I just did a test (composed by a non-native speaker) and in the test, there was the following multiple-choice question:
There were a lot of people _________ the plane.
- aboard of
- on board of
- on board
- on the board of
I chose the answer 4. but according to the test, 3. is the only possible answer. What do the natives speakers of English think? Is really the 4th answer a wrong one?
Please note that I'm not a teacher.