A. 飞机下午一点就起飞了，上午十点他们才去机场。√ If you decide to go to the airport at 10:00 am and you live far away from the ariport, and it would take you nearly about 2 to 2 and a half hours there, you can say like this. It often means that 'they start going there too late.' B. 飞机下午一点才起飞，上午十点他们就去机场了。√ If you decide to go to the airport at 10:00 am and you live close by the airport, and it would take you only 10 minutes to 20 minutes there, you can say like this. It's a different tone to the first sentence.

Both Ok,but different meaning. A. 飞机下午一点就起飞，上午十点他们才去机场了。（语气有点责怪他们太晚去机场候机了) B. 飞机下午一点才起飞，上午十点他们就去机场了。（讲话的人觉得他们去机场过早了）