jsloan

The Air Passenger Duty is applicable only to outbound flights. Someone looking to avoid it should consider returning from an airport in Ireland, Northern Ireland, or continental Europe.

Flexibility is key. As a GS, you're going to have options that most passengers don't, including the ability to upgrade award tickets and the ability to create award inventory. For example, for a roundtrip from Tuesday, April 9 through Thursday, April 18, there is PN9 / XN9 on one of the two daily SFO-LHR flights each day. PN is the booking class for GS upgrades, and XN is the booking class for economy award tickets for elites, including GS. You can see this booking class information by activating Expert Mode (there's a board thread on this). Note that if you're willing to risk sitting in coach for part of the way (e.g., SEA to SFO), you should search just the long-haul segments, since Expert Mode will only show you inventory that's available across the entire journey.

With "only" 10 GPUs, your cheapest path to getting six tickets would be five economy award tickets, supported with GPUs, plus one cash ticket upgraded with miles (yours). Each companion ticket would cost 60K miles RT plus 2 GPUs, taxes, and fees; your ticket would be a $720 base fare, $1100 in upgrade co-pays, and 40K miles total. Waiting until you earn two more GPUs would save $1800 at the cost of an extra 20K miles -- definitely worth it if that's feasible. You could book all of this today on those days -- no waitlisting needed. And those aren't cherry-picked dates; they're literally the first two I came up with. Weekdays are easier to upgrade than weekends.

Note that GPUs expire on January 31st, the second year after they're earned. In other words, if any of these GPUs are from calendar year 2017 spending, they'll expire on January 31, 2019. GPUs earned from 2018 spending will expire on January 31, 2020.