As I understand it, BX1Bs come out of same U or Z inventory as regular biz class or first plan aahead awards.

here's what the BE webpage says for this award:
BX1B PlanAAheadŽ Award - Continental U.S., Canada and Mexico (Business / First 2 class cabin flights)
Award Code:

BX1B
Point Value:

3200
Description

Continental U.S. (including Alaska), Canada and Mexico
Terms and Conditions

PlanAAhead Award Travel within and between the Continental U.S. (including Alaska*), Canada and Mexico in First Class/Business Class**

*American Airlines service to Alaska is seasonal.
**Valid for First Class on flights with two-cabin service and for Business Class on flights with three-cabin service.
Valid to/from Mexico or Canada for Business Class.

PlanAAhead Awards are valid for one-way or round-trip travel, are subject to special limitations on seat availability and may be subject to travel embargo dates.

Once redeemed via BusinessExtra.com, a confirmation email with the Electronic Authorization Number is sent to the Travel Manager. The Electronic Authorization includes the Award Code along with an eight character alpha-numeric code. (IE. BX1A/0A1B2C3D) This number should be provided to American Airlines Reservations when you are ready to ticket your award reservation.

To make reservations for award travel: Calling from within United States or Canada, please contact American Airlines Meeting Services at 1-800-433-1790, 7 days a week, from 6:00AM to 12:00midnight, CT. If calling from outside the U.S. or Canada, please contact your local American Airlines Reservations Office.

All travel awards must be ticketed 5 days after the reservation is made or 14 days prior to departure whichever date comes first. If the reservation is made less than 14 days prior to departure, the reservation can be held for 48 hours for ticketing. All ticketing must be done through AA reservations prior to arrival at the airport. Airport agents are unable to issue tickets against Business Extra awards.

Award ticket must be issued by midnight one year from the original award redemption date. Tickets issued against Business Extra flight awards are then valid for one year from the ticket issue date.

Award tickets are non-transferable and a non-refundable change fee will apply to reservation changes after the ticket is issued.

All taxes and fees, assessed at the time of ticketing are the responsibility of the passenger. Award cannot be used in conjunction with any corporate program, promotion, coupon, discount, or special offer of American. Void where prohibited by law.

Award travel valid ONLY on American Airlines, American EagleŽ, US Airways and US Airways Express℠ flights.

Award is not redeemable for cash and is void if sold for cash or other consideration.

A ticket issued against this award is nontransferable. Open tickets may not be issued.

Awards are valid only for tickets issued on American Airlines ticket stock. Award is not applicable to the purchase of a Miscellaneous Charge Order (MCO) or Prepaid Ticket (PTA).

Award has no value except when redeemed in accordance with these terms and conditions.

Travel is valid as specified above to American Airlines, American Eagle, US Airways and US Airways Express destinations served both at the time of award redemption and ticket usage.

Rules as written herein cannot be changed by any statement or representation of any unauthorized person, including employees of American Airlines or issuing organization.
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