This document defines availability as the probability that a system or component is operational at a given time without failure. It discusses the relationship between availability, reliability, and maintainability. Availability is classified as inherent, achieved, or operational availability depending on what types of downtime are considered. The document also provides a component availability flow chart and equations for calculating total availability in parallel, series, and mixed systems. It lists several techniques for improving availability such as proper training, maintenance scheduling, quality lubricants, automation, and uninterrupted power supplies.

1. PRESENTED BY:
SAMEER VISHWAKARMA
M.Tech.( Production )

2. Contents
 Definition
 Relationship with Maintainability and Reliability
 Classification
 Availability and Number of Nine
 Component Availability Flow Chart
 Calculationa of Total Availability
 Improving Techniques
 References

3. Consider a Situation-
1. Today, you are in an industry
2. The shift is of 8 hours(10:00 am to 6:00 pm)
3. It has so many machines
4. Consider one machine –A Lathe Machine
5. The machine should work for 8 continuous hours
6. Suppose a component fails at 12:00 noon and it stops working
7. It took 30 minutes in maintenance of that machine
8. Again it stopped working for 30 minutes at 3:30pm.
How long the Lathe Machine did actually work in a given shift?

4. Is that 7 hours?
 Exactly 7 hours is the actual time when machine worked without
any kind of failure.
 The machine worked for 7 hours with zero failure
 Failure and maintenance time 1 hour
 Total Time = 7+1=8 hours
What will you call the ratio 7/8?
It is Availability.

5. Definition of Availability
 From Situation given, during 8 hours of shift, 1 hour is considered for any
kind of failure and its maintenance, the Availability of that machine will be 7/8
or 0.875 or 87.5% for that particular shift on specified date.
 Availability is the probability that the system/component is
operational at a given time, without any kind of failure.
 Availability could also be understood with ‘Readiness’.
 Availability does not show how many times the maintenance
was performed.

6. Relationship between Reliability, Availability and
Maintainability
Its good if you are thinking of your Smartphone smartly.

7. Classification of Availability
Availability can be classified as followings-
1. Inherent Availability
2. Achieved Availability
3. Operational Availability

8. Inherent Availability
 The steady state availability when considering only the corrective
downtime of the system.
 For a single component, this can be computed by:
- For a system, the Mean Time Between Failures, or MTBF, is used to
compute inherent availability:

9. 9
Achieved Availability
 Achieved Availability is similar to Inherent Availability except Preventive
Maintenance (PM) is also included.
 The steady state availability when considering the corrective and preventive
downtime of the system computed by looking at the Mean Time Between
Maintenance actions, MTBM and the Mean Maintenance Downtime:

10. 10
Operational Availability
 Operational Availability is the percentage of calendar time to which one can
expect a system to work properly when it is required.
 Expression of User Need rather than just Design Need.
 Operational Availability is the ratio of the system Uptime and Total time.
Mathematically, it is:
DowntimeUptime
Uptime
Ao


• Includes all experienced sources of downtime, such as administrative downtime and
logistic downtime to restore the system.
• It is also called Operational Readiness.

11. 11
Basic System of Availability
 Inherent Availability and Achieved Availability are controlled by the system
designer/manufacturer.
 Operational Availability is not solely controlled by the manufacturer due to
variations in location, resources and logistics factors under the province of
the end user of the product.

12. Availability and Number of 9
 Availability is typically described in nines notation.
 For Example- Availability of a system is considered over one year.

13. Factors Affecting Total Availability
 Hardware
 Hardware failures like File System Full error, Kernel In-Memory Table Full error, disk
full, power spike, power failure, and LAN infrastructure problem.
 Software
 Complexity of software, Size of software, Experience of team developer, Percentage
of the code which is used before in a stable project, How much test/debug is done
before releasing the product.
 Environment
 These fault can be occur by power outages, fires, earthquakes, tornadoes and other
events.
 The point is that these events cannot be predicted and when encountering with
them, the whole system becomes down for some hours or even months depending
on the damages they impose.
 Human Errors

14. Component Availability Flow Chart

15. Calculation of Availability
 Total availability calculations
are same as calculation of
Reliability.
 There are three systems-
 Parallel
 Series
 Mixed
Parallel System
Total Availability = 1-[(1-A1)(1-A2)]
=1 − [(1− 0.005)(1-0.005)]
= 0.999975
Series System
Total Availability = A1xA2
=0.995x0.995
=0.990025

16. Improving Techniques
 Proper training of plant employees
 Consistent cleaning of machines and equipments
 Proper maintenance scheduling
 Good quality lubricants
 The 5S
 Safety measures
 Automation
 Monitoring availability
 Uninterrupted Power Supplies (UPS)
 Standby Systems
 Logistics

17. References
 Elsayed, E., Reliability Engineering, Addison Wesley, Reading, MA, 1996.
 Hoda Rohani, Azad Kamali Roosta, Information Services Organization
KLM-Air France, Amsterdam
 Wendai Wang et al.,2002, IEEE, USA

18. THANK YOU!