Descent/holding

Question 1

What speed should be flown to achieve the minimum descent gradient?
What about lowest RoD?

Answer 1

For a given weight, the magnitude of the descent gradient is minimum when drag is minimum (best L/D), hence the green dot speed.
For a given weight RoD is lowest when TAS x D is lowest

Question 2

How does a decrease in altitude affect RodD/gradient of descent?

Answer 2

As density increases as altitude decreases, drag will increase. As both RoD/gradient are proportional to drag, their magnitude will increase.

Question 3

How does change in temperature affect RoD/gradient?

Answer 3

Is insignificant because you could conclude as air warms at a set altitude, density reduces and so drag will therefore reduce. However in a descent at constant IAS/M, warmer air means a higher TAS which offsets this.

Question 4

How does weight affect RoD/gradient?

Answer 4

L=Wcosy=1/2Clpv^2S
At a given TAS a higher Cl is required to maintain lift so is achieved by increasing AoA… which reduces descent gradient.
RoD:TASy
So it can be seen with a constant TAS that RoD decreases at higher weights when y decreases.

Question 5

How does wind affect RoD/gradient, fuel/time to BOD and distance to BOD?

Answer 5

A HWC will:

• Increase flight path angle (gradient)
• Decrease ground distance
• NIL RoD
• NIL fuel/time to BOD

Question 6

What 4 types of descent speeds are there?

Answer 6

Minimum gradient, minimum rate, minimum cost, emergency descent.

Question 7

Describe a descent at minimum gradient

Answer 7

Also known as a drift down, it descends at the green dot speed. It allows the highest possible altitude to be maintained over the longest distance.
Day to day is operationally ineffective, useful if engine failure over mountainous terrain.

Question 8

Describe a descent at minimum rate

Answer 8

The speed is lower than GD (minimum gradient) and is really only useful when required to extend time in air in case of engine failure.

Question 9

Describe a descent at minimum cost

Answer 9

CI=0 descent green dot speed (L/D)/Mmr

CI=max descent at VMO-10kt or MMO-0.05

Question 10

Describe an emergency descent

Answer 10

Descent at VMO/MMO to FL100 ASAP.

Is the greatest RoD and can use air brakes to increase.

Question 11

What is the cabin pressure just before landing?

What is the default/max cabin repressurisation?

Answer 11

AD pressure + 0.1PSI

Default set to 350ft/min, max 750ft/min

Question 12

What purpose is a repressurisation segment?

Answer 12

If the cabin descent is longer than the a/c descent, a repressurisation segment is required. This is where the vertical speed of the a/c is limited to the cabin repressurisation initially ensuring this never occurs… cabin alt>ambient alt

Question 13

What speed should be flown in a hold?

Answer 13

Green dot speed