If the obstacle on the approach route is eight meters tall and the obstacle on the departure route is ten meters tall, what is the unusable space for the departure route?

The calculation of unusable space for the departure route is fundamentally based on the height of the obstacles encountered. In this case, the departure route has an obstacle that is ten meters tall. According to air assault operations, when calculating the unusable space, you typically apply a multiplication factor to the height of the obstacle to determine how much vertical clearance is needed for safe passage.

For obstacles, it's common practice in aviation to use a multiplier of 10 times the obstacle height to estimate the necessary buffer zone. Thus, for a ten-meter obstacle, the unusable space calculation would be:

10 meters (obstacle height) x 10 = 100 meters.

Therefore, the unusable space for the departure route is accurately calculated as 100 meters, which corresponds with the correct answer. This calculation ensures that the helicopter or aircraft has the adequate clearance needed to operate safely in relation to the height of obstacles.