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

Specific details of what will be tested during the flights remain vague. They 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 to help investigators assess the causes of the recent issues, as well as to help in the design of a modified system which will clear the fleet to fly again.

Boeing says the flight test activity will allow it “to conduct testing of the in-flight performance of the airplane’s batteries, which will provide data to support the continuing investigations into the cause of the recent 787 battery incidents.” The FAA amplifies this by saying “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 imposed on Boeing when it conducted a 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 the provisos 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, and will include only personnel essential to the flight.

Boeing will use ZA005, one of the original test fleet, to conduct the flights. This is one of two remaining fully instrumented test aircraft and, until the grounding, was focused on evaluating the improved Performance Improvement Package (PIP) II upgrade version of the General Electric GEnx-1B. ZA005 was the first 787 to be powered by the GEnx-1B, and also recently undertook other pre-certification test work for the upcoming 787-9, including engine windmill re-light tests in November.

The PIP II engine will be the delivery standard for all GEnx-1B powered 787s from late 2013. Rated at up to 78,000 lb thrust, compared to 75,000 lb for the PIP I which was certificated in June 2012, the engine is also designed to cover the power needs of the double-stretch 787-10X.

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