In-flight cosmic radiation doses along the current alternative routes between Tokyo and Frankfurt

Calculation-based dose assessment for aircraft crew is required worldwide by authorities, as cosmic radiation dose rates at aviation altitudes are substantially higher than at sea level. The accuracy of the calculated in-flight dose onboard aircraft ("route dose" hereafter) should be confirmed periodically, particularly when the flight route is significantly changed.

We focused on the long-haul flights between Tokyo and Frankfurt, which have recently undergone significant changes owing to the geopolitical conflicts between Ukraine and the Russian Federation and in the Middle East. The route doses for a round trip in February 2026 under solar maximum conditions were calculated using actual flight path records and the JISCARD EX route-dose calculation program. Calculated route doses were compared with measurements obtained using an electronic neutron dosimeter to check the consistency.

The in-flight effective doses were estimated to be 51 μSv for the north route from Tokyo to Frankfurt and 30 μSv for the south route from Frankfurt to Tokyo. In-flight measurements using the electronic neutron dosimeter showed trends consistent with calculated ambient dose equivalents of heavy charged particles. The effective doses for the north and south routes with a specified constant cruising altitude of 40,000 ft. increased by 10% and decreased by 24%, respectively, compared to the great-circle route doses.

The findings in this study indicate that recent route changes have substantially altered the pattern of cosmic radiation exposure onboard aircraft. While changes in the total in-flight dose may be generally small and annual doses of aircraft crew would decrease if their onboard working hours are carefully managed, the potential risk of elevated radiation exposure due to a solar particle event is higher on the north route.