1.The faster a helicopter goes, the greater the difference and the more difficult it is to maintain level flight.
而直升机飞得越快，这种差异就越显著，也就越难于维持水平飞行。
2.CONTROLLER: "American 11, Boston Center, roger, climb, maintain level two eight zero. "
美航11号航班，这里是波士顿控制中心，收到，继续攀升并维持在280区域。
3.This difference in lift can make it hard to maintain level flight.
这种差异能够产生保持直升机水平飞行的升力。
4.The aircraft is lost control now , I can not maintain level flight at present altitude .
飞机现在失去操纵，我在现在的高度上不能保持平飞。