INSTRUMENTS FLIGHT PLANNING
At 0900, you notice during your scan that the No. 2 needle is spinning and the DME is not
functioning. There is no station IDENT. The last DME readout you had was 50 DME. Now the
pilot wants to know when to turn.
Your action is:
Determine ETA at MCN
GS = 360 kts (6 NM/min)
Distance to turnpoint = 50
ETE = 8 min
ETA = 0908
Heading is maintaining course so no change is necessary.
What you have just done is perform DR. Based on all the information available, you have
predicted when the aircraft will mark a turnpoint. There is no physical indication that you are at
MCN, only your ETA will provide you an estimate.
As long as you have a GS, you can predict where the aircraft is over any distance.
Continuing the example, your route of flight has the aircraft MARK-ON-TOP MCN, then
proceed to Alma (AMG) via J45. The pilot needs to know what heading to fly and what the ETA
is to AMG (Figure 3-3).
The simple thing would be turn to 139º, the outbound course from MCN, at 0908. This does not
account for any wind; therefore, the aircraft does not maintain course.
It is absolutely critical that the wind is calculated and accounted for, before making the turn at
TAS = 300 kts
GS = 360 kts
CRAB = 5° right (083° for 078°)
Plotting on the CR-2 yields a wind vector of 235°/65 kts.