Why Cessna’s flagship Longitude is degrees better

Despite the global Covid-19 pandemic, the super-midsize segment of the business jet market is showing signs of life. This is in part being driven by an uptick in demand for fractional jet operators, as businesses and the well‑heeled have flocked to their services in order to avoid the perceived risks of travelling via scheduled airline operations.

Bombardier continues to be the market leader in this segment – based on deliveries and orders – with its Challenger 300/350 offerings. Dassault and Gulfstream also maintain a strong presence, with their Falcon 2000S and G280 models, respectively. And from a technological viewpoint, Embraer’s Praetor 600 is the stand-out offering, with a full fly-by-wire (FBW) flight-control system and available head-up display.

Textron Aviation’s Cessna brand, which popularised business jet travel with the Citation series, has the newest entry into this market area, having launched its Longitude at the NBAA convention in November 2015. The ambitious goals for the Longitude were to offer transatlantic range while providing the segment’s best cabin experience and lowest operating costs. First flight of the aircraft was in 2016, with initial customer deliveries made in the fourth quarter of 2019.

To accomplish these lofty goals, Textron Aviation leaned heavily on its past successes when designing the Longitude. While it is a unique design, the new flagship shares its flightdeck and forward fuselage with the smaller and shorter-range midsize Citation Latitude. The fuselage also has the same cross-section as its stablemate, but the passenger cabin is 1.1m (3ft7in) longer, to allow for accommodation of up to 12 passengers.

BIG SWEEP

The wing is a clean-sheet design with a sweep of 28.6°; an angle exceeded only by the Citation X+ in Cessna’s Citation line-up. The wing sports a fixed leading edge as well as gently upturned winglets that add 1.33m of span on each side. The 0.89m-tall winglets are the most prominent of any Citation. The mildly supercritical wing combines with efficient Honeywell HTF7700L engines – each rated at 7,660lb thrust (34.1kN) – to enable a maximum range of 3,500nm (6,480km) while carrying four passengers at Mach 0.80.

While the Longitude has many notable design features, where it really shines is in passenger accommodation. As with all great things, it starts at the foundation, or floor in this case. The Longitude has a flat floor with 1.83m of over-aisle headroom. Typical cabin configurations are a double club arrangement (four seats each), or a club forward layout with a three-place couch and two facing seats in the aft area. The facing seats are berthable, as is the couch.

Forward of the seating area, opposite the aircraft entry door, is a wet galley. All configurations have a spacious lavatory at the aft end of the cabin. In-flight access to the tail cone baggage area is through a door on the lavatory’s aft wall.

While the spacious cabin and its appointments are pleasing to the eye, it is what is unheard that truly enhances the cabin experience. At cruise conditions, Cessna says the Longitude has the quietest cabin in its class. While typical super-midsize cabins have an ambient noise level of 69-72 dBA, the Longitude’s is slightly over 67dBA. It must be remembered that decibels are a logarithmic scale, so even a one- or two‑unit difference would be appreciated.

The Longitude’s interior is further enhanced by its 9.66psi/666hPa differential cabin pressurisation system. It provides a 5,950ft cabin pressure at its maximum operating ceiling of 45,000ft; a level several thousand feet lower than most of its competitors.

CLEAN AIR

Rounding out notable cabin enhancements is the type’s partial recirculation system. Cabin air is sourced from the engines’ bleed air system, whose high temperatures sterilise the air. This clean air is then cooled (conditioned) before distribution in the cabin. After coursing through the cabin, 78% of the air is vented overboard via outflow valves at the rear.

The remaining air is recirculated/returned to the cabin, a common practice that reduces engine fuel burn. Return air is pushed through a HEPA filtration system – which can capture microscopic particles smaller than the Covid-19 virus, and should prevent the reintroduction of contaminated air to the passenger cabin.

Textron Aviation’s close attention to the passenger cabin did not prevent it from also making the Longitude’s flightdeck a great place to work. As mentioned, the model shares a common flightdeck with the smaller Latitude. Its Garmin G5000-based avionics suite features three 35.6cm (diagonal) wide‑format LCD screens across the instrument panel: two primary and one main flight display (MFD).

As with the Latitude, four GTC575 touchscreen controllers (TSCs) are handily placed in the cockpit. Navigation within a main display is via cursor control sticks on the bezel of the TSC.

One neat feature resident in the TSC is the ability to use its screen as a track pad. The flight guidance panel (FGP), to control the autopilot (AP) and flight director (FD), is mounted on the centre of the glare shield. A single-gauge electronic standby flight display, with an internal back-up battery, is mounted between the FGP and the MFD.

Garmin’s synthetic vision technology comes as standard, as does an auto-throttle (A/T) system. As with the Latitude, the small overhead panel hosts lighting control switches.

The Longitude’s flight-control architecture is illustrative of Textron Aviation’s incremental approach to new technology. When Embraer developed its Legacy 450/500 (now enhanced as the Praetor 500/600), it did so with a full FBW control system. I think a well-executed FBW flight-control system can be extremely competent, with the potential to offer envelope protection schemes and enhance performance. Providing these same enhancements in a conventionally-controlled aircraft (with either pure mechanical or hydro-mechanical control surfaces) is a more daunting task.

Textron Aviation has taken measured steps in incorporating FBW technology into the Longitude. The aircraft has mechanical ailerons and elevator, while incorporating a FBW-controlled rudder. This is Cessna’s second commercially fielded FBW primary control surface: the first being the Citation X’s upper rudder. Interestingly, Bombardier’s first FBW primary control surface was the CRJ900’s rudder, while for Embraer it was the E170’s elevator.

The Longitude’s open-loop FBW scheme schedules rudder deflection as a function of airspeed, while performing full-time yaw damper and turn co‑ordination functions. Six wing-mounted spoiler panels – three per side – are the Longitude’s other FBW control surface. These secondary surfaces augment roll authority, act as speed brakes (SBs) while airborne, and dump lift on the ground to enhance wheel brake performance. These three functions are quite routine, with the FBW implementation reducing mechanical complexity and weight.

Runway performance is also enhanced, as an auto-deployment schedule is programmed.

Envelope protection schemes have long been a strength of FBW control systems, and advances by Garmin are making these same features available to conventionally controlled aircraft. The company’s electronic stability and protection system offers attitude protections in both pitch and roll, along with high- and low-speed protections. For the Longitude’s G5000 avionics suite, however, Textron Aviation elected to implement high- and low-speed protection schemes that utilise the AP and/or A/T.

There were 31 Longitudes in service as of late 2020, and in early January FlightGlobal was given the opportunity to see if the type has achieved its goals and can be classed as another Textron Aviation and Cessna “sure thing”.

Our preview aircraft was the 33rd example produced, with the US registration N233CL. I accompanied Textron Aviation senior pilot David Bodlak during the pre-flight walkaround inspection on the ramp at San Jose International airport in California.

SUSTAINABLE FUEL

While the gleaming heated leading edge of the wing caught my eye, it was an “SAF” logo near the door that grabbed my attention. Textron Aviation gives its turbine-powered aircraft customers the option to have their purchases delivered using sustainable aviation fuel: Jet A/A-1 fuel made from sustainable sources.

Currently there is a cost premium for using SAF, but according to the airframer users can take comfort in knowing that carbon emissions can be reduced by up to 80% compared with fossil fuel. Our preview flight would be conducted with SAF, a facet that would be operationally transparent to me.

The inspection was a snap to complete, with only the fuel panel access door needing to be opened to check engine and auxiliary power unit (APU) oil levels.

As I settled into the Longitude’s left seat, Bodlak started the tail-mounted Honeywell APU and put its generator online. With the flightdeck powered, he guided me through its initialisation, loading our route of flight and determining take-off performance. With an electronic checklist still under development, we used a paper one to ensure required pre-start items were accomplished.

APU bleed air was used to start both engines, with the FADEC-controlled starts stabilising each at IDLE in under 30s. The Longitude’s nose-wheel steering tiller fell readily to hand as I negotiated the first 90° turn out of the chocks. During the taxi from the ramp to runway 30R for departure, I was able to track our position on the map display. Flaps had been set to “2” in preparation for take-off.

Once the aircraft was on the runway and cleared for take‑off, I released the toe-actuated wheel brakes and advanced both thrust levers (TLs) to the “TO” detent. The FADECs set take-off power of 89.3%, and the Longitude raced down the runway. Bodlak called “Rotate” at 110kt (203km/h) and I found yoke forces needed to attain lift-off pitch attitude were moderate.

With a take-off weight of 14,270kg (31,400lb), including 3,420kg of fuel and three occupants, our aircraft needed only 1,016m of runway. At its 17,917kg maximum take-off weight, the Longitude would require a field length of 1,466m at sea level on a standard day.

Control yoke force changes during clean-up and acceleration to our initial 200kt climb speed were low and easily countered with yoke-actuated pitch trim. I followed the FD’s guidance as we proceeded on the TECKY 3 RNAV departure. During the turn to the southeast, I found lateral control forces, while well harmonised with pitch forces, were higher than I would have liked. I was, however, pleased that, unlike other Citation Jets I have flown, the yoke itself was at a comfortable height when seated at the design position.

As we climbed to our planned cruise altitude of 41,000ft, I engaged the AP and refamiliarised myself with the avionics suite. While I am still finding my way learning all the Garmin system’s nuances, I marvel at its capabilities and the flexibility of its interface. Textron Aviation’s decision to put the G5000 in the Longitude will certainly please the generation of pilots who have grown up in the Garmin ecosystem.

Once level at 41,000ft, we endeavoured to do a number of cruise points, to spot-check published performance figures. Mountain wave activity near the Sierras prevented us from obtaining accurate data, but we did manage a maximum cruise speed point. At a gross weight of 13,555kg, a total fuel flow of 2,050lb/h held an indicated M0.839; just shy of maximum operating Mach (MMO) speed. Our indicated airspeed of 250kt translated to a true 476kt, under ISA -2°C test day conditions.

Following the flight, Bodlak provided book numbers for a 17,237kg aircraft at M0.84 and M0.79 (long range cruise). True airspeed at the MMO condition would be 477kt, with a total fuel flow of 2,122lb/h. At the long-range condition, true airspeed would be 451kt and fuel flow would drop to 1,820lb/h.

With four passengers, a range of 3,500nm at M0.80 is listed for the Longitude. So what are the type’s real world capabilities? Transatlantic flight is no problem, such as Columbus, Ohio, to Paris. Late for the opera after checking out of the Raffles Hotel in Singapore? No problem, as Sydney is just a nonstop flight away.

Before I left the flightdeck to sample the Longitude’s passenger accommodation, I slowed the aircraft to M0.80 and noted the pressurisation system was holding the cabin altitude at just 4,900ft; remarkably low for this flight level, this contributes to less fatiguing and more comfortable journeys.

As I walked back through the cabin I noted that the surface was level, easing transit of the long, flat-floored space. Subjectively, it was one of the quietest business jet cabins I had been in, with Textron Aviation’s data backing up that impression. The quietest area was the second row of the forward club seating area, with the ambient level increasing fore and aft of there. I sat in the forward club area and chatted with our safety pilot, Alan Pitcher. He and I had flown together on my Citation X+ preview flight out of Wichita, Kansas, in 2014. We were able to converse at normal voice levels and I enjoyed the opportunity to catch up with him.

SAFETY FIRST

After I returned to the flightdeck, Bodlak and I discussed the AP’s emergency descent mode (EDM). At 30,000ft or above, loss of cabin pressure with the AP engaged will trigger EDM. The AP will start a descent and accelerate the aircraft to MMO/maximum operating speed. Additionally, the A/Ts will set IDLE thrust to speed the descent to 15,000ft, where the AP will level the aircraft and A/Ts maintain a safe speed. This feature is a great safety enhancer and available inall G5000-equipped Citation aircraft.

Next, we started a hand-flown descent towards a medium altitude block (15,000ft-17,000ft), where we would investigate some of the Longitude’s slow speed protection schemes. Taking advantage of our high potential energy, I tested two of the business jet’s high-speed protection schemes during the descent. The first used the A/Ts, which had been turned off with the TLs themselves about mid-range. I ignored the several aural and visual warnings as the speed approached MMO. Before reaching M0.84, the A/Ts woke up and retarded the TLs to IDLE in an effort to prevent an overspeed. Next, I engaged the AP and let the Longitude stabilise below MMO.

While still in a descent I pushed the TLs up to again speed the aircraft towards MMO. This time I held them firm so the A/Ts could not retard them. As the speed increased to M0.84, the AP pitched the Longitude into a 1,000ft/min climb, to prevent it from exceeding MMO.

Level in the medium altitude block at 300kt indicated airspeed, I extended the SBs. As they deployed, the aircraft started to pitch up, requiring about 9kg of forward yoke pressure to maintain level flight. Next I retarded the TLs to IDLE to speed the deceleration rate. Passing 250kt I pushed the TLs up to accelerate back towards 300kt. Giving primacy to the advancement of the TLs as an indication of my intent, the SBs were automatically retracted. Pilots are more likely to drop the SB lever out of their cross-check than the TLs.

Automatic SB retraction is a safety-enhancing feature that should not be overlooked. There is strong speculation that if the Boeing 757 had had such a feature, it might have allowed American Airlines flight 965 to climb over high terrain and prevented the deadly accident in December 1995 near Cali, Colombia.

The last medium-altitude events we conducted were two approach to stalls, one in a clean and the other in a landing configuration, with gear down and flaps at FULL. As with the high-speed case, the A/Ts will wake up to prevent a speed excursion, in this instance increasing power to prevent a stall. To disable this feature, the A/T circuit-breaker was pulled, allowing the Longitude to slow at IDLE power in near level flight.

In both configurations the aircraft was responsive to small amplitude control inputs as it slowed towards shaker onset speed, represented by 0.85 units of angle-of-attack. Little if any airframe buffet preceded shaker activation, the indication of an impending stall. Simultaneous relaxation of aft yoke pressure and advancing the TLs recovered the Longitude to normal flight conditions for both configurations.

Pleased with the Longitude’s low-speed handling, we headed towards KLIDE, a point on the RNAV (GPS) Y30L for our recovery back to San Jose. I engaged the AP and A/Ts and monitored their performance as the Longitude expertly flew the coupled approach.

Our ownership position on the MFD map display allowed me to easily keep track of our lateral position. While vertical track position can also be monitored on the map display, it is not always intuitive. Fortunately, the G5000 has a vertical situation display (VSD) that presents a profile view of the desired vertical path. Onour initial turn towards KLIDE, reference to the VSD quickly alerted us that we were higher than planned – a situation rectified by deployment of the SBs.

Once fully configured on final, the A/Ts accurately maintained our approach speed of 124kt. At 257ft – localiser performance with vertical guidance minimums – Bodlak called for a go-around and Isimultaneously clicked off the AP and ATs. Next, Ihit the throttle-mounted take-off/go around (TOGA) switch and called for Flaps to “2” as I advanced the TLs to the TOGA detent. Following FD guidance established an initial climb and I called for gear retraction.

Once safely away from the runway in a 120kt climb, Bodlak simulated an engine failure by pulling the right TL to IDLE. While we had pre-briefed this manoeuvre, it did catch me by surprise, adding to the realism of the scenario. About 25kg of left rudder pedal was needed to keep the Longitude on runway heading as we climbed towards pattern altitude for a visual circuit.

The right TL was kept at IDLE throughout the simulated one-engine approach and landing. Landing configuration was the same as for the previous two-engined RNAV approach. With the rudder trim centred, less than 5kg of pedal pressure was needed to maintain co-ordinated flight at a final approach speed of 124kt.

After a smooth touchdown, I applied moderate wheel braking and deployed both thrust reversers (TRs). Deceleration on the dry runway was quite good, with the Longitude stopping before I had a chance to stow the reversers. A number of aircraft I have flown have a pilot-observed minimum speed by when the TRs must be stowed. This can be driven by a number of factors, including prevention of foreign object ingestion, damage to the aircraft, and controllability concerns.

STOPPING POWER

The Longitude’s FADEC-controlled engines take care of this problem for even the most inattentive pilot. With TRs deployed, as the aircraft slows the FADECs reduce engine thrust to safe levels regardless of the actual TL position. On a contaminated or slippery runway, this feature should prove a big asset, with every bit of stopping power harnessed without worry.

My 2.3h in the Longitude provided a real window into its capabilities, and the flat-floored super-midsize Citation did not disappoint.

The Longitude offers transatlantic range and an outstanding cabin experience: passengers will appreciate the large cabin and class-leading acoustics.

Textron Aviation’s measured adoption of technology for aircraft systems and the use Garmin’s powerful G5000 avionics suite combine to create an aircraft that pilots will enjoy flying. While not evaluated during my flight, the company reports that the type has the lowest direct operating costs of any super-midsize jet.

As such, the Longitude has attributes sure to please its core stakeholders, and it looks like Cessna has indeed fielded another “sure thing”.