There have been numerous air carrier accidents in which the crew attempted takeoff without the leading and trailing edge flaps extended to the takeoff position. Unlike many general aviation airplanes, large turbojet aircraft require high-lift devices (leading and trailing edge flaps and slats) for the airplane to safely get airborne. In some of these accidents, the Takeoff Warning System (TOWS) was intentionally disabled, preventing the crew from receiving a warning of incorrect airplane configuration.
Here are notable accidents resulting in 746 fatalities:
1974 Lufthansa flight 540, B747, 59 fatalities
1987 Northwest 255, MD 82, 150 fatalities
1988 Delta 1411, B727-200, 14 fatalities
1999 LAPA Flight 3142, B737-200, 65 fatalities
2005 Mandala Airlines 91, B737-200, 144 fatalities
2008 Spanair 5022 - MD 82, 154 fatalities
In every case, if the flight crews had performed their normal pre-takeoff checks, the accidents would have been averted. It is essential that all crew members actually confirm every item on the appropriate checklist.
As an additional mnemonic, many pilots will perform a FEATS check before every takeoff: Flaps, EPRs, Airspeed bugs, Trim, Speed brake.