Included in the "dull" and the "difficult" categories were surveillance missions requiring time and a degree of persistence that crews of manned aircraft could not provide.
“枯燥”“困难”分类内的任务包括需要时间和相当程度的耐久性的监视任务，这是人工飞行器不能满足的。
2
Work hours management is divided into four parts: work categories, statistics, data processing, feedback of results, and permeates in all aspects of the aircraft maintenance production organization.
工时管理分为工时分类、数据统计、数据处理、结果反馈四个部分，渗透于飞机维修生产组织的各个环节。
3
In general, the control methods of the aircraft 's landing gear shock absorbers are classified three categories: a passive type, an active type, and semi - active type.