On-Wing Engine Preservation Procedures for CFM56-7B Engines on Boeing 737 Aircraft

Introduction to the CFM56-7B Engine

The CFM56-7B is a high-bypass turbofan engine produced by CFM International, a 50/50 joint venture between GE Aviation and Safran Aircraft Engines. This engine model powers many variants of Boeing's popular 737 family of airliners, including the 737-600, 737-700, 737-800, and 737-900.

The CFM56-7B entered commercial service in 1997 and over 8,000 units have been delivered since then, making it one of the most successful and widely used jet engine models in the world. It offers 18,500 to 27,300 pounds of thrust, giving it the capability to power single-aisle aircraft like the 737 on routes up to 3,000 nautical miles.

Some key features of the CFM56-7B include:

• High bypass ratio of 5.1:1 for improved fuel efficiency
• Single-stage high-pressure turbine
• Talon II type combustor for lower emissions
• Modular design for easier maintenance
• Dual-channel Full Authority Digital Engine Control (FADEC) system

Like all jet engines, routine maintenance is critical for the CFM56-7B to ensure optimal performance and reliability throughout its service life. One of the maintenance procedures that mechanics perform is on-wing engine preservation when an aircraft is going to be inactive for an extended period.

Purpose of On-Wing Engine Preservation

On-wing engine preservation is done when an airline plans to have an aircraft out of service and grounded for one month or longer. Parking an airplane for an extended downtime while the engines remain installed (on-wing) allows moisture and contaminants to build up inside the engine, potentially leading to corrosion and degradation.

On-wing engine preservation involves thoroughly cleaning, inspecting, lubricating and sealing the engine to prevent internal damage during the inactive period. All fuel is drained and the engine is run to completely dry out residual fuel. Oil reservoirs are refilled with fresh preservative oil intended for long-term storage. Inlet covers and plugs are installed to seal off openings. Desiccant bags are added to absorb moisture.

Performing proper on-wing preservation ensures the CFM56-7B engine remains in near flight-ready condition while the aircraft is parked. This minimizes maintenance work required to return the engine back to service when the airplane is reactivated. The engine can be quickly unsealed, inspected, serviced with regular oil, and test run to verify it is functioning properly.

CFM56-7B On-Wing Preservation Procedure

The specific steps involved in on-wing preservation of a CFM56-7B engine generally include:

1. Park the aircraft in a suitable long-term storage location, either outdoors or in a hangar.
2. Connect ground power and air conditioning carts to energize the aircraft systems.
3. Inspect the engine and verify no leaks, damage or abnormalities.
4. Review maintenance logs to ensure engine is due for no near-term overhaul or repairs.
5. Run the engine at idle power and drain all fuel from the lines until dry.
6. Perform a borescope inspection of the engine internals looking for debris, corrosion or defects.
7. Change the oil and install preservative oil intended for storage (e.g. Exxon Mobil Jet Oil II).
8. Seal off openings by installing inlet covers, tailpipe plugs, and humidity indicator plugs.
9. Insert desiccant bags into intake openings to absorb moisture.
10. Attach warning tags indicating engine preservation status.
11. Apply protective exterior coatings as needed.
12. Disconnect power carts and seal aircraft access points.

More intensive preservation procedures may be required for longer downtimes exceeding one year. The engine manufacturer CFM International provides detailed technical guidance on properly preserving CFM56-7B engines for both short and long durations.

CFM56-7B Engine Preservation on Boeing 737s

The CFM56-7B is solely used on the Boeing 737 family, with earlier -600/-700/-800 variants powered by the -7B18/20/22 models and later -800/-900 aircraft using the upgraded -7B24/26/27 engines.

When a 737 needs to be removed from service for one month or more, mechanics will follow the CFM56 preservation guidelines specifically tailored to the -7B model installed. This provides maximum protection from moisture or contamination damage while the engine stays mounted during downtime.

For example, a 737-800 being sent for long-term storage would undergo on-wing preservation on both of its CFM56-7B26 engines. This includes engine dry runs, oil changes, desiccant bags, inlet covers, and humidity plugs per the recommended procedure.

Upon reactivation from storage, mechanics would remove the preservation items, service both engines, perform test runs, and return the 737-800 to flight status. Following proper preservation procedures minimizes maintenance delays and avoids unnecessary engine repairs.

Engine Preservation Stands

While on-wing preservation protects installed engines during aircraft downtime, there are also stands designed specifically for storing spare engines in a controlled environment.

These engine preservation stands securely mount the engine horizontally and connect to interfaces for turning, instrumentation readouts, and dry motoring. They allow the engine to be periodically rotated and monitored while in long-term storage.

Key features include:

• Steel mount frame engineered for the engine model
• Integrated drive shaft and gearbox for rotation
• Oil and fuel supply lines for preservation servicing
• Electrical harnesses for engine instrumentation
• Covers and sealing plugs to protect inlets and openings

Stands are often customized for a specific engine type like the CFM56-7B. They ensure spare engines remain in ready-to-install condition even after years in storage. Stands also simplify the preservation process compared to working directly on mounted aircraft engines.

Conclusions

On-wing engine preservation is a vital maintenance procedure for safe long-term aircraft storage. For the widely operated CFM56-7B engine on Boeing 737s, proper preservation steps prevent moisture and contamination that lead to costly engine repairs down the line.

Following the engine manufacturer's technical guidelines tailored to the specific -7B model ensures optimal protection while remaining mounted during downtime. When paired with periodic preservation on storage stands, spare CFM56-7B engines can be maintained in near flight-ready condition for years when needed.

FAQs

Why is on-wing engine preservation needed?

On-wing engine preservation is performed when aircraft will be grounded for extended periods of one month or longer. It protects engines from moisture and contamination damage while remaining installed on inactive planes.

How often should preservation be done on a stored engine?

Engines should be periodically preserved according to manufacturer guidelines, usually every 1-2 months. This involves rotating the engines and checking for any issues.

What is the benefit of using preservation stands?

Stands allow easier preservation servicing of spare engines compared to working on mounted aircraft engines. Stands also provide secured horizontal mounting and enable engine rotation.

Can CFM56-7B engines stay preserved for multiple years?

Yes, with proper ongoing preservation maintenance, CFM56-7B engines can remain in storage for multiple years and still be airworthy for installation when needed.

What happens after long-term engine preservation?

After extended storage, engines go through return to service testing. This involves removal of seals/plugs, oil service, test runs, and verification that the engine operates properly before reused.