Engine Removal, Installation, and Ground Run-Up

Engine Removal, Installation, and Ground Run-Up

Replacing an aircraft engine is one of the most consequential tasks an aviation maintenance technician performs. Every disconnected line, every reinstalled fastener, and every logbook entry carries direct airworthiness responsibility. This lesson walks through the full sequence: safe removal, careful installation, a supervised run-up, and proper documentation.

Preparation and Safety Before You Touch Anything

Before any work begins, obtain and read the manufacturer's maintenance manual (MM) for the specific airframe and engine combination. Never substitute a generic procedure for the manual-specified one — engine bays vary, and the sequence of disconnections matters.

Establish a safe work environment first:

• Fire hazard control: Remove all ignition sources from the work area. Have a correctly rated fire extinguisher within arm's reach during any fuel system work and throughout the run-up.
• PPE: Wear safety glasses and, during the run-up, hearing protection rated for the noise level present. Ground personnel must stay clear of prop arc and exhaust.
• Aircraft security: Chock the wheels, set the parking brake, and verify the magneto switch or ignition is OFF and placarded before beginning any engine work.
• Fuel and electrical isolation: Turn the fuel selector to OFF and pull or collar the master switch and magneto switch before disconnecting any fuel, oil, or electrical line. Follow lockout/tagout principles to prevent inadvertent energization.

Engine Removal

Work as a team of two or three. One person performs the physical disconnection; a second person reads from the checklist and confirms each step; the third documents on the removal checklist.

General sequence for a reciprocating engine:

1. Drain or capture fuel and oil as required; have absorbent material and approved containers ready.

2. Disconnect fuel supply and return lines — cap or plug all open fittings immediately to prevent contamination.

3. Disconnect oil lines, breather tubes, and oil cooler lines.

4. Disconnect all electrical connections (magneto P-leads, starter leads, sensor wiring). Label each connector or use the MM diagram — mix-ups during reinstallation are a common error source.

5. Disconnect engine controls: throttle, mixture, carburetor heat or alternate air, and propeller control cables as applicable.

6. Remove the exhaust system or loosen slip joints enough to clear the engine.

7. Attach an approved engine hoist rated at or above the engine weight to the designated lift points specified in the MM. Never improvise a lift point.

8. Support the engine with the hoist before loosening the engine mount bolts. Remove mount bolts in the MM-specified sequence while a team member maintains hoist tension.

9. Carefully move the engine clear of the airframe, watching for any remaining connections. Place the engine on the engine stand.

10. Cap all airframe-side fittings and bundle labeled wire harnesses to protect them from damage.

Document every disconnected item on the removal checklist as you go — not from memory after the fact.

Engine Installation

Installation is the removal sequence in reverse, but with additional inspection steps:

1. Inspect the engine mount structure for cracks, corrosion, and security before positioning the new or overhauled engine.

2. Hoist the engine into position; start all mount bolts finger-tight before torquing any of them. Torque to the MM specification using a calibrated torque wrench and mark fasteners per MM guidance.

3. Reconnect all systems in the MM-specified sequence — typically controls, then electrical, then oil, then fuel.

4. Safety-wire all fasteners designated in the MM. Use the correct wire diameter and approved technique (twisted double-strand safety wire is standard on most engine fittings); wire must pull the fastener toward tightening, not loosening.

5. Check all fluid levels — engine oil to the proper range, and verify fuel is available at the correct selector position.

6. Verify full and correct control travel for throttle, mixture, and propeller controls from the cockpit to the engine through the full range of motion with no binding.

7. Check security of all attachments: tug gently on each line and harness; visually confirm all B-nuts, clamps, and connectors are fully seated.

8. Complete the manufacturer's return-to-service (RTS) installation checklist — every line, every checkbox.

An instructor must inspect and sign off the installation before any attempt to start the engine.

Ground Run-Up

The run-up is conducted in a designated engine run area away from buildings, people, and loose debris. Confirm winds are acceptable (exhaust and noise directed appropriately) and that a fire extinguisher is manned and ready.

If the MM requires a pre-oil procedure before initial start, perform it now: motor the engine with ignition OFF until oil pressure registers, then allow the engine to stop before proceeding to start.

Follow the Pilot's Operating Handbook (POH) or Aircraft Flight Manual (AFM) checklist precisely for starting. Once running, allow the engine to warm to the MM-specified minimum oil temperature before increasing power.

For a reciprocating engine static run-up, key checks include:

• Oil pressure and oil temperature within limits
• Magneto drop check: At the MM-specified RPM, switch from BOTH to each magneto individually. The drop on each magneto must be within the limits stated in the MM (typically no more than a specified RPM drop and no more than a specified difference between the two magnetos). Excessive drop or rough running indicates a magneto or ignition system problem — document and investigate.
• Carburetor heat check: apply carb heat and note the expected slight RPM drop and then recovery.
• Engine instruments within normal range at idle and at run-up power.

Note any discrepancies on the run-up record and in the logbook. Do not return the aircraft to service with unresolved discrepancies.

Maintenance Log Entry

The maintenance record entry must include: a description of the work performed, the engine make/model/serial number, the date, the total time on the airframe, a statement that the work was done in accordance with the manufacturer's MM and applicable FAA regulations, and the technician's certificate number and signature. An operational check notation — stating that the engine was run and performed within limits — is included in the same entry. Incomplete or vague logbook entries are an airworthiness compliance failure.