an Bord
on board
To be in a vehicle, especially on an airplane, ship, or train.
Willkommen an Bord dieses Fluges nach Lissabon.
Welcome aboard this flight to Lisbon.

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on board
To be in a vehicle, especially on an airplane, ship, or train.
Willkommen an Bord dieses Fluges nach Lissabon.
Welcome aboard this flight to Lisbon.

The noun 'Bord' is used almost exclusively in fixed expressions with prepositions. It is rarely used on its own with an article like 'das Bord'.
Alle Passagiere müssen jetzt an Bord kommen.
All passengers must now come on board.
The preposition indicates the direction: 'an Bord' (to be on the vehicle or to get onto it), 'von Bord' (to leave the vehicle), and 'über Bord' (from the vehicle into the water).
Die Crew ist schon an Bord des Schiffes.
The crew is already on board the ship.
The phrase 'etwas über Bord werfen' (to throw something overboard) is often used figuratively. It then means to give up or discard a plan, an idea, or principles.
Wegen der neuen Situation mussten wir unsere alten Pläne über Bord werfen.
Because of the new situation, we had to throw our old plans overboard.
to leave / rely
'verlassen' and 'von Bord gehen' can both mean that you leave a means of transport. 'verlassen' is more general: you can leave a house, a room, a city, a group, or also a ship. 'von Bord gehen' belongs to 'das Bord' and is especially used with ships, airplanes, or similar means of transport. It sounds more precise when you want to emphasize that someone is no longer on board. In everyday language, people often simply say 'das Flugzeug verlassen' (to leave the airplane), but with ships, 'von Bord gehen' (to disembark) is very natural.

Im Hafen gehen die Reisenden von Bord und holen ihre Koffer.
In the harbor, the travelers disembark and pick up their suitcases.
Nach der Durchsage verlassen die Passagiere langsam das Flugzeug.
After the announcement, the passengers slowly leave the airplane.