Instrument Rating Math

Question 1

Calculating lead intercepts for DME arcs

Answer 1

Groundspeed / 200

Question 2

Calculating Rate of Descent to Track Glideslope

Answer 2

(Groundspeed / 60) x 300

Question 3

Initiating level-off from climb or descent

Answer 3

10% of Rate of Climb/Descent

Question 4

Converting climb gradient from feet per nautical mile (NM) to feet per minute (FPM)

Answer 4

Groundspeed / 60 x Feet Per NM

Example: DP requires 300 ft/NM climb.
Your ground speed is 120KT, which is 2NM per minute (120 KT / 60 min = 2 NM per minute).
300 x 2 = 600 FPM

Question 5

How far to start a decent (assuming 3 degree glide path)

Answer 5

Altitude to lose / 300
Example: 6000’ to lose, start descent 20 NM out.
(6000/300 = 20 NM)

Question 6

Calculating Visual Descent Point (VDP) for a 3 degree glideslope - Distance

Answer 6

Height Above Touchdown (HAT) / 300

Example:
HAT/MDA is 430 ft. AGL.
430/300 = 1.4nm

Question 7

Calculating Visual Descent Point (VDP) for a 3 degree glideslope - Time

Answer 7

Subtract 10% of the MDA (HAT) from the time between FAF and MAP

Example:
MDA is 430 ft. AGL
Time between FAF and MAP is 3:54
10% of 430 = 43
Subtract 43 seconds from 3:54 = 3:11 to VDP/PDP

Question 8

Standard Rate Turn

Answer 8

360 degrees = 2 minutes

Question 9

Half Standard Rate Turn

Answer 9

360 degrees = 4 minutes