text: permanent deformation when subjected to the 
  limit load. 
  In fact, the components must with- 
  stand this load with a positive margin. This 
  the aircraft should 
  requirement implies that 
  withstand successfully the limit load and then 
  return to the original unstressed shape when 
  if the air- 
  the load is removed. Obviously, 
  is in 
  craft is subjected to some load which 
  excess of the limit 
  load, the overstress may 
  incur an objectionable permanent deformation 
  of the primary structure and require replace- 
  ment of the damaged parts. 
  
  There are strength requirements which ate 
  common to all aircraft. 
  In general, these re- 
  quirements can be separated into three particu- 
  lar areas. These are detailed in the following 
  discussion. 
  
  Many different flight and ground load condi- 
  tions must be considered to define the most 
  the structural com- 
  critical conditions 
  ponents. 
  flight, 
  negative lift flight must be considered. Also, 
  the effect of flap and landing gear configura- 
  tion, gross weight, flight Mach,number, sym- 
  metry of loading, c.g. positions, etc., must be 
  studied to account for all possible sources of 
  critical loads. To verify the capability of the 
  structure, ground static tests are conducted 
  and flight demonstrations ate required. 