Synergy version = (worldmodel functional) 
*helicopter* (sv_cheats 1 required)
-make 3 cfg. files-

1st.cfg =  prop_dynamic_create combine_helicopter.mdl; ent_setname heli4; bind e "exec 2nd.cfg"

2nd.cfg = ent_fire heli4 setparent !activator; +duck; r_drawviewmodel 0; sv_maxspeed 1000; sv_accelerate 10; cl_forwardspeed 1000; r_screenoverlay effects/combine_binocoverlay.vmt; play npc/attack_helicopter/aheli_charge_up; wait 50; play npc/attack_helicopter/aheli_rotor_loop1; give weapon_mg1; use weapon_mg1; sv_gravity 100; +jump; wait 15; noclip; +moveup; wait 15; sv_gravity 600; -moveup; -jump; sv_noclipaccelerate 3; sv_noclipspeed 1.2; god; bind e "exec 3rd.cfg"

3rd.cfg =  ent_fire heli4 clearparent
alias +user "+use"
alias -user "-use"
bind e +user; 
sv_maxspeed 1000; god; sv_accelerate 10; cl_forwardspeed 1000; r_screenoverlay 0; play npc/attack_helicopter/aheli_damaged_alarm1; r_drawviewmodel 1; -moveup; sv_noclipaccelerate 7; sv_noclipspeed 7; noclip; wait 150; ent_remove heli4; -duck"

now type in autoexec: bind = "exec 1st.cfg"


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Half life 2 version = 
*helicopter* (sv_cheats 1 required)
-make 3 cfg. files-

1st.cfg =  prop_dynamic_create combine_helicopter.mdl; ent_setname heli4; bind e "exec 2nd.cfg; wait 200; ent_create env_entity_dissolver; ent_fire env_entity_dissolver dissolve heli4"

2nd.cfg = ent_create env_entity_dissolver; ent_fire heli4 kill; r_drawviewmodel 0; sv_maxspeed 1000; sv_accelerate 10; cl_forwardspeed 1000; r_screenoverlay effects/combine_binocoverlay.vmt; play npc/attack_helicopter/aheli_charge_up; wait 50; play npc/attack_helicopter/aheli_rotor_loop1; give weapon_ar2; use weapon_ar2; sk_max_ar2 5000; noclip; +moveup; sv_noclipaccelerate 2.5; sv_noclipspeed 1; god; bind e "exec 3rd.cfg"

3rd.cfg =  alias +user +use; alias -user -use; bind e +use; sv_maxspeed 1000; sv_accelerate 10; cl_forwardspeed 1000; r_screenoverlay 0; play npc/attack_helicopter/aheli_damaged_alarm1; r_drawviewmodel 1; lastinv; -moveup; sv_noclipaccelerate 7; god; sv_noclipspeed 7; noclip"

now type in autoexec: bind = "exec 1st.cfg"

Synergy version: -instructions- press "=" to spawn a helicopter. Walk up to the side of it, then face parallel with it and press "e" to get in and control it. When you are done, just press "e" again to get out. that's it :)

(On the server I play on, we get out on high parts...the server has sm_parachute :) )

demonstration: http://www.youtube.com/watch?v=HnZlYZ4NGcE&feature=plcp

//--------------------------------------------------------------------------------------------- Half Life 2 version: -instructions- press "=" to spawn a helicopter. Walk up to it and press "e" to get in and control it. When you are done, just press "e" again to get out. that's it :)

demonstration: http://www.youtube.com/watch?v=IDDlKQDiZag&feature=g-upl