Strong crosswinds, low visibility, damage to the airplane, or unresponsive instruments or controls greatly increase the danger of performing a belly landing.
However, some pilots neglect these checklists and perform the tasks by memory, increasing the chances of forgetting to lower the landing gear.
Even careful pilots are at risk, because they may be distracted and forget to perform the checklist or be interrupted in the middle of it by other duties such as collision avoidance or another emergency.
In small aircraft this most commonly takes the form of a warning light and horn which operate when any of the landing gear is not locked down and any of the engine throttles are retarded below a cruise power setting.
In other cases, pilots cannot hear the horn on older aircraft due to wearing a modern noise-canceling headset.
Most airliners incorporate a voice message system which eliminates the ambiguity of a horn or buzzer and instead gives the pilot a clear verbal indication: "GEAR NOT DOWN".
The combination of advanced warning systems and effective crew training has made gear-up landing accidents in large aircraft extremely rare.
Multiple redundancies are usually provided to prevent a single failure from failing the entire landing gear extension process.
A German Junkers Ju 88 bomber, after an attack on Soviet shipping in April 1942, was abandoned by its crew and came down on a hillside at Garddevarre in Finnmark in the far north of Norway.
[4] On 27 September 1956 a Bell X-2 experimental aircraft, after establishing an airspeed record of Mach 3.2, landed unmanned in the desert after a series of stalls and glides.
[5] Possibly the most well-known is a United States Air Force Convair F-106 Delta Dart, tail number 58-0787.
Following the pilot ejecting, the aircraft's spin stabilised, and the Delta Dart proceeded to fly for several miles until it came down in a field near Big Sandy, Montana.
[9] On 8 May 2006, a United States Air Force B-1 Lancer strategic bomber landed on the atoll of Diego Garcia in the Indian Ocean without lowering its undercarriage.
The plane crashed into a densely populated residential area near Karachi Allama Iqbal International Airport, killing 97 of 99 people aboard, as well as one on the ground.
The aircraft failed to stop on the runway, hitting a raised earthwork embankment and bursting into flames, killing 179 out of 181 onboard.