An aircraft flies from A (S22°50’ 028°33’) to B (S19°30’ E028°33’) at a groundspeed of 110 kt. What is the flight time?
Refer to figure.
Calculate the distance
Since the longitude for both positions is the same, the aircraft is travelling along a meridian, resulting in a change in latitude. Therefore,
Step 1: Calculate the change in latitude
- For different hemispheres, we add the two latitudes together.
- For same hemispheres, we subtract the smaller latitude from the larger one.
Since both positions lie in the Southern Hemisphere, we will subtract the latitudes. Therefore,
- Change in latitude = S22°50' - S19°30'
- Change in latitude = 3°20'N*
* We are travelling northwards to a lower latitude, which is why 'North' is indicated.
Step 2: Calculate the distance
A change of 1° in latitude corresponds to a distance of 60 NM.
- Distance (NM) = change in latitude x 60 NM
- Distance = 3°20' x 60 NM
- Distance = 200 NM
Calculate the flight time
Once we have calculated the distance, flight time can be calculated using the following formula:
- Flight time (hr) = Distance (NM) / Groundspeed (kt)
- Flight time = 200 NM / 110 kt
- Flight time = 1 hr 49 min
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