xliioper

There is a difference between D1 marketed flights and simply having D1 equipment (there are a number of routes out of DTW/ATL in May that have D1 equipment, but are FC marketed because they are not D1 routes). While JFK-SEA has D1 marketed flights on the route, sometimes they will have D1 equipment that is not D1 marketed. I did a test booking and the companion cert was accepting for at least some of these FC marketed flights. There's a built-in fare surcharge in domestic FC fares of $100 - $150 each way for flights including D1 equipment (the neo's get the $150 surcharge).

Looking at the fare rules for the D1 fares on this route, the issue here appears they have not updated the fare rules yet to include A330-900neo flights. Since it falls outside the scope of the D1 fares, it's booked as a regular FC fare. Presumably, they will update the equipment list in the D1 fare rules to include it at some point.

THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON AIRBUS INDUSTRIE A330-200
ON NONSTOP FLIGHTS.
AND
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
ANY DL FLIGHT.
THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON AIRBUS INDUSTRIE 330-300
ON NONSTOP FLIGHTS.
AND
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
ANY DL FLIGHT.
THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON AIRBUS A359
ON NONSTOP FLIGHTS.
AND
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
ANY DL FLIGHT.
THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON BOEING 757 200 WINGLETS
ON NONSTOP FLIGHTS.
AND
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
ANY DL FLIGHT.
THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON BOEING 767-400
ON NONSTOP FLIGHTS.
AND
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
ANY DL FLIGHT.
THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON BOEING 767-300
ON NONSTOP FLIGHTS.
AND
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
ANY DL FLIGHT.
THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON BOEING 777
ON NONSTOP FLIGHTS.
AND
THE FARE COMPONENT MUST BE ON
ONE OR MORE OF THE FOLLOWING
ANY DL FLIGHT.
THE FARE COMPONENT MUST INCLUDE TRAVEL BETWEEN JFK
AIRPORT AND SAN/SEA
ON BOEING 777-200LR
ON NONSTOP FLIGHTS.