The Navigational Computer is needed in the exam and can be used for pre-flight planning, but there is no place for it in the cockpit! Instead, we use Mental Dead Reckoning while airborne to simplify a lot of the calculations.
The Maximum Drift technique is not required for the exam but it is very useful for practical in-flight navigation.
Pre-flight we can calculate a number that is the maximum drift the aircraft will experience – i.e. the most it will be ‘blown off course’. This depends on the wind speed & the aircraft’s true airspeed. It can be calculated with the formula:
For example, if your aircraft’s cruise speed is 90 knots and the wind speed is 20 knots:
So in this case, the most the aircraft will drift due to the wind is 13° (unless the wind speed or aircraft airspeed changes).
The aircraft won’t always drift by the maximum drift amount.
However, when the wind is somewhere between these two, we need to calculate headwind/tailwind and crosswind components – this is covered in the next two lessons.