After four months and more than 1,500 flight hours in service, launch operator Swiss's initial impression of the Bombardier’s CSeries aircraft family is still being formed, but trending in a positive direction.

Until Air Baltic’s first CS300 enters service early next year, Swiss is still the only CSeries operator with a fleet of three CS100s - or about half as many as Swiss had hoped to receive by this time, which, according to Bombardier, is due to a shortage of Pratt & Whitney PW1500 geared turbofan engines. Engine deliveries have been slowed, in turn, by a shortage of critical parts, including the P&W’s hybrid aluminium-titanium fan blades.

The slow pace of aircraft deliveries is, in fact, Swiss’s only source of real disappointment with the CS100, so far, Peter Koch, a Swiss senior director and fleet chief for the CSeries, tells FlightGlobal on the sidelines of the CS300 delivery ceremony to Air Baltic on 28 November.

“All I need is more aircraft and some [fan] blades,” Koch says.

Compared to re-engined and re-winged rivals, Bombardier took on considerably more risk with the clean-sheet CSeries, a decision that exposed to the company to a costly 2.5-year delay during flight test. Despite early struggles with mastering the CSeries’ pioneering fly-by-wire architecture, the aircraft has transitioned from flight test to revenue service with fewer of the “teething” issues that plagued the reliability of other aircraft types, such as the Boeing 787-8.

“The aircraft is actually behaving much better at entry into service that we expected,” Koch says.

As a subsidiary of Lufthansa, an airline highly experienced with introducing new aircraft types, Swiss’s expectations for the CS100’s debut were set slightly lower than Bombardier’s pronounced goal of achieving a “flawless” entry into service. Bombardier defined flawless as a dispatch rate of at least 99%, a standard that would compare the upstart CSeries favourably with far more mature competitors in the narrowbody sector.

With only three CS100s flying, Koch cautions against drawing too many conclusions from such a statistically small sample. Weekly trends shift more dramatically with a fleet of three than of 20, which is Swiss’s planned stable of CS100s within two years. So far, the three-member CS100 fleet runs below the 99% dispatch reliability standard on some weeks, he says.

But the overall trend still exceeds Swiss’s expectations. Software bugs are a frequent source of serious teething problems for new aircraft, especially those featuring advanced fly-by-wire control systems. The main irritation are “nuisance messages”, which distract the flight crew with unnecessary status messages or — more worrisomely — phantom caution alerts.

The Rockwell Collins integrated avionics suite is producing nuisance status messages, Koch says, but so far no caution alerts. More encouragingly, any status messages that have appeared have been limited to “two or three” recurring bugs, he adds. On some flights, no such nuisance status message appear at all.

“They are the same messages we had at the beginning, so it’s not like on other [aircraft] types that every week you get another punch with surprise and surprise,” Koch says, adding that Bombardier is working to develop software upgrades to eliminate the nuisance messages.

Pilots are also adapting to the unique procedures and feel of the new aircraft. Swiss has trained more than 90 pilots already, with backgrounds ranging from BAe Avro and Embraer regional jets to the fly-by-wire Airbus A320. For pilots transitioning from the latter, Bombardier’s approach to fly-by-wire is noticeably different.

“The big difference is what we see from fly-by-wire technology from Airbus when the guys want to initiate a turn, they do like this —,” says Koch, miming making sharp lateral movements with his hand into a control stick. The A320 would then begin a gradual turn, whereas for the CSeries the reaction of the flight control computer feels more immediate, he says.

“You steer the aircraft to where you want to go without having to think that a computer is in the middle,” Koch explains.

Swiss is still measuring the CS100’s precise fuel burn data, so has not reached a final conclusion on the central performance issue for Bombardier’s latest commercial product. The initial data, however, seems promising.

“We’re very happy with the fuel burn,” Koch says. “The performance of the aircraft shows to be even better than what Bombardier promised, but now we’re waiting for the statistics.”

In addition to inserting fly-by-wire, Bombardier introduced several new technologies in the CSeries to make the airframe more efficient. The wing skins are made using a liquid infusion technique inside an autoclave that makes the panels lighter than metal. The fuselage itself is made using lightweight aluminium-lithium alloy. But the biggest change was Bombardier’s decision in 2008 to adopt the P&W geared turbofan. By using the gear to disconnect the rotation speeds of the fan and low pressure turbine, P&W was able to widen the fan diameter and double the bypass ratio, a key measure of fuel efficiency.

But there are trade-offs to improving fuel efficiency, and one of those trade-offs appear to be longer start-up times for the engines. Pilots are required to motor such engines for longer than usually required to blow out trapped heat, which would otherwise damage the core, in an effect called rotor bow.

The CSeries is less exposed to the start-up delay than the version of the A320neo powered by a larger PW1100G. Early customers complained of start-up delays measuring several minutes to fire up both engines, when the industry standard is 2min or less. By contrast, the CS100 requires 2min30sec to start-up both engines, Koch says.

“So it’s longer than other engines but still within a good timeframe,” he says.

For P&W, the motor-to-start delay problem is no longer an issue. A series of hardware and software fixes have been installed in the PW1100Gs that shorten the engine start-up sequence.

“Newer generation engines use a motoring sequence to optimize engine performance and the total start time is very similar to the V2500 engine,” P&W tells FlightGlobal . “The issues are now behind us and the engines that we are delivering today have all of the fixes in place.”

But Koch does not seem convinced that the motor-to-start problem is completely in the past, even for the CSeries. Bombardier and Swiss are working on ways to optimise the start sequence, perhaps shaving several seconds from the motor-to-start procedure by starting the second engine near the end of the start procedure for the first engine, Koch says.

It is one of several ideas being developed since the first meeting in October of the CSeries’ Flight Operations Steering Group, which consists of launch operators Swiss and Air Baltic, plus follow-on operators Delta, Air Canada and Korean, Koch says.

“So now the exchange is starting,” he adds, “which I like because we’re not the only ones.”

Source: Cirium Dashboard