TM 1-1510-262-10
2. Determine the total height required to clear the obstacle by adding to the obstacle height the decrease
in aircraft altitude during the takeoff procedure due to a downhill runway gradient.
1.9% gradient 5069 ft = 96.3 feet = 96 feet
The total height required to clear the obstacle is: 88 ft + 96 ft = 184 feet.
3. Obtain the required gradient to clear the obstacle from the Distant Takeoff Flight Path graph using the
obstacle distance from reference zero found in step 1., and the total height determined in step 2.: 1.19%.
4. Read the scheduled net gradient of climb from the Net Takeoff Flight Path-Second Segment - Flaps
Approach graph (Fig. 7-30): 2.53%.
Thus, the calculations indicate that a takeoff weight of 16,000 pounds will result in a net climb gradient
greater than that required to clear the obstacle, even if an engine should fail at the most critical takeoff
point.
(2)
Example 2-Obstacle clearance above 500 feet: given:
Obstacle Height Above Aircraft at Brake Release
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 600 feet.
Obstacle Distance from Brake Release . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.71 nm
1. Obtain the accelerate-go distance to 50 feet AGL . . . . . . . . . . . . . . . . . . . . . . . . 5069 feet (0.83 nm).
2. Read the scheduled distance from the Horizontal Distance From Reference Zero To Third Segment
Climb - Flaps Approach graph (Fig. 7-31) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.07 nm.
3. Add the results of steps 1. and 2. to obtain total distance to start of third segment climb, (0.83 nm +
5.07 nm) = 5.9 nm.
4. Distance to obstacle from start of third segment climb is obtained by subtracting results of step
3. from 10.71 nm. (10.71 - 5.9) = 4.81 nm.
5. Add to the obstacle height above the aircraft at brake release any decrease in aircraft altitude
during the takeoff resulting from a downhill runway gradient.
The sum is the total height required to clear the obstacle:
(1.9% gradient / 100) x 5069 ft = 96.3 feet = 96 feet
The total height required to clear the obstacle is: 600 ft + 96 ft = 696 feet.
6. Required climb gradient to clear obstacle is obtained using the following formula:
% Gradient = (RH) x (F) / (D)
Where:
RH = Required Height (in feet) above 500 feet
F = A units conversion factor of 0.0165
D = Distance (in nautical miles) to obstacle from start of third segment
Therefore:
% Gradient = (696 - 500) (0.0165) + 4.81 = 0.67%
7. Obtain (from the Net Take-Off Flight Path - Third Segment graph, Fig. 7-34) the scheduled third
segment net gradient of climb of 2.33%. Since this gradient exceeds the required gradient of
0.67%, the calculations indicate that the obstacle will be cleared at a takeoff weight of 16,000
pounds even if an engine should fail at the most critical takeoff point.
7-17
