INTRODUCTION

This chapter states the requirements for static strength and freedom from deformation which might adversely affect the airworthiness, handling or maintenance.

The requirements apply to airframes and mechanical components, including undercarriages and systems.

Critical design cases, corresponding to the most severe authorised use of the aeroplane, must be identified and the loads associated with each case must be traced through the structure.

All Grade A details must be identified and for each of them an allowable stress or strength must be determined. This would normally be the appropriate allowable ultimate stress or strength determined on a 'B' value basis. Refer to' Chapter 400, para 2.2 for definition of Grade A details.

The allowable ultimate stresses or loads must not be exceeded at the design ultimate load, normally 1.5times the maximum load in the design case (the design limit load).

The structure as a whole must be tested to the design ultimate load and supplementary evidence must be provided that 'B1 values are not exceeded. It is, of course, for the designer to decide what material allow ables should be associated with his own design procedure in order that this requirement is satisfied.

In addition, it must be shown that no detrimental deformations occur at loads of at least 75% of the design ultimate load.

It must be shown that these proof and ultimate requirements can be satisfied under the most adverse loading and environmental conditions. For composites these conditions apply with the structure at the most adverse moisture level that is expected to occur during the life.

Flight load measurements must be made at an early stage to confirm design assumptions.

In service a programme of operational loads measurement must be maintained to ensure that any new critical loading actions, are identified so that appropriate action can be taken.

All compliance procedures and judgements are subject to the approval of the Aeroplane Project Director (in conjunction with Airworthiness Division, RAE).

Definitions are given in para 7.

Advice on compliance with these requirements is given in Leaflets 20011 to 20014.