What exactly does "Commander" mean? Synonym of First Officer? I know that in the navies of the Commonwealth and US, three full stripes (like those worn by FOs) denote Commander, 4 Captain. &quot;Because Pan Am operated flying boats, the company decided to step away from the WWI military pilot look and dress its line pilots in an outfit closely resembling naval officer uniforms.&quot;
Why exactly does Cathay Pacific call their Relief Pilots Commanders? Do any other airlines do this? Does Commander merely synonymize Senior First Officer?

From there you will move on to become a Junior First Officer, First Officer, Senior First Officer (Relief commander) and then onto becoming a Captain.

A Day in the Life of a 747 Pilot - Cargo Clan

Two crew – one of whom must be a relief commander or another Captain – occupy the flying seats while other crew rest, usually splitting the rest period equally.

I screenshot some CX pilots' Linkedin profiles. Nick Papas.

Richard Stroud

Justin Wills.

Frankie Wong.

You can hear &quot;Relief Commander&quot; blazoned at 5:35, but Capt. Anthony Peterso?e?n's voice is too muffled. The first Relief Commander is Thomas TaTower? Second Relief CDR is Steve ZaHower?
I know nothing about Cathay Pacific ranks/titles, but the plain words seem pretty logical.
The Captain, as Pilot In Command, is legally responsible for the entire flight. But who is actually in command while the Captain is required to be resting on long flights?
You don’t want the two most senior pilots resting at the same time; it would be unsafe to put a junior pilot in command for half the flight. So, you designate the second most senior pilot, who is still technically a First Officer, to be in command while the Captain is resting.