Complex sentence: Instead of taking on 20,088 litres of additional fuel that they required, they actually took on only 4,917 litres, giving them a total fuel load of 10,100 kg, about half the amount required to reach their destination.
Split into simpler sentences: Instead of taking on the 20,089 litres of additional fuel they required, they actually took on only 4,917 litres. This error gave them a total fuel load of 10,100 kg, 45% of the amount required to reach their destination.