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I am a US citizen holding multiple passports. The problem is that my US passport is getting very full despite having 6 more years on it. There are Visas on my passport which I do not want to lose when I get a new passport. I will be traveling to few countries and was thinking of using my non-US passport to exit the country. My intent is to ration my US passport usage. I also know a US Citizen must have US passport to enter and exit the country. Entering is a "no duh". Exiting.. well, we don't have exit checks in the US so I consider that a gray area. see para (b) https://www.law.cornell.edu/uscode/text/8/1185
Question 1. Can I use this non US passport to exit the country? Does the airline even care I as a US citizen am not using a passport to travel as long as the destinations are valid for entry with this non-US passport? This passport has no US visa on it to allow me to enter. Therefore, I cannot enter or reside in the US with this passport.
The first leg of my trip includes a 1 day layover in Japan which I plant to exit the airport and walk around tokyo. My non-US passport will allow me into Japan visa free.
The next leg is from Japan to Vietnam. Vietnam requires a visa authorization letter (from both my passports) and then they will issue a visa on arrival (which takes up an entire page on my passport plus half a page for entry/exit stamps). My intent is to obtain a visa authorization and arrival on this non-US passport.
Question 2: When I check to my flight leaving the US. Can I just show my non-US passport with the visa authorization for vietnam? Or will I will I be rejected as I don't have an authorization for my US passport?
Alternatively, I was thinking of getting visa authorization letter for both passports. They are cheap. I can just show US passport at check in with visa authorization. This will clear the airline to let me board. when I arrive in Japan I can whip out my non US passport. When I arrive in Vietnam I can whip out my non-US passport with the visa authorization letter. this way I have avoided losing 2-3 pages in my US passport.
The next leg is to the country of my non-US passport. This is inconsequential to my issues.
The final leg is back to the US and I will enter using US passport. No stamps on entry.