Dealing adequately with technical uncertainties

Statistics, RAMS & Quality Management
Search this site:
Sitemap
RAMS 
 
Reliability, Availability, Maintainability, Safety

The term "RAMS", originally  "RAM" without "S", comes from defense industry and is still today used only in this industry, however, European railway industry has adopted the term "RAMS" in its EN 50126 standard.
RAMS means

The "S" in "RAMS" came decades after "RAM" has been established. However, the "S" makes absolutely sense because the analytical methods for demonstrating "RAM" and "S" are the same.
The following table describes RAMS in more detail.


term
Intention
Didactic Hints
Reliability
Item must operate with as little  failures as possible
There are no requirements for repair time.  However, it is important that repairs occur as rarely as possible.
Availability
Item must be in operable condition in as much time as possible
Downtime must be as low as possible. Failures are allowed, provided that repairs take only little time.
Maintainability
Item must be repair friendly
Item design must support quick failure detection and short repair times. This will in turn support high availability.
Safety
Item must enter a safe state upon failure
Product may be unreliable and may have long downtimes and poor repair procedures, provided that, if it fails, it will enter a safe state.

Since the early 1960s, many standards and handbooks have been published by the US department of defense (Mil-HDBK-xxxx and MIL-STD-xxxx).
These documents contain requirements for army material suppliers. In the meantime, almost all of these documents have been withdrawn and made publicly available.
While de jure obsolete, many of them are de facto still authoritative in military and even civil industries.

In contrast to standards and procedures of many other industries at that time, these military requirements not only addressed product quality, but also process and production quality.

The understanding that product quality is rather the result of a good design process than an end test, was traditionally limited to those industries with high safety requirements (aviation, railway, energy supply)

While the focus of RAMS is not primarily safety, it was the intention of combining similar disciplines (RAM and S) that led to the term RAMS.
Despite the differences between RAM and Safety, the analytical methods behind are the same.
According to the author's experience, the requirement levels can be described as follows:

Goal
Military Products
Civil Industrial Products
Civil End-User Products
Reliability high
medium low
Availability high high medium
Maintainability high medium low
Safety medium
high high

Analytical methods for demonstrating RAMS requirements and goals are described here.


Privacy Policy