It was flight 447. https://en.wikipedia.org/wiki/Air_France_Flight_447
IMO The mystery of MH370 is partially due to some incorrect assumptions, which can't be proven or disproven until the main wreckage is found, and/or the blackboxes recovered.
Where the wreckage ended up could depend several factors. eg. glide ratio of a 777 (~18:1), or how the 777 Fly-by-wire control system works under certain failure modes. There hasn't been a crew incapacitation crash in a fly-by-wire airliner before.
A small fire in the electrical bay could disable aircraft systems in unexpected ways, and possibly even burn out on its own, and the damage doesn't actually cause the jet to crash immediately. If the cockpit crew were incapacitated at cruise altitude, the jet could still end up 100 miles away from the point the engines flamed out.