"Unexpected heat, cold, wind, rain, hail, high or low ... pressure regions, or other meteorological conditions," according to the patent document.
"High winds may make it difficult or impossible to control the flight operations. High heat may also result in failure or malfunction of the battery ... leading to loss of thrust provided by the rotor system. Other components ... such as the rotor system, flight control computer, flight sensors, or other components, can unexpectedly malfunction or fail for various reasons."
The idea behind the patent is not to let the drone dismantle itself until there's nothing left.
"During the fragmentation sequence, one or more parts or components of the UAV can be released. In doing so, the weight, speed, air drag coefficient, and other factors related to the UAV can be altered. At the same time, the momentum and trajectory of the UAV are also altered.
"According to aspects of the embodiments, the fragmentation sequence is tailored to modify or alter the manner in which the UAV descends, to control the descent in a preferred, controlled manner," the patent document says.
The drone's systems would allow it to control where the parts fall, so they would "descend in a calculated or estimated trajectory to the preferred locations."
The illustration accompanying the patent indicates those locations would include a pond and a tree. The drawing also appears to show the drone dropping the cargo into a tree.
Parts could be released using latches, hooks or springs, or "small explosive charges" or compressed gas.
There's attention to cost, among other factors, in what gets jettisoned.
"The fragmentation sequence engine can select the order based on various factors, such as the replacement value or cost of the components, the air drag coefficients of the components, the weight of the components, the purpose of the components, and other factors," the patent document says.
However, just because Amazon patented this system -- which also seems unsuitable for urban centers -- that doesn't guarantee it'll go into action. Still, the company recognizing the possibility of "catastrophic failure" of a delivery drone indicates that some solution is needed before Amazon starts delivering goods via drones.
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