Originally Posted by
zvezda
On most airlines, C fares are fully changeable, fully refundable walk-up fares, while Z fares are typically non-changeable, non-refundable, advance-purchase fares. This is the case with SQ.
Mostly true, however, SQ uses Z as the prime booking codes for LAX/EWR-SIN nonstops. Those are the most flexible fares on those routes.