Boeing test pilots have begun simulator sessions at the company’s test and development complex at Boeing Field, near Seattle, in the run-up to certification ground and flight tests of the modified 787 battery system.

The pilot rehearsal gets under way as Boeing continues engineering tests of a revised power panel design on Line No. 86, the aircraft also designated to conduct the upcoming battery certification demonstration flight for the FAA. The power panel testing is designed to tackle in-service issues with the 787’s complex electrical system and is unrelated to the battery modification, says Boeing.

LN86, destined for LOT Polish Airlines, has flown twice since the FAA approved Boeing’s modified battery system certification plan in mid-March. The aircraft, which performed ground and flight tests of the panel on April 3, last flew on April 1. Until now, all the flight testing has been focused on continued functional checks as well as other changes related to improvements in the aircraft’s electrical, systems monitoring and standby instrument displays.

The April 1 flight also is understood to have included tests of the engine anti-ice system, though it is unclear if these were concerned with improvements to the system–which uses engine bleed air–or as part of functional checks of the existing system in preparation for the upcoming battery certification demonstration flight.

The current ground-testing phase continues to focus on the evaluation of the modified battery system and involves heavy use of the 787 Integration Test Vehicle (ITV), a 75-ton hybrid test rig at Boeing Field. The ITV incorporates flight control and hydraulic systems, linked to test benches of systems software. For ground checks of the battery, the ITV is thought to be interconnected with other nearby laboratories and test facilities that will simulate the electrical loads to be tested in the flight.

Ground tests of the battery will culminate with the deliberate over-charging of a battery and all eight of the unit’s cells simultaneously to demonstrate the ability of the new enclosure to handle a full-blown thermal runaway of the battery. Boeing hopes that, as a result of the upcoming flight and ground testing, the FAA will approve the modifications and allow the 787 to resume commercial flights. The aircraft have been grounded around the world following two battery failures in January.