Assalam Alaikum. Whatever brother Abdullah90 wrote is absolutely correct. Because, the plane crosses the miqaat in air. And miqaat can not be crossed unless you are in Ihram. Therefore making niyaah and getting yourself in Ihram is necessary, before the plane crosses miqaat. However, once you are in Makkah, and you want to perform another umrah, then Masjid Ayesha is the miqaat for you. Also, it is more virtuous to perform tawaaf, rather than doing additional umrah.