An overweight landing is defined as a landing made at a gross weight in excess of the maximum design (i.e., structural) landing weight for a particular model.
Sometimes, a situtation (e.g. an engine failure) may arise that requires the airplane to land soon after take off. In such a case, the pilot needs to choose between two basic options:
Land at a weight (considerably) above the maximum design landing weight. This would lead to shorter time in the air, but may lead to further damage to the aircraft and has a greater potential to turn the landing into a runway excursion.
Reduce the weight before landing. There are two ways to do this:
Execute a holding pattern to burn fuel. This option is somewhat close to normal operations but means that the aircraft will stay in the air longer.
Dump (jettison) fuel. This allows quick landing within the operational limits but may impact other aircraft or people on the ground.
Before choosing overweight landing as the preferred option, the pilot needs to consider the following aspects of the situation:
Regulatory. Generally, maximum landing weight is an operational limitation to be complied with. However, a deviation from this rule is possible in the interest of safety. Examples of such situations include:
A malfunction rendering the aircraft unairworthy
A situation where an expeditious landing would reduce the exposure to a hazard
A situation requiring immediate medical attention
Safety. Reducing the aircraft weight (regardless of the option chosen) requires additional time. This increases the risk of further deterioration of the situation. On the other hand, an overweight landing would reduce the performance margins.
Ecological. Dumping fuel is generally undesirable at levels below 5000-6000 feet (above these heights the fuel would evaporate before reaching the ground).
Airplane structural capability. While the maximum landing weight is an operational limitation, the aircraft components (especially the landing gear are designed to sustain much higher loads than would occur during typical landings.
Airplane performance capability. The AFM typically provides landing performance data at weights significantly above the maximum design landing weight and can be used in conjunction with landing analysis programs to calculate landing performance. Also, pilots need to balance between the application of maximum braking and making use of the landing runway available so that brake energy limits are not exceeded.
Automatic landings. Generally, while automatic approach can be attempted, it is recommended that the landing is performed manually.
Inspection requirements. Generally, a special inspection is required after an overweight landing, regardless of how smooth it was. Additional maintenance or repair action might be necessary as well.
While all three procedures (burn fuel, dump fuel, land overweight) are considered safe, it is the pilot's task to assess the factors above and choose the optimal one for the particular situation.