Performance desk · clear the diversion
Use net stabilising tables and a drift-down profile to test terrain, fuel and time.
Does the supplied drift-down profile clear this route?
Enter the correct engine-out table with the relevant mass, pressure/temperature condition, bleed/anti-ice and speed schedule. Establish whether the altitude is gross or net. If it is already net, do not subtract another en-route decrement. Compare the net stabilising altitude with the obstacle elevation plus the applicable clearance requirement using a consistent datum.
Read the net stabilising level
Enter the correct engine-out table with the relevant mass, pressure/temperature condition, bleed/anti-ice and speed schedule. Establish whether the altitude is gross or net. If it is already net, do not subtract another en-route decrement. Compare the net stabilising altitude with the obstacle elevation plus the applicable clearance requirement using a consistent datum.
To find a maximum terrain-limited mass, reverse the table: start at obstacle elevation plus the required margin, find the corresponding mass by permitted interpolation, and compare it with other limits. The most critical terrain is within the actual accountability area, not necessarily the highest peak on the map.
Read the transient profile too
A safe level-off point does not prove the preceding descent passes every obstacle. Use the drift-down graph for the stated starting level, mass and conditions to read elapsed time, air distance and fuel to each altitude. Convert air distance to ground distance with the applicable wind method; a constant-wind exercise can use ground distance = air distance + wind × elapsed time.
Account for any charted deceleration segment and fuel burn. Update mass only where the data method permits. Compare each net path point with terrain; verify the diversion is reachable with the required fuel and can meet landing/approach limits. An exercise that asks for fuel, time and distance needs all three, not just the final level.
Can you make the performance decision?
Four original questions. Work from the stated conditions and review the reasoning.