PAUL LEWIS / MIRABEL CUTAWAY / TIM HALL
Bombardier's new CRJ900 regional jet is evidence that a robust design can be taken a long way even if it is based on a 25-year-old business aircraft
The new CRJ900 represents a bargain development for Bombardier. It provides the Canadian manufacturer with a cost-efficient platform to offer in an emerging market for large regional jets in return for a relatively minimal investment. With 86-90 seats, the aircraft is the ultimate stretch of what has proven to be a robust design with origins that can be traced to the Canadair CL-600 Challenger business aircraft of 25 years ago.
Bombardier's success in developing the design, starting with the launch of the 50-seat CRJ100 in 1989, followed by the 70-seat CRJ700 in early 1997 and the CRJ900 three years ago, owes more to clever engineering and good fortune than any preconceived strategy to develop a 40- to 90-seat family of regional jets. "We always designed for growth capability, but if the question is 'did we design the CRJ700 platform to be capable of going to 90 seats?' then I would say no," says Jean-Guy Blondin, Bombardier CRJ700/900 programme director.
When Bombardier started thinking about a 70-seater, the CRJ100 had only been in service for two years and the focus was on a simple stretch using the same wing. At the end of three years of study, it was decided an all-new wing was needed if the CRJ700 was to meet performance requirements. Development of the 70-seater not only entailed a larger 23.2m (76ft)-span wing, but a redesigned fuselage, new powerplant and major subsystems. With upper limits of US airline scope clause agreements with mainline pilots pegged at 70 seats, no thought was given at the time to going any larger.
Bombardier's product planners instead had been looking at the all-new BRJ-X, but with a five-abreast 90- to 120-seat cabin it was clearly aimed at the lower end of mainline flying rather than traditional regional operators. Market uncertainty, a reluctance to move into an area dominated by Airbus and Boeing and a projected $1.2 billion development bill resulted in the project being shelved in 2000. With Embraer and Fairchild Dornier pushing ahead with 70- to 110-seat clean sheet designs, Bombardier decided to leverage its investment in the CRJ700 and respond with a derivative aimed firmly at its regional clientele.
The lower cost stretch approach was not without its drawbacks, however. The CRJ900 retains the same 70.61m2 (760ft2) wing as its smaller sibling, which Bombardier concedes is not an ideal solution, capping the size of the jet. Compared to the CRJ100/200, the CRJ900 has the same enlarged cabin volume as the CRJ700, but at 2.55m wide it still has a narrower cross-section than the rival four-abreast Embraer 170.
"The CRJ700 was optimised as a 70- to 78-seater. What we did was push the envelope and ended up with an 86-seat aircraft. The CRJ900 is an extremely efficient aircraft that has pushed the design to the maximum capability. If we had been designing a 90- to 96-seater, we would have designed some things differently and changed the wing sizing," says Blondin.
In a single-class, high-density configuration the CRJ900 will accommodate 90 seats at a (78.7cm) 31in pitch, but this is with a single galley, two lavatories, the aft service door inoperative and the rear baggage bulkhead pushed back, compressing the hold to 9.35m3 (330ft3). North American and European carriers are more likely to opt for an 86-seat layout and a full 12.38m3 aft baggage hold. Launch customer Mesa Air, which will be operating the aircraft under the banner of America West Express, has opted for a two-class six/74-seat layout thanks to the addition of a third seat rail permitting a two plus one business seating arrangement.
Structural difference
The principal structural difference from the CRJ700 is the addition of two fuselage plugs, measuring 2.29m forward of the wing and 1.57m aft, increasing the overall nose to tail length to 36.4m compared to the original 20m-long Challenger. The plugs are now an integral part of the mid-fuselage body, produced by Bombardier's Shorts division in Belfast. The only aircraft that used plugs was the lead test aircraft 10001, which was a modified CRJ700.
To meet the 90s cabin evacuation certification requirement under FAR 25, a second pair of Type III overwing emergency exits were added to handle the additional passengers. This in turn has forced the relocation of the fuel vent installation. The optional aft service door, which was added to provide a faster ground turn time, can also be used for evacuation. Unlike the forward Type I main passenger and service doors however, the aft door sill is more than 1.83m off the ground and requires an inflation slide, but "at this point we don't have a customer", says Pierre Alegre, CRJ700/900 in-service manager.
The extended forward fuselage has allowed for a larger, 4.4m3 underfloor baggage hold, an increase of about 30% over the CRJ700. A second 1.07 x 0.51m cargo hold door from Latecoere has been added and, for easier access inside the 0.56m high bay, the aircraft retains the option of a baggage retrieval system introduced on the 70-seater. The two sliding composite trays add about 45kg (100lb), but have proven popular with carriers, with Delta Connection operators Atlantic Southeast Airlines and Comair retroactively deciding to fit the system to their fleet.
While the overall wing dimensions remain constant, the CRJ900's has been strengthened through resizing of the front and rear spars, and wing planks and material changes in the area of the wing fuselage attachments. This has added only about 30kg, which is causing Bombardier to consider standardising on the wing for both the CRJ700 and 900 to reduce build times. The Mitsubishi Heavy Industries-built aft fuselage has also been reinforced to accommodate a sturdier tail strike shock absorber and two ventral fins, added to improve longitudinal stability.
There has been no change to the Goodrich-built nose landing gear other than the introduction of a new tyre with a modified chine for higher speeds. The main landing gear has been strengthened to support the CRJ900's higher operating weights, with the addition of a fifth steel brake rotor and a thicker gauge leg. "What Goodrich did was to remove less material. Externally it's the same and uses the same casting," says Alegre. Standardising gear between the two aircraft is another area being looked at to further maximise commonality and reduce spares costs.
A major CRJ900 selling point for existing operators of the smaller CRJ100/200/700 is the common type rating/common crew qualification across the range of regional jets allowing for mixed fleet flying and reduced training costs. Differences training between the 70- and 86-seater jets amounts to just 4h of ground school, while pilots moving up from the 50-seater would require additional time in a simulator. For a carrier operating 10 CRJs of each variant, Bombardier claims savings in aircrew training, pooling and scheduling alone equate to nearly $50 million over 15 years.
There has been some consideration about updating the CRJ's Rockwell Collins ProLine 4-based cockpit with larger liquid crystal displays in place of the current array of six 150 x 180mm CRTs. While there is not yet a clear-cut business case to make the change, future precision and area navigation requirements may dictate more information be displayed than can currently be accommodated on the electronic flight instruments. Nearer-term additions being made to the CRJ700/900 include Mode S transponder, VHF datalink and, downstream from this, controller pilot datalink communications.
Auxiliary power
Electrical and hydraulic power is 100% common, as is the tailcone-mounted Honeywell RE-220 auxiliary power unit, which is designed to start in flight up to an altitude of 37,000ft (11,300m) and operate to the full 41,000ft ceiling. The aircraft's environmental control system remains essentially the same, bar some software logic and valve modifications. "Early in the CRJ700 programme we were having problems with the temperature pull-down requirements and we fixed it so aggressively that there is only a few minutes' difference with the CRJ900," says Blondin.
The major system change centres on the switch to the uprated 14,500lb-thrust (54.5kN) General Electric CF34-8C5 turbofan engine, which offers 5% more power than the 70-seater's -8C1 powerplant. Changes are focused on allowing the engine to run hotter without a resulting loss of material durability. Accordingly, there are improved cooling flows to the low-pressure turbine (LPT) and high-pressure turbine modules and material changes to the combuster and LPT blades. Early CRJ900s are fitted with a chevron nozzle, but Bombardier has decided to revert to a straight design, which the company is confident of meeting Stage 4 noise requirements and a promise from GE of improved specific fuel consumption.
There is an option for a further 2% increase in thrust to improve the aircraft's take-off performance. The CRJ900's longer fuselage limits its angle of attack on take-off compared to the CRJ700 and this typically translates into a 300m longer take-off run. As an alternative to a throttle push, which has a knock-on impact on temperature and durability, Bombardier has developed an overspeed chart for the CRJ900 to accelerate the aircraft to a higher take-off speed before rotation. Payload/range performance is particularly critical out of hot and high airports such as Mesa home port of Phoenix, Arizona.
Bombardier is offering airlines three different weight options to optimise landing fees, ranging from a baseline CRJ900 maximum take-off weight (MTOW) of 36,514kg up to the CRJ900LR at 38,330kg. Mesa has opted for the CRJ900ER version with a MTOW of 37,421kg and a range of 3,156km (1,706nm), compared to the CRJ700ER's 3,672km range carrying 16 fewer passengers. Operating from Cincinatti, Ohio, this puts southern California, western Canada or Central America all within range.
The CRJ700 and 900 share a common production line at Bombardier's new purpose-built facility at Mirabel, north of Montreal. Jigs and tooling have been designed to accommodate either size aircraft to maximise manufacturing flexibility. Production is heavily weighted five to one in favour of the CRJ700, with the first CRJ900 having been delivered in February to Mesa. Orders to date total 25 aircraft for Mesa and 10 for GE Capital Aviation Service, with options on 40 aircraft.
Bombardier hopes the CRJ900's introduction to airline service will be without the difficulties encountered by the CRJ700 over the past two years. The company is building on that experience and the post-production modification package now in place for the 70-seater. Bombardier is halfway through its engine indication and crew alerting system (EICAS) V5 programme of upgrades and has taken advantage of the two-week downtime on each aircraft to make other reliability and small structural modification.
Nuisance messages
EICAS V5 includes a series of software modifications to eliminate problems such as nuisance messages. It also entails the replacement of selected avionics line replaceable units and rotable hardware, like the main landing gear retraction actuator, which is being fitted with a pressure switch to detect valve failure. Other rework examples include adjusting threshold measurements on the wing to avoid triggering false ice caution messages. Changes are also being made to provide more flexible fuel and hydraulic lines to avoid leaks.
"The CRJ900 will be going into themarket with the latest configuration and we think will probably have better reliability out of the box than the CRJ700. We're very happy with the level of modifications and status of the aircraft delivered," says Blondin, who adds a note of caution: "It is only when you launch the aircraft into service do you really find out what the issues are."
Source: Flight International
