Boeing needs a last-minute regulatory intervention to avoid a delay of the entry-into-service date later this month for the 787-9.
The company has asked the US Federal Aviation Administration (FAA) to quickly approve exemptions that would allow the 787-9 to be delivered on schedule despite two critical flight systems deemed non-compliant with airworthiness regulations.
“The certification process provides a method for identifying component issues that do not result in an immediate safety concern but need to be addressed,” Boeing tells Flightglobal. “We have followed that process and proposed plans to the FAA to address two components on the 787-9.”
The requested exemptions would cover a newly-discovered reliability problem with the ram air turbine (RAT) and a functional issue with the altitude-select dial on the mode control panel, according to a Boeing petition for relief filed on 4 June.
The FAA will have to move quickly to meet Boeing’s timeline. Boeing notes in the filing that 787-9 deliveries should begin in “June 2014”, and any delay processing the exemption will postpone the entry-into-service milestone.
Boeing asks the FAA in the petition to waive a required “publication and comment period” and approve the exemptions.
The RAT – essentially a small windmill – is stowed within the belly of the fuselage and serves as the last line of defence in the event of a rare dual-engine failure.
If both engines shut down in flight, the RAT deploys into the airstream slightly aft of the wingbox to generate enough electrical power to power the flight controls and the avionics. Although the RAT does not provide forward thrust, it should keep the aircraft in controlled flight until the engines restart or the aircraft glides, if possible, to a runway to land.
The RAT on the 787-9 worked properly during a year-long certification campaign. However, a capacitor inside the generator control unit failed during a non-certification flight test, Boeing says in the filing.
An internal review found that the capacitor is unreliable and must be redesigned to meet airworthiness criteria, which require that such a system performs reliably.
The redesign will not be completed, inserted into production and made available for retrofit until February, Boeing says.
Although the existing RAT could fail if deployed, Boeing argues in the filing that the chances of having both engines and the RAT all fail at the same time are “extremely improbable” among the small number of aircraft that enter service before next February.
Boeing also argues in the filing that approving the exemptions is in the public interest because the 787-9s will replace aircraft that are less fuel efficient. The public interest also is served by the positive economic impact of keeping the entry into service date on schedule, Boeing says in the filing.
Boeing also plans to deliver the first batch of 787-9s despite a known problem with the altitude-select dial on the mode control panel.
In vertical navigation mode, the flightcrew sets the altitude by pressing and then rotating the dial. However, Boeing discovered that the dial lacks sufficient torque resistance, so a pilot can inadvertently rotate the dial “by one or two detents” by simply pressing it, according to the filing.
It is possible the crew may realise the mistake before violating the altitude range directed by air traffic control, but “the limited time to detect the error causes a large reduction in safety margins”, Boeing says in the filing.
Boeing is rolling out a revised mode control panel that fixes the problem next May, but needs an exemption from the regulations to allow the 787-9 to enter service on schedule in June.
The FAA did not immediately return phone calls seeking comment about Boeing’s request for exemptions.
Source: Cirium Dashboard
