Descent and Holding

Question 1

For a given weight, what aerodynamic configuration will give minimum descent gradient? What speed is this?

Answer 1

When drag is minimum or L/D is maximum

green dot speed

Question 2

For a given aircraft weight, what aerodynamic configuration will give minimum rate of descent?

Answer 2

TAS*drag is minimum

Question 3

What is the equation for determining gradient of descent?

Answer 3

γ = (Thrust - Drag) / Weight

Question 4

What is the relationship between min RoD speed and max glide range speed?

Answer 4

Min RoD is lower than Max glide range speed

Question 5

What speed should be flown for min RoD and for min descent gradient (γ)?

Answer 5

Min RoD: min TAS*Drag (less than Green Dot)

Min γ: best L/D ratio (Green Dot)

Question 6

Is min gradient normally used?

Answer 6

No

Question 7

How does Pressure altitude and Temperature affect RoD and descent gradient?

Answer 7

Not possible to conclude either

Question 8

How does Weight and HWC/TWC affect RoD and descent gradient when descending in the standard speed range?

Answer 8

Increase Weight: Decrease RoD and gradient

HWC: constant RoD, Increase angle
TWC: constant RoD, decrease angle

Increased weight requires higher CL, achieved by higher AoA and lower gradient. RoD is function of gradient so it also decreases

Question 9

What is the standard thrust rating for a descent? what about if a depressurisation segment is required?

Answer 9

Flight Idle thrust

Adapted thrust if depressurisation segment is required

Question 10

What speed should be flown for a low cost index compared to a high cost index?

Answer 10

CI low: Minimum descent speed (actually below green dot but operationally green dot or higher is most beneficial)
CI high: V(mo) - 10kts

Question 11

How does the cabin of an aircraft descent compared to the actual aircraft? What happens if actual descent time is less than required for the cabin?

Answer 11

Cabin will descent at 350-750 ft/min to be +0.1psi higher than atmospheric at the destination
If aircraft descent time is calculated to be less than the cabin, the initial descent must be with power on to limit the V/S and extend the descent time to equal the cabin descent time

Question 12

What speed should be flown in a hold to minimise fuel flow? Aerodynamic vs operational?

Answer 12

Actual: somewhere between min drag speed and max L/D ratio
Operational: green dot

Question 13

What speed should a hold be flown at?

Answer 13

Green Dot (approximating min drag)
ATC assigned speed
Max speed shown in AIP