Bad assumption.

Random dates, Jan 18-25, all prices and mileage amounts are roundtrip:

LHR-BOS-LHR
£853.19 total in AA B fare code (Upgrade to business with 30,000 AA miles or 40,000 BA Avios)
£1,055.39 total in BA T fare code (Upgrade to business with 25,000 AA miles or 20,000 BA Avios)

LHR-JFK-LHR
£832.11 total in AA B fare code (Upgrade to business with 30,000 AA miles or 40,000 BA Avios)
£1,033.72 total in BA T fare code (Upgrade to business with 25,000 AA miles or 20,000 BA Avios)

LHR-ORD-LHR
£912.64 total in AA B fare code (Upgrade to business with 30,000 AA miles or 40,000 BA Avios)
£1,067.57 total in BA T fare code (Upgrade to business with 25,000 AA miles or 20,000 BA Avios)

LHR-MIA-LHR
£1,004.86 total in AA B fare code (Upgrade to business with 30,000 AA miles or 50,000 BA Avios)
£1,127.09 total in BA T fare code (Upgrade to business with 25,000 AA miles or 25,000 BA Avios)

LHR-DFW-LHR
£977.09 total in AA B fare code (Upgrade to business with 30,000 AA miles or 50,000 BA Avios)
£1,128.16 total in BA T fare code (Upgrade to business with 25,000 AA miles or 25,000 BA Avios)

LHR-LAX-LHR
£953.362 total in AA B fare code (Upgrade to business with 30,000 AA miles or 50,000 BA Avios)
£1,140.90 total in BA T fare code (Upgrade to business with 25,000 AA miles or 25,000 BA Avios)



AA miles to upgrade BA: http://www.aa.com/i18n/utility/jba-u...servations.jsp

AA miles to upgrade AA: http://www.aa.com/i18n/disclaimers/o...rade-chart.jsp

BA Avios to upgrade: https://www.britishairways.com/trave...club/_gf/en_gb


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Unlike BA, ALL fare classes on AA are upgradeable with AAdvantage miles including the very cheapest ones. However the cheap AA fare classes require 50,000 AA miles + $700 USD co-pay; Buying B class to upgrade with 25,000 miles and no $ co-pay is usually the better deal from the UK market. B class, like WT+ on BA, also earns extra elite qualification points (in both Avios and AAdvantage) making the value even more attractive. From the US market, B class on AA is more money than ex UK, so buying the cheapest ticket and using 50,000 AA miles + $700 USD co-pay is often the lowest $ option.

Unfortunately, I don't know an easy way to ticket AA B class online. AA really should make their website MFU friendly like BA does. ^ I have always called AA to book AA "B class" or used a travel agent.

To check "B class" pricing, one can use ITA software:
- Go to http://matrix.itasoftware.com/
- Click "Advanced routing codes" and enter "/ f bc=b" in each box below the airports.
- Now search and only B class fares will be displaced. Choose AA from the top bar to only see AA B fares.
(To search BA WT+ T fares, enter "/ f bc=t")