Several episodes break from the formula to varying degrees -- "Last Salute To The Commodore," for example, was a true "whodunnit" -- but the 2 episodes that stand out as the biggest departures from the familiar "Columbo" formula are "Undercover" and "No Time To Die".
Both of these were adapted from police novels by popular writer Ed McBain (actually a pseudonym -- you might have read that he recently died), so the stories were not originally written for "Columbo". Most "Columbo" fans would, at their most charitable, say that these 2 episodes were, um, an experiment that failed. If anything, they prove that the forula was well worth keeping.
Here is a direct link to the article "Ed McBain's Columbo", which can be found in the Scrapbook area of the site: