Here is the receipt e-mailed to me for an upcoming DL trip I have on DL using an "UP" fare:
DELTA CONFIRMATION #: XXXXXX
TICKET #: 006XXXXXXXXXXX
Bkng Meals/ Seat/
Day Date Flight Status Class City Time Other Cabin
--- ----- --------------- ------ ----- ---------------- ------ ------ ------
Sat XXSEP DELTA 7778* OK T LV PHOENIX 405P 8A
AR LOS ANGELES 525P COACH
*Operated by EXPRESSJET AIRLINES
Sun XXSEP DELTA 1255 OK A LV SEATTLE 345P 2C
AR SALT LAKE CITY 644P FIRST
Sun XXSEP DELTA 1832 OK A LV SALT LAKE CITY 918P 1B FIRST
AR PHOENIX 958P
Passenger Information
COpltASgldPHX
Skymiles Number: *******336
Billing Details
Receipt Information
Fare Details: PHX DL LAX45.58T21NBVE/-SEA DL X/SLC DL PHX328.37Q7UPBV USD373.95END ZP PHXSEASLC XT AY 7.50 XF 13.50 PHX4.5SEA4.5SLC4.5
As you can see, booked/ticketed into A/First but the fare calculation for SEA DL X/SLC PHX (which in airline-speak means the portion of the fare from Seattle on Delta connecting thru SLC and ending in Phoenix) shows a base fare of 328.37 and a fare basis code of Q7UPBV. The "UP" part of the fare is why I was booked into A/First but it doesn't change the fact the the fare is a coach Q class fare. The F fare (F0BV) is 683. If there is an equipment change or IRROPS which cause me to be re-accommodated DL is only obligated to give me a coach seat even if they rebook me on another airline from SEA to PHX.