Small birds molt once or twice a year, and they replace their 9 or 10 primary flight feathers a few at a time over the course of a few weeks.

小型鸟类一年进行一到两次换羽，在换羽期间，它们一次会替换掉9到10根左右的飞羽，而这个过程将持续几周时间。

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Small birds molt once or twice a year, and they replace their 9 or 10 primary flight feathers a few at a time over the course of a few weeks.

形体小的鸟儿一年脱羽一到两次。它们有9到10只主要用于飞行的羽毛，鸟儿们一次更换几只，在几周的时间内它们就可以完成更换。

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The paper also describes a ground demonstration of a one channel primary flight control system and a flight demonstration of an aileron trim control system.

同时还介绍了一单通道主飞控系统的地面演示和一副翼配平控制系统的飞行演示。

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"The captain said, at that point, he looked at his primary flight display for an ETA and realized that they had passed" the airport, it added.

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