Lecture 1 - Context + RAMS Flashcards
RAMS (abbr.)
Reliability, Availability, Maintainability, Supportability.
Functionability (def.)
The inherent ability of a system to perform a required function with specified performance requirements and attributes, when it is utilized as specified (under certain operating conditions)
Aircraft environmental flight envelope (def.)
A given range of static temperatures and altitudes (pressures) an AC is designed to operate in.
Failure (def.)
- Every system is typically functionable at the beginning of its operational life.
- Irrespective of the perfection of the system design/technology, during operation changes occur.
- Changes that result from physical processes such as corrosion, abrasion, fatigue, deformation etc.
- As a result, the system output deviates from the specification.
“Event that results in either loss of ability to perform the required function or satisfy the required performance requirements”
Failure mechanism (def.)
The physical process that leads to failure.
Failure mode (def.)
The way a system or component functionally fails, that is, extent a certain function cannot be fulfilled anymore.
SoFu (def. + expl.)
State of functioning: system is functionable or in a ready state
SoFa (def. + expl.)
State of failure: system is no longer functionable.
Factors influencing the functionability profile
- Inherent characteristics of the system (RMS)
- Utilization characteristics
Inherent characteristics of the system (RMS)
- Frequency of occurrence of failures (Reliability)
- Complexity of the restoration tasks (Maintainability)
- Ease of support of the tasks (Supportability)
Utilization characteristics
- Operational scenario
- Maintenance policy
- Logistics function
Availability (def.)
The probability that the system will be available and capable of performing its intended function at any random point in time.
Function of RMS
Availability (metric)
= time in sofu / total time in utilization
Maintainability theory (def.)
The scientific discipline studies the tasks that need to be performed to maintain the functionability of a system.
Maintainability (def.)
The inherent characteristic of an item related to its ability to be restored when the specified maintenance task is performed as required.
Maintainability (metric)
Sofa / (# failure events)
Maintenance tasks (3x + example)
- Corrective: restore the functionability of the system after the loss of the function or performance.
- Hard-time preventive: reduce the probability of failure.
- Condition based: occur due to the monitoring of a change in condition.
Objective of hard-time preventive maintenance tasks
Happens before a transition to sofa in order to reduce:
- Maintenance cost
- Prob of failure
Types of checks w/ frequencyand duration of check
Major check (D), 18000 hrs, 25-30 days Inter check (C), 4500 hrs, 9 days Service check (B), 800-3000 hrs, 1-2 days Ramp check (A), 125-500 hrs, 0.3 days
Reliability (def.)
The inherent characteristic of a system related to its ability to maintain functionability used as specified.
(M)TTF (abbr.)
(Mean) Time To Failure
MTBF (abbr.)
Meant Time Between Failures
MTBF (def.)
Measures only the time a repairable system is available and operating (so not a measure for non-repairable systems)
Supportability (def.)
The inherent characteristic of an item related to its ability to be supported by the required resources for the execution of the specified maintenance tasks.
Factors influencing supportability (3x)
Supplies required
Accessibility
Maintenance work
Factors influencing reliability (3x)
Inherent: strength and condition of raw materials, manufacturing, quality control, initial packaging/ transportation/storage.
Environmental: temp, humid, salinity, vibrations, radiation, terrain, etc.
Operational: loading, # of cycles, the intensity of use, freq of use, misuse, and storage conditions.
