3 / 20

Given:

CAS: 190 kt
Altitude: 9000 ft
Temperature: ISA -10° C
True Course TC: 350°
W/V: 320/40
Distance from departure to destination: 350 NM
Endurance: 3 hours
Actual time of departure: 11:05 UTC

The Point of Equal Time PET is reached at:

• A
12:21 UTC
• B
12:33 UTC
• C
12:13 UTC
• D
12:03 UTC

Refer to figure.
(1) First, we must calculate TAS using the Flight Computer so we can then calculate GS:
ISA temperature at 9 000 ft = 15 - 2 x 9 = -3º; if actual temperature = ISA - 10ºC, then actual temperature = -13ºC.
On your flight computer, on the "AIRSPEED" window, align 9000 ft with -13ºC.
On the Inner ring, look for CAS 190 kt and read the corresponding TAS value of approx. 214 kt.

(2) Now, that we know our TAS - we can calculate our GS using TAS and Wind:

Solving from Heading (HDG) & Ground Speed (GS), knowing WV, TAS and required track.

1. Set wind direction to 320º under the "TRUE HEADING" index at the top.
2. Set the center point on the True Airspeed (TAS) of 214 kt.
3. Mark the wind velocity 40 kt down from the centre point.
4. Initially, set the True Track under the "TRUE HEADING" index.

• GS home: 170º
5. Note that this heading would result in 5ºL drift and a track of 165º.
6. Reduce the heading value under the index until the heading minus the drift gives a track of 170º. This occurs at a heading of 175º with 5ºL drift.
7. The groundspeed for this track is approximately 248 kt.
• GS out: 350º
5. Note that this heading would result in 7ºR drift and a track of 357º.
6. Reduce the heading value under the index until the heading plus the drift gives a track of 350º. This occurs at a heading of 343º with 5ºR drift.
7. The groundspeed for this track is approximately 178 kt.

(3) We can now apply the formulas:
Distance to PET = (GS home x Distance) / (GS out + GS home)
Distance to PET = (248 x 350) / (178 + 248)
Distance to PET = 203.8 NM

Time to PET = Distance to PET / GS out
Time to PET = 203.8 NM / 178 kt = 1 h 08 min

(4) PET is reached at = Time of Departure + Time to PET = 11:05 + 1:08 = 12:13

Your Notes (not visible to others)

This question has appeared on the real examination, you can find the related countries below.