David Bentley's letter (Flight International 29 October-4 November re-states that "a four-engined aircraft suffering an engine failure will have to divert exactly as often as a two-engined aircraft". This is not so.

After an engine failure in a multi-jet aircraft (more than two) with no further complications, the flight may proceed as a normal operation. It is not an emergency and does not require a diversion. However, reduced performance considerations may require a diversion particularly if destination weather is not forecast to be good or if terrain causes a significant deviation from planned route.

In a twinjet, an engine failure is an emergency and the flight must land ASAP.

Trevor Brown, Banbury, UK

Source: Flight International