Below is the best I could find. You technically would need to find the likeliest route using today's flight plans and estimate what is interntional waters and work from there - yes a nightmare.
Anyway see below, good luck I feel your pain.
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"Foreign Earned Income and International waters
Earned income is wages, salaries, professional fees, and other amounts received as compensation for personal services. To qualify for the foreign earned income exclusion, the income must be earned in a foreign country. The place where the services are performed determines whether the income is foreign, not the location of the employer or place of payment. For example, if you are a U.S. citizen flight crew member, living and working abroad, receiving wages for services performed in China, those wages qualify as foreign earned income even if you are working for a U.S. airline who deposits your paycheck in a U.S. bank account. As mentioned above, the term "foreign country" includes its airspace and territorial waters, but does not include airspace over international waters, the United States, U.S. territories, or Antarctica. As a result, income earned for performing services as a flight crew member may need to be apportioned to the actual time spent performing services in a foreign country in order to properly determine the amount of foreign earned income.
If you are a flight crew member performing services on international flights, your earned income will need to be apportioned between the:
Income earned in a foreign country (or countries), including the country's airspace and territorial waters, and Income earned in other than a foreign country.
Only the portion of income earned for services provided in or over a foreign country is eligible for the foreign earned income exclusion.
Example: A U.S. citizen flight crew member based at an airport in France mostly works roundtrip flights from France to the United States. When working these roundtrip flights, the aircraft flight path generally crosses France, Spain, and Portugal before crossing international waters and entering U.S. airspace. Income earned for providing services in France prior to departure and while flying in French, Spanish and Portuguese airspace is foreign earned income. Income earned for services provided while the aircraft is flying over international waters, in U.S. airspace, and on the ground in the United States is not foreign earned income.
Computing the Amount of Foreign Earned Income
A flight crew member's earned income is based, in large part, on the services performed from the time the aircraft starts moving away from the gate for departure ("block out" time) until the time the aircraft stops at the gate upon arrival ("block "
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