Abbreviations

The Flight Test Process

1.1 INTRODUCTION

Flight test is an expensive activity, which by its very nature attracts levels of risk higher than normal operations. To ensure that all trials are conducted as efficiently and safely as possible, a flight test process has been developed over the years. This process is used, with only minor variations, in nearly all test organisations throughout the world whether they be military, civilian or based at a manufacturing facility. Many of the steps in this process have evolved as the result of painful lessons and, therefore, the authors consider them vital to the overall test activity.

It is perhaps true to say that at the beginning of their careers, flight test personnel show greater interest in the test methods that they need to apply than in the overall system used to approve, authorize and regulate test flying. Consequently it was decided to make the test process the first chapter of this book to demonstrate the importance that the authors attach to this subject. It is our belief that without an understanding of the process the knowledge contained within the rest of the book cannot be applied effectively.

Brief details of the flight test process are given below. For more details the reader is referred to the AGARD flight test techniques and instrumentation series [1.1 and 1.2]. Generally the flight test process can be broken down into three major areas:

• Flight test planning.

• Conducting the test.

• Post-test actions.

1.2 FLIGHT TEST PLANNING

Thorough planning is vital for all flight trials to ensure that they are conducted safely, efficiently and that the trials objective is met. When a trial is first proposed to a test establishment a management plan is produced which includes a work breakdown structure defining the individual elements of the trial. For each element the department or departments which are to undertake the work are determined together with costs and timescales. Part of the management plan is to define the exact project technical objectives and it is at this level that this book will examine the planning process.

1.2.1 Technical objectives

To define the project technical objectives the exact requirements of the customer calling for the trial have to be understood clearly. Once this has been done then the next step is to decide on the assessment philosophy, in other words ‘What are we going to do? – How much of it are we going to do?’ Deciding on what approach to take depends on a number of factors such as the level of expertize within the test organization, the resources available, and if the trials results need to be compared with earlier results using a particular test method. The approach to the trial and the scope of the work both depend on the requirement to collect evidence and to identify where that evidence is located.

Determining what evidence is needed to be able to make well-supported recom­mendations relies upon the professional knowledge of the test team, although previous trials may provide a guide. The evidence itself does not necessarily need to come from a flight conducted as part of the trial, indeed because flight testing is such an expensive activity other sources of evidence are invariably considered first. These sources may be the aircraft manufacturer, who may have conducted the required test, earlier test results held at the test establishment, read across from other similar aircraft, another test organization, or possibly an operator who already has experience of the test article. Modelling and simulation are also used extensively. In each case the evidence and the source are considered carefully to determine to what extent it can be relied upon. If the existing evidence is determined to be reliable then it may be used without further testing or, more likely, a limited number of tests would be planned to ‘spot check’ the evidence to increase confidence in its validity.

Once the existing evidence has been established then the difference between this and the evidence required is what the flight trial must address, this defines the scope of the test. The team then decides how much testing is required to gather the missing evidence to allow the test objective to be met. From this is defined the detailed work breakdown structure including test techniques, required environmental conditions, trials location, the order and interdependency of tests, and the allocation of tasks to parts of the organization. Having defined the tests to be made, the facilities required to conduct them have to be identified: these usually include the aircraft build standard, ranges, test instrumentation and equipment, the test crew and their training standard, and data replay and analysis equipment.