AIN Special Reports

Pilot Report: Citation Longitude

 - October 23, 2018, 6:27 AM
(Photo: Textron Aviation)

Textron Aviation’s super-midsize Longitude, the largest Citation yet, is about to enter service. Just before certification, I flew twice in the new Longitude, the first time in the cabin and the second up front on the flight deck.

This was the fifth flight-test vehicle Longitude, which had completed all flight test activities and is now a demonstrator equipped with a production interior. It was a typically warm summer day in Wichita with puffy scattered clouds above 10,000 feet, but otherwise clear with excellent visibility.

In the cabin, the most notable feature is the extraordinarily low noise level. The Longitude cabin has the same flat floor, height, and width (72 by 77 inches) as the Latitude’s, and they share the same nose section and flight deck, but the Longitude’s cabin is 41 inches longer.

Two interior configurations are available: the standard layout with four club seats forward and four in the aft area, or an optional forward club seating section with a three-place divan in the rear opposite two club seats. All of the divan seats can be used for takeoff and landing, and it is certified without shoulder harnesses, although some customers prefer the harnesses and are specifying that they be included, according to Kevin Steiner, technical marketing team lead.

With the divan, total seating capacity is nine passengers plus one more on the jumpseat up front, which can be configured facing either forward or aft. Without the divan, there are seats for eight plus the jumpseat. If the jumpseat isn’t needed, it can be removed and that space used for storage. The divan is berthable, and all of the club seats can be turned into lie-flat beds. Longitude certification will be for a total passenger seating capacity of 12.

Longitude cabin
The standard cabin layout has four club seats forward and four in the aft area. (Photo: Textron Aviation)

The heated and pressurized 100-cu-ft baggage compartment is fully accessible in flight up to the Longitude’s maximum operating altitude of 45,000 feet, with no time limit, and it holds up to 1,000 pounds. Total baggage capacity using all available storage space is 112 cu ft and 1,115 pounds.

Achieving the low noise levels involved more than just adding sound-deadening material, according to Steiner. The pressurization outflow valve is located away from the passenger compartment. Any openings to the outside, such as air scoops, doors, and access panels were evaluated for noise contribution. Internal ductwork contributes to noise, too, and engineers designed the duct attachments and internal structure to minimize cabin noise.

Connectivity for the Longitude includes Gogo Business Aviation’s air-to-ground system, which will soon be switched to the latest Avance L5 version. A Garmin GSR 56 Iridium satcom is also included as standard. One telephone handset is located at the VIP seat and another in the flight deck. A second GSR 56 is installed to provide datalink for FANS and ATN-B1 services, which means that Longitude pilots can take advantage of ground and airborne air traffic control digital clearance delivery and messaging in the U.S. and Europe. For weather information, the GSR 56 can download weather via Iridium satellites. SiriusXM weather is available in the U.S.

During the flight, it was readily apparent that the longer cabin gives Longitude passengers much more legroom (30 inches). Conversing, with people sitting at either end of the cabin was easy in the super-quiet environment.

Each of the comfortable seats is equipped with controls for lights, window shades, and the entertainment and cabin management system (CMS). These can also be managed with a mobile app. USB ports are also installed at each club seat. Each divan armrest holds two drawers, measuring 6.5 inches deep, and there are three large drawers under the divan.

Pleated window shades can be opened partially or fully or put into a shear mode, which allows partial light to enter through the large windows without admitting full daylight.

Cabin altitude is 5,950 feet at the Longitude’s 45,000-foot maximum operating altitude.

The galley has a sink and hot- and cold-water faucet, and room for an espresso maker and microwave oven, plus a master control panel for the CMS. The panel allows selection of preset scenes of lights, cabin temperature, and shade positions. A media server is mounted opposite the galley, but this will be replaced by a Gogo Vision entertainment system once the Avance L5 connectivity system is certified.

The galley counter varies from 16 to 18 inches deep and is 63 inches long. Cabinets are 13.5 to 14.5 inches deep. Behind the sink is a storage area for wineglasses and regular glasses, covered by an opaque sliding door. More storage is located under the galley counter, including a generous ice drawer, utensil storage, slide-out shelves, and a wine-bottle drawer.

Opposite the galley is more storage, including a tall cabinet with removable drawers.

A main cabin door curtain, which must be open for takeoff and landing, further cuts noise levels in the galley and cabin. I measured noise levels in the cabin using the dB Meter Pro iOS app on my iPhone. While this obviously isn’t the same as real noise testing equipment, it does show some interesting comparisons. Cabin noise levels, for example, ranged rom 62 to 65 dB, depending on location. Inside the baggage compartment, noise rose to 80 dB. In the galley with the door curtain closed, the app showed 68 dB, and 67 dB in the flight deck. With the curtain opened, the noise level rose by 3 dB in the galley/flight deck and by a similar amount in the cabin.

There is a new feature on the Longitude that sets it apart from any other Citation; it is equipped with two lithium-ion main-ship batteries. These are True Blue Power TB-44s, 44-amp-hour types using stable Nanophosphate cell chemistry. According to True Blue Power, the two batteries shave 100 pounds off the Longitude’s empty weight and are expected to provide a 90 percent reduction in battery maintenance costs.

This isn’t the first time that Cessna delivered a Citation equipped with a lithium-ion main-ship battery. The CJ4 was so equipped when first delivered, but its lithium-ion battery (made by another manufacturer) was replaced with lead-acid or nickel cadmium batteries following a 2011 incident and airworthiness directive due to an incorrectly connected ground-power unit.

Focus on Flying

Demo pilot Stuart Rogerson showed me some details of the Longitude during a preflight walkaround.

While the noses of the Latitude and Longitude are the same, there are some subtle differences. The Longitude’s AC-powered windshield, which heats differential panels instead of the entire pane, can be powered by the auxiliary power unit (APU) or ground power. That is not the case for the Latitude. The Longitude has dual AOA vanes for the stick pusher and in a first for a Citation, ice-detection probes. The Longitude is the launch customer for Garmin’s GWX 80 Doppler digital weather radar.

For overwater operations, which are more likely for the 3,500-nm Longitude, dual oxygen tanks are mounted in the nose compartment.

As in most modern business jets, all lights are LEDs. The taxi light is usable as a backup for landing in case the landing light fails. All access panels have courtesy lights that switch on when the panel is opened. These lights are powered by one of the TB-44 batteries, leaving the other battery for starting the APU.

New for the Longitude is a fuel computer mounted at the fuel access panel, which allows control of single-point refueling without having to monitor from the flight deck.

Longitude cockpit
The front office of the Longitude employs the Garmin G5000 flight deck. (Photo: Textron Aviation)

The Longitude’s flight control system is similar to the Latitude’s, with mechanically controlled ailerons and elevator (with trimmable stabilizer) and fly-by-wire rudder and spoilers. There are three spoilers on the left and right wing, with the middle and outboard panels for roll control and all three for speedbrakes and ground spoiler operation. The yaw damper is in effect all the time and there is no switching it off on final approach. In a one-engine-inoperative situation, the rudder automatically biases to adjust for the inop engine, although the pilot still has to step on the rudder and thus remains in the loop during single-engine operations.

In case extra power is needed during a hot-and-high situation with one-engine-inoperative, the good engine is capable of delivering a power boost for up to 10 minutes, or with both engines running, for five minutes, which would be helpful during a windshear encounter. Following a power boost, a maintenance log entry is required.

Icing protection is standard bleed air for wing leading edges and engine inlets, and an electro-mechanical expulsion deicing system deices the empennage.

The dual hydraulic carbon brakes are brake-by-wire, and all brakes are available for emergency braking. Nosewheel steering is via tiller, the same system as the Latitude, and allows for steering up 80 degrees. The nose can steer up to 9 degrees using the rudder pedals.

Engines are Honeywell’s HTF7700L, each delivering 7,600 pounds of thrust. The Honeywell 36-150 APU can be run up to 35,000 feet.

The Longitude’s trailing-link landing gear sits the airframe fairly low, so there is no need for a ladder to access the aft baggage compartment from the outside.

An interesting aspect of the fuel tank design is that it uses a transfer system to move fuel from tank to tank, instead of a slower crossfeed-type system.

The Garmin G5000 flight deck’s new GHD 2100 head-up display with enhanced vision system—Garmin’s first HUD—will not be available on the Longitude at entry into service, but will be a follow-on certification. Rough cost of the optional HUD/EVS is $500,000 to $600,000, and plans are to seek approval for lower approach minimums when using the HUD/EVS. Although test pilots have flown with the Garmin HUD extensively, it wasn’t installed on the Longitude that I flew.

Like the Latitude’s, the Longitude’s flight deck is designed for simplicity and ease of use, with minimal clutter. Much of this is due to the Garmin GTC 570 touchscreen controllers, which consolidate many functions that used to be managed with knobs, switches, and buttons. There are four touchscreen controllers, two in the center console and one each on the left and right side. The controllers are the infrared touch type, and thus can be manipulated while wearing ordinary gloves or with the end of a pen or pencil. They are designed to prevent accidentally actuating adjacent buttons.

Automated Process

Many of the tests that take a lot of time and knob manipulation in older Citations are automated in the G5000-equipped jets, and this speeds up the time to get the Longitude ready to fly. Some tests by the pilot are still required, however, such as the stick pusher, engine and baggage fire loops, overspeed, and annunciators. Within minutes we had the HTF7700Ls running and were ready to taxi.

Rogerson plugged in a flight plan to the north of Wichita’s Dwight D. Eisenhower National Airport. He manually set the bug speeds because the Longitude takeoff and landing data won’t be finalized until just after type certification.

Takeoff weight was 31,149 pounds, with two pilots and one observer. That’s 8,351 pounds (21 percent) below the 39,500-pound mtow. The Longitude’s full-fuel payload 1,600 pounds.

I taxied to Runway 18L. The Longitude’s tiller steering is firm and precise, and although this jet has a fairly long fuselage, I didn’t feel any jerkiness in the tiller. The carbon brakes actuated smoothly with no grabbiness.

The Honeywell engines gave us a snappy acceleration during takeoff, and I lifted the Longitude off smoothly, with very little pull on the yoke needed to escape the runway. Pitch forces are lighter at low speed but get heavier as the jet speeds up; a bit of trim keeps everything well under control.

We climbed to FL430, with a brief stop at FL260 for traffic. Passing FL200, the rate of climb was 2,550 fpm. In the middle and higher altitudes, temperatures were ISA + 14 deg C until above FL400. Then they cooled to ISA -4 as we leveled off at FL430. Cabin altitude was 5,400 feet and with power set at max cruise and fuel flow 860 and 880 pph, the Longitude settled at Mach 0.83 and 473 ktas. Maximum operating speed is Mach 0.84.

Low-altitude Airwork

After the cruise check, we turned back toward Wichita and descended to 12,000 feet for some airwork. During the descent, I pulled the power to idle and pushed the nose down, then watched the airspeed climb rapidly toward the red on the PFD. At that point, the Garmin flight control system pulled the nose up to reduce the speed. I actuated the speedbrakes to help us slow down, and they came out with nary a rumble nor any aerodynamic bump, thanks to the fly-by-wire control. The speedbrakes can be set at any intermediate setting and the pilot can move the control quickly, without causing the boss’s drink to spill.

Back at 12,000 feet, I started with steep turns, with a 360 to the right at 45-50 degrees, then a 180-degree turn to the left. The Garmin autothrottles easily maintained the necessary added power for the selected speed during the steep turns, but I did need to pull the yoke aft firmly to keep the nose up. This is all made easier by the flight path marker (FPM) on the G5000 primary flight display (PFD), like having a HUD but on a head-down display; just keep the FPM on the zero pitch line, and there is no change in altitude.

We then set up for some approaches to stall, with autothrottles off, but Rogerson advised not going to stick pusher because the rapid nose-down push might cause fluid in the vacuum lavatory to spill. For the first maneuver, I slowed straight-and-level and in clean configuration all the way to stick shaker, then reduced the angle-of-attack (AOA) and added power, with a minor loss in altitude. I did another approach to stall in clean configuration but in a 30-degree turn, then recovered at the shaker by reducing AOA, leveling the wing, and adding power. The engines responded fairly quickly to the application of power. At lower speeds, lateral control is much lighter and more pleasant, harmoniously matching the lighter pitch control feel.

Rogerson extended the landing gear and set flaps to full, and I slowed the Longitude down so I could experience the final approach attitude, which is pretty flat at a 3-degree glidepath angle. The approach configuration near stall was gentle with zero wing rock as the shaker shook the controls and I recovered back to straight-and-level flight.

Returning to Wichita, we set the G5000 for the ILS to Runway 18R. I hand-flew the approach, coming in slightly high, but with full flaps, I was easily able to descend the Longitude onto the proper glidepath, which indeed did look shallow. Rogerson advised that near touchdown I would need just a tiny bit of nose-up pitch to arrest the descent, but I should be careful not to flare too high, otherwise the Longitude will float. At 50 feet, the autothrottles automatically retarded to idle. While covering the throttles with my right hand, I kept flying down at the runway. Moments after I barely checked the pitch-down attitude with a tiny aft movement on the yoke, the main wheels touched smoothly, followed by the nosegear.

Rogerson set the flaps for takeoff, and I advanced the throttles for a touch-and-go, and this time it felt like the Longitude leapt off the runway. We flew back around for an RNAV 18R approach, which felt much the same as the ILS, with the same flat attitude on final. The second landing was similar to the first, although I tried to prevent dropping the nose as quickly this time.

For the third landing, Rogerson set a visual approach, a recent new feature for the G5000 avionics that allows pilots to create a 3-degree glidepath to the end of any runway. This is a great tool to help ensure arrival at the proper runway, especially where no straight-in approach is available.

I elected to try to stop shortly and Rogerson said to feel free to brake heavily, without using reverse thrust. After touching down and lowering the nose, I thought I was giving the brakes a good workout, and the Longitude seemed to come to a fairly quick halt, but he said I wasn’t really standing on the brakes very hard.

It’s been a few years since I flew the Latitude, and overall the Longitude flies similarly in terms of handling and pilot interface. But the Longitude steps up Textron Aviation’s game in cabin comfort and performance, with refinements in the aircraft systems as well, making the Longitude a well-qualified candidate as the largest and most-capable Citation.