text: Since the problem is one of high speed flight, 
  is generally desirable to have ‘very high 
  it 
  natural 
  flutter speeds well 
  above the normal operating speeds. Any 
  change of stiffness or mass distribution will 
  alter the modes and frequencies and thus allow 
  a change in the flutter speeds. If the aircraft 
  is not properly maintained and excessive play 
  and flexibility exist, flutter could occur at 
  flight speeds below the limit airspeed. 
  
  frequencies and 
  
  Compres&ility pmblems may define the limit 
  airspeed for an airplane in terms of Mach num- 
  ber. The supersonic airplane may experience 
  a great decay of stability at some high Mach 
  number or encounter critical structural or 
  engine inlet temperatures due to aerodynamic 
  heating. The transonic airplane at an excessive 