MIKE GERZANICS / WICHITA

The world's fastest business jet, the upgraded Cessna Citation X, proves itself easy to fly at both ends of its wide speed range

While Boeing struggles to put a price on the value of speed in developing the Sonic Cruiser, Cessna has already found a definitive solution for the business jet market. Around $19 million will buy the fastest civil aircraft available, the Citation X, newly revamped for the 2002 model year.

First flown in 1994, the X traces its bloodline to the hugely successful Citation series, but this aircraft is a different beast. One glance shows that the X, its wing swept 37°, is built for speed. While most Citations have top speeds well under Mach 0.8, the X can reach M0.92. No other business jet can match its M0.9 cruise speed.

This year Cessna introduced its first major upgrade of the X. Highlights include 5% more thrust from the Rolls-Royce AE3007 engines, a 180kg (400lb) increase in maximum take-off weight and enhanced Honeywell avionics. Increased thrust has reduced take-off field length requirements. The higher gross weight allows seven passengers to be carried with full fuel. Top speed remains M0.92, and range is virtually unchanged.

During the pre-flight walk around, senior demonstration pilot Mark Snider pointed out the X's unique features. The cockpit windshield lacks wipers; a special coating and steep rake are sufficient to clear rain. The prominent wing-fuselage fairing reduces drag and allows hydraulic and control lines to be moved outside the pressurised cabin, permitting the seats to be lowered to create more space.

The 49m2 (530ft2) supercritical wing is an impressive piece of engineering: twist varies continuously from root to tip. The trailing edge is directly below the high-mounted engines and the root plunges steeply where it meets the fuselage, to reduce interference drag and preserve area ruling.

A highly polished single-piece leading-edge slat spans the wing's outer two-thirds. The wing, the upper surface of which is exceptionally smooth to promote laminar flow, is also remarkable for what it lacks. Apart from a small leading-edge stall strip, there are no other protuberances such as wing fences or vortex generators.

Oil level in the two AE3007C engines is readily checked from ramp level. A fold-out ladder on the left side gives access to the 2.04m3 (72ft3) heated and pressurised aft-fuselage baggage compartment. There is a 2.11m-long ski tube in the unpressurised fairing.

Largest cabin

Entrance to the cabin is via a counterbalanced door with integral steps. Bleed air is used to inflate both a primary seal and an acoustic seal. The passive secondary seal is configured so that, if there is a loss of bleed air, cabin pressure will maintain the seal.

The cabin, the largest offered by Cessna, is configured for nine passengers with double-club seating and a belted lavatory. A recessed centre aisle runs the length of the 6.77m-long cabin, giving 1.72m of headroom. Sliding pocket doors separate the cabin from the cockpit.

Using the alignment balls on the windshield's centre pillar to find a good seating position, I strapped into the left seat's five-point harness. Field of view from the six-window cockpit was good and I could scan the outer two-thirds of the wing. The rudder pedals have three positions, the centre one giving full throw. The throttles fell comfortably to hand, but the yoke was too high to allow my elbow to sit on the armrest.

The instrument panel is well arranged, with autopilot/flight director switches beneath the glareshield. The Honeywell Primus 2000 electronic flight instrument system has five 200 x 180mm (8 x 7in) CRTs, giving each pilot a primary flight display (PFD) and multifunction display (MFD). The centre tube acts as an engine indicating and crew alerting system display.

Three conventional standby flight instruments are located above the pilot's MFD. An angle-of-attack (AoA) gauge, to the left of the pilot's PFD, is a nice addition to the panel. Systems switches are logically arranged at the panel's lower edge. Control display units (CDUs) for the dual flight management systems (FMSs) are easy to reach at the head of the centre pedestal. A radio management unit (RMU) is placed aft of each CDU.

Cockpit set-up and FMS initialisation were routine. The aircraft has dual GPS and laser inertial reference systems. Alignment took less than 7min. Loading the performance page and choosing between 5¼ or 15¼ flap allowed the FMS to calculate our take-off speeds. These were displayed only on the CDU. Although the aircraft has a standalone take-off warning system, take-off speeds were displayed on the PFDs and MFDs only after flaps had been extended.

The right engine was started first using auxiliary power unit bleed air. Once the start button was depressed, the throttle was immediately brought to the idle position.  The full-authority digital engine control (FADEC) managed ignition and fuel to ensure a safe start. Both engines reached idle RPM about 45s after starter engagement, the inter-turbine temperatures peaking well below the limit of 800¼C (1,473°F).

Idle thrust was enough to start the 13,286kg (29,290lb) aircraft rolling when the parking brake was released. The empty weight of 9,979kg included two pilots, but not the second demonstration pilot in the cabin. Two wing tanks and a centre fuselage tank held 3,230kg of fuel, just over half the maximum load of 5,865kg. Taxi speed was easily modulated by applying toe wheelbrakes.

Negotiating the ramp

Nosewheel steering provided up to 80¼ of travel in either direction using the handwheel, while rudder pedal control was limited to ±12¼. The nosewheel steering system allowed me to follow taxi lines accurately, and negotiate the tight confines of the ramp area.

Setting the flap handle to the 15¼ detent caused the leading-edge slats to deploy hydraulically and the trailing-edge flaps to extend electrically to 15¼. While holding short of Wichita Intercontinental's runway 19R, Snider confirmed that pre-take-off checks were complete.

Cleared on to the runway, I hit the go-around (GA) button on the throttle. The GA flight-director mode presented a wings-level 13¼ climb attitude with the V command bar. Once cleared for take-off, I quickly advanced the throttles to the take-off/maximum continuous) detent - 86% fan speed (N1) for the 29¼C day. The engines spooled up rapidly and I released the brakes.

Acceleration was impressive - the uprated engines and light gross weight gave a thrust-to-weight ratio of 0.466. Yoke forces were light as I rotated the aircraft to 13¼ at 116kt (215km/h) indicated airspeed. The aircraft lifted off the runway only 19s after brake release and after a ground run of less than 500m. Gear retraction after lift-off and flap retraction at 170kt caused no appreciable change in yoke forces. After reaching 250kt for the initial climb, I retarded the throttles to the climb detent, allowing the FADEC to provide optimum power and relieving the pilot of the task.

Passing 10,000ft (3,050m), speed was increased to 275kt for the climb to 43,000ft. This speed was held until we passed 35,000ft, where a constant M0.83 was held for the rest of the climb. Although the aircraft's ceiling is 51,000ft, a more typical cruise altitude is 43,000ft, where we levelled off only 21min after take-off. FADEC-governed N1 had varied from 90% to 91% during the climb and 458kg of fuel had been used. At maximum take-off weight the climb would have taken about 30min and burned just over 635kg of fuel.

While level at 43,000ft, the throttles were left in the climb detent until M0.88 was reached; then the throttles were retarded to the cruise detent. After3min the aircraft stabilised at M0.9/511kt true airspeed, fuel flow was 917kg/h (2,020lb/h) and the aircraft held 258kt indicated airspeed. Throttles were retarded slightly aft of the cruise detent to slow to and maintain a long-range cruisespeed of M0.85/484kt true airspeed. Total fuel flow was 745kg/h as the aircraft zipped along at over 15km/min.

A series of 45¼-banked steep turns was flown at 250kt indicated airspeed. Bank angle control was precise and no buffet was felt while manoeuvring. After engaging the autopilot, I went into the passenger cabin. The noise level was quite low, and I was able to talk with Dan Grace, the second demonstration pilot, at normal speech levels. The pressurisation system has a maximum differential of 0.641bar (9.3lb/in2) and will hold an 8,000ft cabin altitude all the way up to 51,000ft.

In the event of cabin depressurisation, the autopilot has an emergency descent mode. If cabin altitude exceeds 13,500ft when the aircraft is above 34,500ft, the autopilot will turn the aircraft 90¼ to the left of current heading and begin a descent to 15,000ft, speed increasing to maximum operating (VMO). The aircraft will level at 15,000ft and stay on heading until the pilot intervenes. Even if the pilots were incapacitated, this mode would likely give them time to regain consciousness.

With the high-altitude manoeuvres complete, a descent to 12,500ft above mean sea level was started by pushing the throttles to the climb detent and nosing the aircraft over to accelerate to VMO. At M0.925, the overspeed warning beeper came on, indicating we had exceeded the M0.92 limit. At 280kt indicated airspeed, I did a sharp control doublet in each axis. Responses were well damped.

Passing 18,000ft at 335kt and idle power, the rate of descent was 4,200ft/min. Deploying the six wing-mounted speedbrake panels caused a slight pitch up, and descent rate increased to 6,800ft/min. The X's high speed and speedbrakes greatly enhance its ability to get down quickly from altitude.

Docile when slow

Aircraft gross weight had decreased to 12,390kg when we levelled at 12,500ft. Power was kept at idle and I slowed the clean aircraft at 1kt/s. On the PFD's airspeed tape, a white line indicated 1.3VS (stall speed) - about 136kt - and a red line indicated 1.1VS. A slight increase in wind noise at 118kt signalled automatic deployment of leading-edge slats.

As the aircraft slowed, there was no aerodynamic burble or other natural indication of the impending stall. Both stick shakers, one on each yoke, came on at 115kt (0.83 units on the AoA gauge). The wing remained level as I pulled the yoke to the full aft stop. The aircraft settled into a 3,000ft/min descent in a 5¼ nose-high attitude. Recovery was initiated by releasing yoke back-pressure and flying out of the stall.

Gear and full flaps were lowered in preparation for a landing configuration stall. Power was set to 59% N1 to slow at 1kt/s. The white line for 1.3VS was at 117kt. In a 10¼ nose-high attitude, both stick shakers activated at 98kt, again 0.83 AoA units. As with the clean stall, the wing remained level with no rocking motion throughout the manoeuvre. Recovery from this stall involved maintaining level flight and advancing the power. Thrust from the high-mounted engines helped push the nose over as the aircraft accelerated.

After the stall, while still in the landing configuration, Snider pulled the left engine to idle at 105kt/1.1VS. Using only the right engine, I did a series of 20¼-banked turns. A small amount of rudder was required to co-ordinate the turns, but overall controllability was excellent at such a low speed.

Satisfied with its slow speed handling qualities, we retracted the X's gear and flaps as Wichita approach control vectored us to intercept an instrument landing system final approach to runway 19R. At 6,000ft, the Honeywell TCAS called out "traffic, traffic". The conflicting traffic - a Beech Bonanza at 5,500ft - was clearly shown on the MFD. As we approached the Bonanza's flight path, the TCAS cautioned us to "monitor vertical speed", because any descent would have brought us too close. Only after the TCAS announced "clear of conflict" did we see the Bonanza. TCAS is standard on the 2002 Citation, and proved its worth by greatly improving traffic awareness in the congested terminal area.

The descent was continued to 3,000ft, and flaps set to 15¼ as the aircraft slowed to 150kt. Once established on the localiser, gear was lowered and flaps set to full. At glideslope intercept, about 57% N1 was required to hold a target approach speed of 120kt (reference speed (VREF) + 5kt). Power response was good and the flight director allowed me to track both localiser and glideslope easily. Pitch attitude was relatively flat, the nose on the horizon in a 500ft/min descent.

Crab technique

Because of the X's long wing and short trailing-link gear, a wings-level crabbed approach is flown in crosswinds. There was a slight left crosswind for our first landing, so only a few degrees of crab were required. This crab technique may feel a bit unusual for most pilots who have grown up flying wing-low approaches. Touchdown should be in a wings-level attitude, using the rudder to align the fuselage with the runway just before touchdown.

The flare manoeuvre itself also differs from that of other Citations. Unlike its straight-wing brethren, only a very slight flare - 2-3¼ of pitch change - is required to establish the landing attitude. Also, no attempt should be made to hold the aircraft off the runway with more and more yoke backpressure. Despite these differences, landing the Citation X is easy: just start pulling the power to idle at about 50ft and flare slightly a few feet above the runway.

Once on the runway, I extended the speedbrakes and Snider set the flaps to 15¼ in preparation for the go-around. When flaps were in position, I retracted the speedbrakes and advanced power to the take-off detent. After rotating at 120kt, the aircraft lifted off, and Snider retracted the gear and pulled the right AE3007 to idle to simulate an engine failure. At 135kt it took about 45kg rudder pressure to maintain wings-level on runway heading.

Flaps were retracted in the climb and the aircraft was accelerated to the en-route speed of 190kt. There was enough trim available to zero out rudder forces in the climb, and I appreciated having a conventional slip ball on the lower edge of the PFD. Once level at pattern altitude, I centred the rudder trim and flew the rest of the approach.

The single-engine approach was flown like the two-engined one before it, with 35¼ flaps, but at VREF +10kt (125kt). If climb performance is a concern, 15¼ flaps can be used. Unlike the first approach, where I flared several feet high, this one was on the money, touching down just after the slight flare.

The last approach flown was a visual circuit with both engines. Final approach speed was 120kt. After a smooth touchdown at 115kt, I extended the speedbrakes and lowered the nose to the runway. Firmly on the ground, I selected reverse thrust on both engines and applied the main wheel toe brakes. Deceleration was rapid, even though I was not applying enough brake pressure to cycle the anti-skid. Thrust reversers were stowed at 70kt. With a 7kt headwind, the 11,770kg aircraft was brought to a halt less than 300m from the touchdown point.

Extreme performer

During the 1h 36min flight, I was able to sample the Citation X at the extremes of its flight envelope. It was easily hand-flown at M0.90 and 43,000ft. The well-appointed cabin was quiet even at high cruise speed. Speedbrakes and a M0.92 maximum operating speed allowed the aircraft to get down rapidly from high altitude.

Low-speed performance was no less remarkable. Both the clean and landing configuration stalls were as benign as any I have experienced, the latter occurring at only 98kt. Approach speeds were also low, helped by the wide-span leading-edge slats.

Landing the Citation X was easy, although it required different techniques to other Citations. The world's fastest business jet proved easy to fly at both ends of its wide speed range. Increased engine thrust and higher gross weight are just two reasons why customers looking for a fast jet are likely to consider the upgraded Citation X.

Source: Flight International