SYS-RAMS
Reliability, Availability, Maintainability and Safety
Reliability, Availability, Maintainability and Safety
Kartei Details
| Karten | 115 |
|---|---|
| Sprache | English |
| Kategorie | Technik |
| Stufe | Universität |
| Erstellt / Aktualisiert | 19.02.2020 / 05.01.2023 |
| Weblink |
https://card2brain.ch/box/20200219_rams
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| Einbinden |
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What is the reliability R(t) ?
R(t) = the probability that a specific failure hasn't occured up until a specific time t.
It's derrived by subtracting F(t) from 1
\(R(t) = 1 - F(T) = \int_{t}^{\infty} f(x) dx \\R(0) = 1 \\R(\infty) = 0\)
How are Flight Hours converted into Operating Hours?
Often it is assumed that 1 Flight Hour = 1.25 Operating Hour
How is the Mean Time To Failure (MTTF) calculated?
By integrating the Reliability function R(t)
\(MTTF = \int_{0}^{\infty} R(t) dt\)
what is the difference between Mean Time To Failure (MTTF) and Mean Time Between Failure (MTBF)?
The term MTTF is used for non repairable items
The term MTBF is used for repairable items
What does the bathtub curve describe?
It illustrates what types of failure (early life, useful life and wearout life) are caused by a time-dependant lambda(failure rate)
What does early life refer to?
If the failure rate (lambda) is time-dependant and decreases with time.
What does useful life refer to?
If the failure rate (lambda) is approximately constant and doesn't change with time.
What does wearout life refer to?
If the failure rate (lambda) is time-dependant and increases with time.
Whats the difference between a qualitative and a quantitative fault tree analysis?
In a qualitative FTA minimal combinations of components failure resulting in system
failure are analysed.
in a quantitative FTA the probability or frequency of the specific system failure are determined
State some applications for a FTA:
The FTAmay be used to:
- Quantify probability of occurrence
- Evaluate proposed system architecture:
- Hardware reliability budgets
- Development Assurance Levels (A/B/C/D)
- etc.
- Assess the impact of a design modification
- Identify the need for a design modification
- Identify unique situations that require special attention
- Show compliance with qualitative and/or quantitative safety objectives
- Provide a visual aid to qualitatively illustrate the significance of the software with respect to the failure condition classification of a top level event.
- Establish crew and maintenance tasks and intervals
The FTA is a top-down system evaluation:
The FTA is usually performed once for the design and development of an aircraft:
The FTA has to be updated constantly to assure it's correctness. After the initial FTA is performed there are THREE main FTA iterations. After the requirements have been frozen a PDR (preliminary design review) is conducted. Later, when the design is frozen a CDR (critical design review) is conducted. And finally there is a final FTA for certification purposes.
What is the at risk time?
The period of time during which an item must fail in order to cause the failure effect in question. This is usually associated with the final fault in a fault sequence leading to a specific failure condition.
What is the exposure time?
Time period between
Time when the item was last known to be operating properly
Time when it will be known to be operating properly again
What are minimal cut sets?
A Minimal Cut Set is the smallest combination of basic events causing the top event:
- All the basic events need to occur to cause the top event
- A MCS is a combination of basic events
- The complete set of MCS provides the complete set of causes of the top event
FHA
Functional Hazard Assessment
A/C
Aircraft
Reliability, Availability, Maintainability and Safety
Maintenance Significant Item
Maintenance Review Board
System Safety Assessment
Flight Hour
AFHA
Aircraft Functional Hazard Assessment
Proposed Master Minimum Equipment List
International Civil Aviation Organization
AMJ
Advisory Material Joint
System Functional Hazard Assessment
Federal Aviation Administration
ARP
Aerospace Recommended Practice (SAE)
Failure Modes Distribution
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