Fatal is an adjective which means (1.) deadly, causing death (2.) decisive, important in outcome (3.) disatrous. Fatal implies death, whether of a human, cause or idea. A fatality is a person who was killed by accident, disease or war. Fated is an adjective which means doomed. Fatalism is a philosophy dating from the 1670s that states that all things are determined by fate, one is helpless to change events. An adherent of fatalism is a fatalist. The word fatal arose in the fourteenth century to mean decreed by fate, from the Latin fatalis meaning ordained by fate, decreed, destined. In the fifteenth century, fatal came to mean causing death or disaster.
Fateful is an adjective which means (1.) having important consequences (2.) controlled by fate (3.) prophetic. The word fateful merely implies something which turned out to have momentous implications, good or bad. The adverb form is fatefully, the noun form is fatefulness. Fateful first appears in the early eighteenth century to mean prophetic, of momentous consequences, it comes from the Latin fatidicus, which means prophetic.
Examples
Time Warner Cable must pay nearly $6 million as part of a lawsuit alleging it was largely responsible for a fatal natural gas explosion that leveled an upscale Kansas City restaurant, jurors ruled Thursday. (The Kansas City Star)
Woman held over fatal knife attack on husband in Bukit Panjang flat (The Straits Times)
The moral of this story needs to be remembered: Americans do not just sit there and wait to become victims when we’re attacked, any more than our sailors and airmen at Pearl Harbor did as the first Zeroes cleared the horizon on another fateful day — Dec. 7, 1941. (The Register Guard)
As the knuckles turn white when the fateful day of a Fed hike arrives, remember that bull markets end after the last rate hike not the first one. (The Financial Post)