Takeoff and Departure Phase
Speeds and the decision to reject
V1 is the decision speed: above it, a rejected takeoff is generally more dangerous than continuing. Vr produces the pitch attitude needed to reach V2 by 35 ft; V2 guarantees the required single-engine climb gradient. Vmcg (ground) and Vmca (air) bound directional control, and balanced field length is where accelerate-stop distance equals accelerate-go distance. Questions frequently ask which speed remains valid if a runway is shortened - the answer is that field length limits may reduce V1, never increase it.
Wake turbulence and departure path
Wake turbulence avoidance is a favorite: rotate before the preceding aircraft's rotation point, stay above its flight path, and fly slightly upwind of the vortex pairs. For a departing heavy jet, wake vortices sink and drift with the wind - a light crosswind makes the upwind offset especially important.
Climb gradients
The standard instrument departure requires 200 ft/NM (about 3.3%) unless published otherwise, and obstacle departure procedures are often steeper. Convert gradient to rate of climb by multiplying the percent gradient by groundspeed: rate (fpm) ≈ gradient (%) × groundspeed (kt).
Worked example: A departure requires 400 ft/NM at 140 kt groundspeed. First convert: 400 ÷ 6,076 ft per NM ≈ 6.6%. Then 6.6 × 140 ≈ 920 fpm required. If the aircraft cannot make that, a different departure or a departure alternate is needed.
Rule of thumb: 200 ft/NM ≈ 3.3%; percent gradient times knots is your required feet per minute.