i would like to know why some aircraft crash on the runaway when they appear on fs2002, they literaly sink on the runaway an fs restart and do the samething, thanks

I would assume you are talking about third party addon aircraft. I know of no fs2002 default aircraft that exhibit that behavior.You could try opening the aircraft.cfg file and locate the contact points section. Try adjust the static pitch and static cg height sections plus the vertical position of the landing gear.If the aircraft is rotating before the crash, then the overall center of gravity is incorrect and is a totally different problem requiring more changes in the *.air and aircraft.cfg file.//0 Class (0=none,1=wheel,2=scrape,3=skid,4=float,5=rudder)//1 Longitudinal Position (feet)//2 Lateral Position (feet)//3 Vertical Position (feet)//4 Impact Damage Threshold (Feet Per Minute)//5 Brake Map (0=None, 1=Left, 2=Right)//6 Wheel Radius (feet)//7 Steer Angle (degrees)//8 Static Compression (feet) (0 if rigid)//9 Max/Static Compression Ratio//10 Damping Ratio (0=Undamped, 1=Critically Damped)//11 Extension Time (seconds)//12 Retraction Time (seconds)//13 Sound Type//14 Airspeed limit for retraction (KIAS)//15 Airspeed that gear gets damage at (KIAS)&l;contact_points&r;point.0=1, 40.00, 0.00, -8.10, 1181.1, 0, 1.442, 55.92, 0.8, 2.5, 0.9, 4.0, 4.0, 0, 0.0, 0.0point.1=1, -7.75, -8.58, -8.68, 1574.8, 1, 1.442, 0.00, 1.0, 2.5, 0.9, 6.9, 6.9, 2, 0.0, 0.0point.2=1, -7.75, 8.58, -8.68, 1574.8, 2, 1.442, 0.00, 1.0, 2.5, 0.9, 7.1, 7.1, 3, 0.0, 0.0point.3=2, -14.17, -47.33, 0.00, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 5, 0.0, 0.0point.4=2, -14.17, 47.33, 0.00, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 6, 0.0, 0.0point.5=2, -54.00, 0.00, 2.83, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 9, 0.0, 0.0point.6=2, 42.67, 0.00, -3.75, 787.4, 0, 0.000, 0.00, 0.0, 0.0, 0.0, 0.0, 0.0, 4, 0.0, 0.0max_number_of_points=21static_pitch=0.62 //degrees, pitch when at rest on the ground (+=Up, -=Dn)static_cg_height=7.66 //feet, altitude of CG when at rest on the ground