Supplier of oxygen required at first for passenger plane (8)

I believe the answer is:

airliner

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'passenger plane' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

(Other definitions for airliner that I've seen before include "Passenger craft" , "Eg, Jumbo, Concorde" , "Passenger plane" , "Commercial plane" , "Large plane" .)

I've seen this clue in The Times.

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