السلام عليكم When going on a plane to jeddah for umrah, if your on an airline that may not announce the crossing of the miqaat, can you utter the intention for umrah beforehand? Also do you need wudhu when you cross the miqaat and start umrah?

This is not uttering the intention. Uttering the intention is bid'ah, even in Hajj and Umrah. You are simply entering into the nusuk. If I said "Allahu Akbar" as the Takbirat al-Ihram for the Salah, would I say I said my niyyah out loud? No, I didn't, because doing so is bid'ah. The same thing applies when you say "Labbayka Umratan"; it is just like saying "Allahu Akbar" as an entry into this act of worship. Saying it before the Miqat is correct, but it is not the Sunnah. The Sunnah is that you say it at the Miqat or a little bit before it. Because you are in an airplane, you will pass through the Miqat in a very short time. If you say it 10, 15, or 20 minutes before, insha'Allah there is no problem. Even if you said it earlier than that, it is still valid; however, it is not the Sunnah. The Sunnah is to say it at the Miqat or a little bit before. What is safer for you, since you are in an airplane, is to say it slightly before so that you do not pass the Miqat. You can also ask the crew on the airplane to tell you when you are approaching the Miqat.