In any system where a function is dual-redundant, and the redundancy has
no resulting downside, it is obviously true that the probability of a failure of the whole system is reduced.
So a twin should be less likely to go down
per airborne hour than a single.
On top of that most ME failures of an engine that happen during cruise go unreported and will never appear in any stats, which results in ME forced landings to be over-represented, again per airborne hour.
Unfortunately reality interferes with this, and the key is the "no resulting downside" bit.
And there are several downsides:
- EFATO scenarios require a high degree of pilot currency
- More complex fuel systems; in some cases you can be drawing fuel from one tank while the gauge(s) show the contents of a different tank
- Higher operating cost, resulting in reduced pilot currency
- Higher operating cost, resulting in less picky attitudes to maintenance because you carry a spare engine (you can tell I like to avoid controversy
)
- Most twins are > 1999kg so there is a big incentive to file "VFR" to avoid the IFR route charges (this is an awfully persistent trend in ME CFITs)
- Most twin types have been out of production for decades, and their age makes maintenance to any particular standard more expensive
One might also think twins fly more hazardous missions, which will further skew the stats against them. I am not sure whether this is true today; the pilots who I know who fly what I call light twins do not fly in conditions any more hazardous than SE pilots I know of similar experience. There are also plenty of deiced singles flying around, which equipment-for-equipment are a match for any light twin. 2 engines do not alone deliver any specific capability w.r.t. weather.
Those who don't like my posts don't have to read them. Contrary to popular belief, there is no requirement to be on the internet to correct every perceived instance of somebody having written something one disagrees with
