Qantas this week expects to hear from Rolls-Royce on how it can fully restore its trans-Pacific A380 flights connecting Los Angeles with Melbourne and Sydney.
When Rolls-Royce, the manufacturer of the Trent 900 engine that experienced the 4 November uncontained failure on a Qantas A380, advised Qantas it could resume flights, the caveat was Qantas had to use a lower thrust setting than the maximum 72,000 lbs its Trent 972-84 variant permits. The only other current Trent 900 operators, Lufthansa and Singapore Airlines, use the Trent 970-84 with a maximum of 70,000 lbs of thrust.
The thrust constraints meant an A380 departing Los Angeles could, depending on the runway in use, carry a payload of 20,000 or 30,000 kg. That corresponds to Qantas only being able to fly 80 passengers between America and Australia, an “uncommercial” proposition, the carrier says in Federal Court documents as part of the carrier’s legal claim against Rolls-Royce.
The 20,000 or 30,000 kg payload is 22-34% of the A380′s typical maximum payload of 89,200 kg. It should be noted that after taking the most restricted payload (20,000 kg) and accounting for a generous average of 120 kg per person including luggage and catering provisions, the A380 could carry 166 people, so it seems Qantas is including some freight in its calculations, but the constraints are still severe.
It’s understood the likely concern of using the maximum 72,000 lb thrust setting is that there could be resonating vibrations that cause oil pipes to crack, thus leaking oil and setting the scene for a fire and uncontained engine failure. For the record, CASA says it has no concerns of the A380 operating across the Pacific with limited diversion points compared to mainly overland Kangaroo route to London.
What is not clear is if the resonating vibrations still fit with the current Trent 900 situation.
On 2 December the Australian Transport Safety Bureau said an axial misaligned stub pipe counter-boring, likely occurring during manufacturing, was the probable cause of the QF32 accident, a view upheld the next day in the ATSB’s preliminary report. Stub pipe inspections found the problem replicated on three engines, including two not from Qantas and thus not exposed to the 72,000 lb thrust level. Count out here the resonating vibrations.
Qantas identified 16 Trent 900 engines that needed modification or replacement for a second fault, unrelated to the stub pipe issue: the bearing compartment module producing oil sediments in the high pressure/intermediate pressure chamber. This fault, which is keeping the engines grounded, was not mentioned in the ATSB’s preliminary report, so details are still scant on the cause and if the resonating vibrations had an effect.
The big question hanging over the Trent 900 is if two older variants of the engine, “A mod” and “B mod”, are at fault while the “C mod” operates normally.
Qantas says it only has “A mod” and “B mod” Trent 900s, so it remains to be seen if the solution to restoring trans-Pacific flights is to use “C mod” engines (which with a lack of spares is easier said than done) or if there is a more systemic problem with the Trent 900.
Airlines and others are blaming faulty “A mod” and “B mod” variants for both the stub pipe and the bearing compartment module. Meanwhile Rolls-Royce dithers.