I am 4 weeks pregnant and had a blackout episode today likely due to low blood pressure.

Firstly congratulations.. Air travel is safe. Just keep yourself well hydrated with juice, water, ORS and eat in regular intervals. Keep energy bars in your bag to avoid low blood pressure

congratulations mummy on your pregnancy! please take care and bed rest if you are unwell. as for air travel do check in with your gynae for better advice.