The recent flurry of letters on the age-old debate between four engines or two has thrown up some amusingly unrealistic arguments given the reality of 21st century airline operations.

The most recent "Four engines are simply better" (Flight International, 1-7 October) is fundamentally incorrect. Using this logic, we should immediately begin strapping on as many engines as will fit under a wing.

From an engineering and "failure driven divert" point of view, four engines are more complicated, not simpler, with twice the opportunity for a failure. A four-engined aircraft suffering an engine failure will have to divert exactly as often as a two engined aircraft.

When jet engines were less sophisticated, the two versus four argument would have tilted in favour of four for safety. These days, given the incredible reliability of modern aero engines and the abilities of flight-control computers, the four-engined argument is becoming spurious, with the exception of the 180min rule. In the real world, two engines win every time.

David Bentley Sydney, Australia

Source: Flight International