Boeing is cleared to deliver the first 787-9 later in June after being certificated for commercial service by the US Federal Aviation Administration and the European Aviation Safety Agency (EASA).

The award came after the FAA granted temporary exemptions for two components – including the ram air turbine (RAT) – that Boeing deems non-compliant with regulations.

The type certificate for the first stretched variant of the 787-8 caps a four-year development effort, plus nine months and 1,500h of flight testing that began last September.

Boeing expects the 280-seat 787-9 to become the highest-selling member of the 787, with the longest range at 8,300nm (15,400km) and a cabin stretched by 6m (20ft) compared to the 787-8. Twenty-six identified customers have ordered 413 787-9s, accounting for nearly 40% of the 787 backlog.

The first 787-9 is expected to enter service a few hundred kilograms below the specification weight of 251,000kg (553,000lb). It will also be delivered with extended operations (ETOPS) clearance beyond 180min, allowing carriers to fly the twin-engined jet on routes up to 240min or 330min – depending on the volume of halon fire suppressant on board – from the nearest divert runway.

Following on the heels of the troubled introduction of the 787-8, Mark Jenks, Boeing vice-president of 787 development, hails the 787-9 for achieving a “flawless first flight and our on-time certification”.

Boeing acknowledges, however, that two issues arose during flight testing that caused the company to seek time-limited exemptions from the FAA.

In a petition dated on 4 June Boeing asked the FAA to grant the exemptions and to waive a mandatory public comment period, or else the entry-into-service for the 787-9 would be delayed.

In the event of simultaneous failures of both engines and the auxiliary power unit, the RAT deploys to allow the pilot to keep the aircraft stable by providing power to the flight controls and avionics. In a recent flight test, the generator control unit in the RAT failed.

The cause of the failure was traced to a flaw in the assembly process of a generator control unit (GCU) within the RAT, says Bob Whittington, Boeing’s vice-president and chief engineer of the 787 programme.

The GCU consists of a circuit board and a capacitor, each designed to within a range of tolerances. If the board is built at the end of its tolerance range and the capacitor is on the low end, the performance of the capacitor degrades with each use, Whittington says. It can degrade so much that the RAT is unable to generate electricity, because the degraded capacitor prevents the GCU from activating, he says.

“It’s something we need to go fix,” he says.

A new GCU design will be ready to enter production in February, and Boeing will recommend a retrofit for all 787s delivered before that date. The issue applies to the 787-8 and the 787-9.

Although the RAT is a critical safety feature, Boeing has analysed that the risk of a system failure between now and February is “extremely improbable”.

A simultaneous failure of both engines and the APU is very rare, with a design probability of one in 100 million, Whittington says. The odds of such a power loss – followed by a RAT failure – are considered at least one in 100 billion, he says.

“So we asked for a time-limited exemption, which, by the way, is part of the normal process,” Whittington says. “We did this on every single airplane. I don’t know that we’ve ever done a [type certificate] on an airplane without it.”

Ramping up deliveries of the more lucrative 787-9 model is a critical piece of Boeing’s strategy to achieve profitability on the overall programme after a long series of delays and operational setbacks.

Source: Cirium Dashboard