Talking about my own puddlehopper here, rather than a grown up aeroplane, I always do a thorough visual before washing it. Dirt is a superb developer for the grease that secretes in fatigue cracks.

Once I've found a gearbox close to departing the aircraft, and on another occasion an intake filter bracket with a fatigue crack. Neither problem was easily visible on a clean aircraft.

G

I remember hearing that aircraft should be coated in a thin film of Cod Liver oil after cleaning, for maximum efficiency (no sh*t, that's what I heard)

Any truth to this?

I must say Fast Jets comments about KLMuk rings a bit true. The ones at Manchester do appear to be grubbier than other airlines.It's probably the paint sceme showing it up more!!