Boeing has received the go-ahead from the FAA to conduct data-gathering test flights of the 787 as part of the ongoing investigation into the causes of two battery failures that have grounded the fleet since Jan 16.

Although Boeing has not yet specified the details of what will be tested during the flights, these are thought to be aimed at measuring the environmental conditions in and around the batteries which are located in the forward and aft electrical/electronics bays. Boeing wants to characterize the temperature, humidity and vibration levels in the battery and the related electrical system, to help investigators assess the root cause of the recent issues, as well as to help in the design of a modified system which will clear the fleet to fly again.

The FAA says “the primary purpose of the test flights will be to collect data about the battery and electrical system performance while the aircraft is airborne.” The agency adds that the flights will be conducted in defined airspace over unpopulated areas, and will be subject to a “number of restrictions, including extensive pre-flight testing and inspections and in-flight monitoring in order to ensure the highest levels of safety.”

Echoing some of the provisos levied on Boeing when it conducted the Feb 7 ferry flight of a 787 from Texas back to Everett, Wash, the FAA granted Boeing a “Special Airworthiness Certificate (for the purpose of Research and Development)” to conduct the test flights. In particular these include the requirement that before flight, the crew must perform “a number of inspections to verify that the batteries and cables show no signs of damage.” The FAA says the pre-flight checklist will also include a mandatory check for specific status messages that could indicate possible battery problems.

Once airborne, the agency says the crew “must continuously monitor the flight computer for battery related status messages, and land immediately if one occurs.” Before the initial test flight, the crew must also inspect the airplane’s smoke barriers and insulation to verify that they meet the approved design. It also adds that experimental research and development flights will only be flown with Boeing aircrews that include only personnel essential to the flight.”

It is not yet clear which aircraft Boeing plans to use to conduct the testing, or whether multiple aircraft will be covered by the certificate. Likely candidates include dedicated test aircraft ZA004 and ZA005, both of which are thought to be instrumented in readiness for engine upgrade and other flight tests linked to fleet improvements and the upcoming 787-9 certification program.

In addition to the FAA’s root cause analysis, the FAA says it is continuing to conduct a comprehensive review of the 787’s critical systems, including the aircraft’s design, manufacture and assembly.