If I fly from London at 11.30AM and reach Los Angeles at 4PM do I have to offer any prayers on the flight? And if on return I leave LA at 7.30PM and arrive in London at 3.00PM the next day, do I have to offer all 5 prayers on the flight?
Salaam alaykum, you can pray your dhuhr salah before maghrib once you arrive in LA. You need to pray maghrib-'isha, and fajr on the flight back to London. If you can pray dhuhr-'asr before maghrib in London, then you can do that, as maghrib is now approx 6:00 pm.