This is a very simple method of making your character fly - just go to the jump frames and in the tag "hit_j:", link back to the first jump frame. So now, he's able to jump out of the jump - he can fly.

<frame> 210 jump
   pic: 60  state: 4  wait: 1  next: 211  dvx: 0  dvy: 0  dvz: 0 
   centerx: 39  centery: 79  hit_a: 0  hit_d: 0  hit_j: 210
   [...]
<frame_end>

<frame> 211 jump
   pic: 61  state: 4  wait: 1  next: 212  dvx: 0  dvy: 0  dvz: 0
   centerx: 39  centery: 79  hit_a: 0  hit_d: 0  hit_j: 210
   sound: data\017.wav
   [...]
<frame_end>

<frame> 212 jump
   pic: 62  state: 4  wait: 1  next: 0  dvx: 0  dvy: 0  dvz: 0
   centerx: 39  centery: 79  hit_a: 0  hit_d: 0  hit_j: 210
   [...]
<frame_end>

These example-frames should be enough, but here's a study example anyway:

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Inspired by Zizibaluba