1. Embry-Riddle Aeronautical University
The Failure Process

2. Before the Wright Flyer…

3. Scheduled Maintenance Failure Summary
The Failure Process
Scheduled Maintenance
Failure
Summary

4. Mechanical Advantage Mechanical Components subject to:
Wear
Fatigue
Possible Corrosion
Wear out may take long time – referred to as “graceful degradation”
Heat is the worst enemy

5. Scheduled Maintenance
Role is to cope with the failure process
Age at which they will fail rather than how they fail and what happens after they fail
Assumption that as items age they become less reliable and fail
Led to overall failure rate of item will be reduced by age limit
Hard Time (HT)
is the removal of an item at a predetermined interval (hrs, cycles, calendar time)

6. Hard Time (HT)
Requires item be removed & either completely overhauled, partially overhauled (restored), or discarded before exceeding the specified interval
(calendar time, engine change, cycles, flight hours, specified flights – over water etc..)
Items that can have an adverse effect on safety but no maintenance check for that condition
Rubber seals, bushing etc..
Structural inspection, landing gear overhaul, & life limited engine parts, mechanical actuators, hydraulic pumps & motors, electric motors & generators
Can be OC as long as not safety related…

7. Failure Failure is an unsatisfactory condition
Any identifiable deviation from the original condition that is unsatisfactory to a particular user
Unsatisfactory depends on the consequences of the failure in a given operating context
Loss of oil on short flight or engine on multi-engine aircraft vs long flight and single engine aircraft
Failure determination varies by organization and type / model / series of aircraft (MEL)

8. Maintenance Management Techniques
Minimum Equipment List (MEL)
List of equipment that the aircraft may be inoperative but still allowed to fly as long as it does not affect the safety & operation of flight – Tailored to mission
Determined by manufacturer & sanctioned by the regulatory authority (FAA)

9. Maintenance Management Techniques
Master Minimum Equipment List (MMEL)
Lists ALL equipment for the aircraft model – list is tailored to its MEL
Concept of the MEL is to allow the deferral of maintenance without upsetting mission requirements
Maintenance must be performed within some set of guidelines (1, 3, 10, or 30 days or cycles required) depending on operational requirements of the system
Pilot may always require or defer maintenance per the MEL
Maintenance MUST abide by decision…. (his call)
“Takes a college education to break it & a high school education to fix it.”

10. Types of Failure
Potential/Functional Failure is the inability of an item to meet a specified performance standard
Includes to function at a level that has been specified as satisfactory (i.e. water heater with 2 elements)
Must have clear understanding of its functions
Brakes – anti-skid, modulated braking or total failure

11. Types of Failure
Particular Functional Failures – identified that failure is imminent – known as potential failures – so we can continue to use until we can repair or replace before total functional failure (when convenient not when the occur)

12. Functional or Potential Failures
Clear definitions of the functions of items as they relate to the equipment or operating context in which the item is to be employed
A clear definition of the conditions that constitute a functional failure in each case
A clear definition of the conditions that indicate failure is imminent.
Must be able to define not only the failure but the precise way it is recognized

13. Perception is Reality??
Mechanics see fuel leak, super sees seep, maint chief sees weep
Aircrew see most dynamic operational failures
Monitoring systems
Master caution/Warning and on board test and recording systems make failure evident before a system is needed
Evident and Hidden functions
Evident – failure is obvious as they conduct normal duties
Hidden – failure only when called upon

14. Hidden Functions
A function that is normally active but gives no indication to the crew if it fails.
The Fire detection system.
A function that is inactive, so that crew cannot know it will be available until needed.
A fire extinguishing system or emergency egress system.

15. The Consequence of Failure
The consequence of a failure determines the priority of the maintenance activity or design improvement required to prevent its occurrence.

16. Failure Consequences
Safety Consequences – involving potential loss of equipment and its occupants.
Operational Consequences – involves an indirect economic loss as well as the direct cost of repair.
Non-operational Consequences – involves only the direct cost of the repair.

17. Failure Consequences
Hidden-failure Consequences – has no direct impact BUT increase the likelihood of a multiple failure.
Critical failure is any failure that could have impact on safety.

18. Summary Role of Scheduled Maintenance Definition of failure Hard Time
Potential and Functional Failure
Hidden Function
Four categories of Failure Consequences
Critical Failure

19. Questions?