Once did ZAG-MAD and that was around the 4 hr mark. 146-300 could hit FL310 whereas the -100/-200 were FL290 limited from memory. Could not enter RVSM airspace due to the altimetry system originating from a sopwith camel! Aircraft without the TGT roll back (eng a/ice valve mod) being incorporated were limited to FL260 in icing conditions.
Still a pretty decent aircraft but it did keep us engineers busy, great for contracting though....lots of overtime!