel, run the engine on the bad magneto for approximately 30 seconds at 1200 rpm. Without switching the magneto switch back to both shut off the engine. Have another mechanic use a grease pencil (non-carbon), and quickly mark each exhaust stack approximately 1 inch from the flange that holds the exhaust stack to the cylinder. Next, check the exhaust stacks and look for the exhaust stack whose grease pencil mark has not turned to a grayish-white or ash color. This is the cold cylinder.
The probable cause of the cold cylinder is either a defective spark plug or ignition lead. Switch spark plugs to another cylinder and run the test again. If the problem stays with the original cylinder, the problem is either the ignition lead or the magneto.
If the engine manufacturer does not provide the required information, then the engine case must be opened and every major component part must be inspected using visual and/or non destructive testing NDT procedures as applicable.
The sudden-stoppage inspections include: checking for cowling, spinner, and airframe cracks and hidden damage; and alignment of the engine mount to the airframe, the mounting hardware, isolation mounts, and checked for distortion, cracks, and elongated bolt holes. The damaged propeller must be sent to  FAA-certificated repair stations for complete aircraft NDT and repair.
Engine accessories such as: magnetos, starters, fuel pumps, turbochargers, alternators, or generators must be inspected in accordance with the manufacturer's maintenance manual on sudden stoppage or overhaul procedures to determine the product's airworthiness.

Reciprocating Engines (Direct Drive). Preliminary inspection before tear down.
(1) Remove the engine cowling and examine the engine for visible external damage and audible internal damage.
(2) Rotate the propeller shaft to determine any evidence of abnormal grinding or rubbing sounds.
(3) With the propeller removed, inspect the crankshaft flange or splines for signs of twisting, cracks, or other deformation. Remove the thrust-bearing nut and seal and thoroughly inspect the threaded area of the shaft for evidence of cracks.
(4) Rotate the shaft slowly in 90-degree increments while using a dial indicator or an equivalent instrument to check the concentricity of the shaft.
(5) Remove the oil sump drain plug and check for metal chips and foreign material.
(6) Remove the oil screens and inspect for metal particles and contamination.
(7) Visual inspection of engine case exterior for signs of oil leaks and cracks. Give particular attention to the propeller thrust
(8) Inspect cylinders and cylinder holddown area for cracks and oil leaks. Thoroughly investigate any indication of cracks, oil leaks, or other damage.

Aero engine internal inspection requirements.

(1) On engines equipped with crankshaft vibration dampers, remove and inspect the cylinders, and inspect the crankshaft dampers in accordance with the engine manufacturer's inspection and overhaul manual. When engine design permits, remove the damper pins, and examine the pins and damper liners for signs of nicks or brinelling.
(2) After removing the engine-driven accessories, remove the accessory drive case and examine the accessory and supercharger drive gear train, couplings, and drive case for evidence of damage.
(a) Check for cracks in the case in the area of accessory mount pads and gear shaft bosses.
(b) Check the gear train for signs of cracked, broken, or brinelled teeth.
(c) Check the accessory drive shaft couplings for twisted splines, misalignment, and run-out.
(d) Check connecting rods for cracks and straightness.

Reciprocating Engines (Gear-Drive). Inspect engine, propeller and components.
(1) Remove the propeller reduction gear housing and inspect for:
Loose, sheared. or spalled cap screws or bolts.
Cracks in the case.
Accessory and Drive Inspection. Check the drive shaft of each accessory, i.e., magnetos, generators, external superchargers, and pumps for evidence of damage.
(2) Disassemble the gear train and inspect the propeller shaft, reduction gears and accessory drive gears for nicks, cracks, or spalling.

Engine Mount Inspection.

(1) Examine the engine flex mounts when applicable, for looseness of engine to mount, distortion, or signs of wear.
(2) Inspect the engine-mount structure for bent, cracked, or buckled tubes.
(3) Check the adjacent airframe structure firewall for cracks, distortion, or wrinkles.
(4) Remove engine-mount bolts and mount hold-down bolts and replace.

Crankshaft inspection and repair.

Carefully inspect for misalignment and replace if bent beyond the manufacturer's permissible service limit. Worn journals may be repaired by regrinding in accordance with manufacturers' instructions. It is recommended that grinding operations be performed by appropriately-rated repair stations or the original engine manufacturer. Common errors that occur in crankshaft grinding are the removal of nitrided journal surface, improper journal radii, unsatisfactory surfaces, and grinding tool marks on the journals. If the fillets are altered, do not reduce their radii. Polish the reworked surfaces to assure removal of all tool marks. Most opposed engines have nitrided crankshafts, and engine manufacturers specify that these crankshafts must be re-nitrided after grinding.

Exhaust-driven Supercharger Turbine Inspection.

Sudden stoppage of the powerplant can cause the heat in turbine parts to heat-soak the turbine seals and bearings. This excessive heat causes carbon to develop in the seal area and varnish to form on the turbine bearings and journals.
NOTE: Rapid deceleration or momentary slowing of a propeller may occur due to contact with tall grass, water, or snow. If this occurs, the engine and propeller should be inspected in accordance with the manufacturer's instruction or service bulletins.
(1) Inspect all air ducts and connections for air leaks, warpage, or cracks.
(2) Remove compressor housing and check the turbine wheel for rubbing or binding, and coke or varnish buildup.
NOTE: Turbine turbo supercharger disk seal rubbing is not unusual and may be a normal condition. Consult the engine manufacturer's inspection procedures and table of limits.

On-Wing Borescope Inspections.

On-Wing Borescope Inspections and Aircraft Engine Compressor Blade Repair for the current passenger aircraft operators is all about minimising downtime. Airlines now actively seek specialist organisations to support on-wing engine maintenance, particularly in the field of boroscope inspection.
In-situ blade repair resulting in improved compressor efficiency reduces the necessity for costly engine removals and subsequent aircraft downtime.                              Electronic images are now used for effective aero engine health monitoring.