Inspecting a CFM56 jet engine – Opening an Engine Cowl

 

CFM56 Jet Engine - aircraft engine maintenance

CFM56 Jet Engine - Credit: Wikipedia - David Monniaux

Imagine working on an Airbus A320, doing routine aircraft engine maintenance of a GE/SNECMA CFM56 jet engine. CFM is a combination of two major aircraft engine manufacturers: the French firm Snecma (SAFRAN Group) , and the U.S. firm, GE. This CFM56 jet engine is typically employed  in many current Airbus and Boeing aircraft, commonly used in many commercial flights. One of the primary factors behind the CFM56′s broad-based market acceptance has been its simple, robust design, giving it high reliability, durability and easy maintenance. In the video shown below, the exact sequence of tasks performed by an aircraft mechanic are explicitly shown by the manufacturer.  The takeaway from this video are the following points:

  • The absolute requirement for performing tasks sequentially, per the maintenance manual, is obvious
  • The need for a modest amount of physical exertion is demonstrated
  • A lot of detail work is involved in getting access to the engine accessory compartment
  • Provided each step is done correctly, this is not such a daunting task!

 

How does a CFM56 jet engine work? Here is an excellent video from SNECMA, providing some fundamental principles.

The CFM56 fan features  fan blades which are “dovetailed“, thus allowing these blades to be replaced without having to remove the entire engine, and GE/SNECMA claimed that the CFM56 was the first engine to have this capability. This dovetailed attachment method is useful for circumstances where only a few fan blades need to be replaced or repaired, such as when a bird strike damages a few blades.

Aircraft Engine Maintenance to detect fan blade failure

Several accidents have occurred with the CFM56-3C engine as a result of the failure of its fan blades. This mode of failure led to the Kegworth air disaster in Great Britain  in 1989, which resulted  in the deaths of 47 people and injuries to 74 . When the fan blade initially failed, the pilots, in mistake, shut down the wrong engine, which caused the damaged engine to fail completely, as it was powered up after losing altitude. After this Kegworth accident, CFM56 engines fitted to a Dan-Air 737-400 and a British Midland 737-400 also suffered similar types of  fan blade failures, although neither incident led to a crash or any injuries. After the second incident, the entire 737-400 fleet was grounded.

At that time, it was not required to flight test new variants of existing engines, and certification testing failed to reveal vibration modes that the fan experienced during the regularly performed power climbs at high altitude. Analysis revealed that the fan was being subjected to worse than expected high cycle fatigue stresses, causing the blade to fracture; and more severe conditions than tested for certification. After less than a month after grounding, the aircraft  fleet was permitted to resume operations once the fan blades and fan disc were replaced with better designed blades, and the electronic engine controls were modified to reduce maximum engine thrust to 22,000 lbf. , since the fatigue problems were induced above this threshold. In conclusion, the Kegworth air disaster and fan blade malfunction could have been avoided at the time by more rigorous engine testing to more realistically simulate actual aircraft operating conditions. Aircraft engine maintenance is an important way of detecting fan blade problems, and powerplant inspection is certainly an important element of an aircraft mechanic job.

by Steve Adams

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2 Responses to “Inspecting a CFM56 jet engine – Opening an Engine Cowl”

  1. Margarett Says:

    Where is the facebook like link ?

  2. admin Says:

    Hello,

    Excellent idea. I’ll look into adding this as well as my other social bookmarks. Thanks for the suggestion…