Within the past few years, there has been a growing interest in the utilisation of airships for a variety of missions. Studies funded by NASA and the US Navy have shown that modern airships not only could perform certain tasks more economically and silently than other aeronautical vehicles (short-haul passenger and freight transport, and long-duration ocean patrol), but that they could perform unique missions, such as the V/STOL transportation of bulky loads an order of magnitude beyond helicopter capability.

The types of modern airships envisioned fall into two categories: modernised blimps and heavy-load carriers. Blimps are receiving reconsideration for their traditional role of patrol and surveillance because of their fuel efficiency and the development of modern sensing devices which require a quiet, stationary vehicle for deployment.

The topic of testability in equipment appears to generate as many different views as people asked to express an opinion. Certainly, a manufacturer's perceptive of testability appears to vary from the equipment user view. Both will agree that testability is an essential characteristic of equipment but its need is driven by different requirements. This paper presents a view of testability as seen by the users of complex military equipment in the three services. The general thesis is that the testability needs of the Royal Navy, Army and Royal Air Force must receive greater attention than at present given and that each element of the Armed Forces is faced with maintaining equipment for 20 years or more whereas industry has a much shorter period of interest.

In developing this thesis the paper starts by discussing the military requirements for testability and outlining the maintenance philosophies adopted by the three services. Procedures for establishing an effective testability programme, as part of the overall design effort, are then considered and a possible technique for the numerical assessment of testability is mentioned. Finally the paper emphasises the importance the three Services attach to the transportability of test software.

As a preview to the main discussion, the role of the Twin Gyro Unit as a component part of the weapon's guidance system is first described. The reader will appreciate that there are as many types and configurations of gyro units as there are weapons and a full treatment of the subject would be beyond the scope of this paper. For the purposes of the discussion that follows, the gyro unit chosen is the two degree of freedom, electrically driven, Rotoraced displacement gyro, as used on the Sea Eagle, Anti Ship sea skimming missile.

Complex electronic systems are structured into functional units, printed circuit boards and components. During the manufacturing process testing starts at the component level and is carried out progressively at PCB, functional test and finally total system level.

When the equipment is in service, the reverse process is followed. That is, at the system level the suspect unit is diagnosed and replaced. This unit is then tested and if faulty diagnosed to the faulty board. This in turn is tested to find the faulty component. The testing of functional units, boards and complex components (referred to here as the ‘box’) is carried out on Automatic Test Equipment both at the factory and field level. In each case the test problem needs to be addressed during design to ensure that adequate access is given to the internal function of the item.

Reliability testing for GW systems can be considered as comprising five categories of test:

1. 1. Development testing, including environmental testing, to ensure that the design is capable of performing to the technical requirements.

2. 2. Reliability demonstration testing, to provide assurance that the reliability requirements will be, or are being, met.

3. 3. Production Testing.

4. 4. Acceptance testing, to provide assurance that production missiles are achieving the required reliability.

5. 5. In-service testing, to ensure that reliability is maintained during Service conditions.

This paper surveys the particular problems experienced when applying these categories of reliability testing to guided weapons. The paper considers only the equipment in the missile, and not GW sub-systems fitted to launch vehicles, since such sub-systems are basically the same as other avionic, ground or ship-based systems from the reliability test point of view.