The US Federal Aviation Administration (FAA) gives Boeing until 31 December to show that a redesigned component in the ram air turbine of the 787-9 meets airworthiness guidelines, the agency says in a new filing.
Boeing is redesigning the generator control unit in the ram air turbine after one device failed to produce electrical power on one recent flight test and on three subsequent tests on the ground.
Although the ram air turbine was deemed non-compliant with airworthiness regulations, the FAA approved a time-limited exemption as it awarded a type certificate for the 787-9 on 13 June.
Boeing must prove that the redesign meets airworthiness criteria and submit the test data to the FAA by 31 December, the agency says in an 8-page filed dated 12 June, which was posted in the Department of Transportation’s online docket eight days later.
In the meantime, Boeing showed that the odds are “extremely improbable” that the current design defect in the ram air turbine will reduce the safety of the 787-9.
The ram air turbine provides back-up power for the flight controls and avionics if both engines on the 787-9 shut down, but it is rarely needed. Modern aircraft engines rarely fail, and a dual engine shutdown is even more rare. The onboard battery can fully power the flight controls and avionics for 10min, allowing the flightcrew time to activate the auxiliary power unit to take over the load, the FAA filing says.
The ram air turbine is only necessary if the engines cannot be started and the APU fails to activate within 10min.
The odds of a dual engine failure, APU failure and a ram air turbine failure are highly remote, the FAA concludes.
Boeing now six months to prove that the redesigned generator control unit will reliably produce electrical power if needed, as required by airworthiness regulations.
The time-limited exemption for the existing design of the ram air turbine expires at the end of February, the FAA says.
The agency also approved a similar time-limited exemption for an overly sensitive altitude select knob on the mode control panel, giving Boeing until the end of March to submit data showing the redesign functions properly.
Both exemptions allow Boeing to deliver the 787-9 to launch customer Air New Zealand at the end of June.