text: of ground effect are shown in the cases of multi- 
  engine airplanes with some engines inoperative. 
  When the power loss is quite severe, the air- 
  plane may not be capable of sustaining altitude 
  and will descend. As ground effect is en- 
  countered, the reduced power required may 
  allow the airplane to sustain flight at extremely 
  low altitude with 
  the remaining powerplants 
  In ground effect, the recipro- 
  functioning. 
  encounter a 
  cating powered airplane will 
  greater (L/D),, which occurs at a lower air- 
  speed and power required and the increase in 
  range may be quite important during emer- 
  gency conditions. 
  
  The magnitude of the interference effect due 
  to lateral separation of the wing tips depends 
  on the proximity of the wi.ig tips and the ex- 
  tent of induced Pov;. This implies that the 
  interference v-r 1 
  e grealest when the tips 
  are very close AL-L the airplanes are operating 
  at high lift coefficients. An interesting ramifi- 
  cation of this effect is that several airplanes in 
  line abreast with the wing tips quite close will 
  experience a reduction in induced drag. 
  
  An indirect form of interference can be en- 
  countered from the vortex system created by a 
  preceding airplane along the intended flight 
  path. The vortex sheet rolls up a considerable 
  distance behind an airplane and creates consid- 
  erable turbulence for any closely following air- 
  plane. This wake can prove troublesome if air- 
  planes taking off and landing are not provided 
  adequate separation. The rolled-up vortex 
  sheet will be strongest when the preceding air- 
  planes is large, high gross weight, and operat- 
  ing at high lift coefhcients. At times this tur- 
  bulence may be falsely attributed to propwash 
  or jetwash. 