Honeywell improves Apex capabilities
Upgrade gives Pilatus PC12NG increased functionality.
By Woody McClendon
ATP/Helo. Challenger 604, Bell 222/412
Honeywell PC12 Program Test Pilot Capt Kevin O'Hara (L) and Pilot Author Woody McClendon fly the PC12. The formidable terrain near Sedona AZ is visible out the windshield and on the 3 Honeywell Apex cockpit displays.
Pilatus's PC12 has a unique place in the aviation market. Largest by far of the single-engine turboprops, it has built a following among owner pilots who have a need for its large cabin and flexible operating envelope. The PC12 has also become a workhorse in the aeromedical community.
As it replaces older turboprop twins, it's won the hearts of medical crews who value its expansive cabin and of those in financial roles who appreciate its lower operating costs.
The law enforcement community has adopted the PC12 as an aerial reconnaissance platform. Federal, state and local agencies are using it in venues ranging from cities and towns to, in the case of Immigration & Customs Enforcement, the entire US/ Mexico border. The US Air Force is even operating the PC12 in a special ops role.
First certified in 1994, the PC12 has had several evolutions, the latest—PC12NG—distinguished by its larger variant of the P&WC PT6A-67P and the newest version of Honeywell's Primus Apex avionics suite.
Honeywell Commercial Avionics officials in Phoenix AZ recently provided a briefing and a flight demonstration of the synthetic vision system (SVS) enhancement option. The update is now certified and available to PC12 owners.
Avionics Product Marketing Dir Warren Nechtman introduced PC12 Program Test Pilot Kevin O'Hara and Falcon EASy Program Chief Test Pilot Sandy Wyatt. Wyatt explained that Honeywell's Technology Group had decided to do more than just install an SVS in the PC12. They viewed it as an opportunity to offer Pilatus owners a new energy management tool, further increasing the utility and flexibility of the airplane.
The key was to apply Honeywell's head-up display (HUD) technology in developing the new SVS-based head-down view in Apex. To that end the modified symbology set that's part of the SVS upgrade incorporates the infinite focus typical of HUD applications.
The SVS terrain view is superimposed "behind" the HUD-type symbol set. The advantage to the pilot is flightpath cues overlaid on the flight director command bars, providing an optimized blend of desired energy state with computed steering commands.
Two cues, painted in green in keeping with Apex symbology standards for advisory information, are found on the SVS-enhanced PFD. The first is the flightpath symbol, computed using angle of attack, airspeed and acceleration data from the Apex attitude and heading reference system (AHRS) and the Apex air data module.
Wherever the flightpath symbol is on the PFD—now with the SVS terrain display in the background—is where the aircraft is going to arrive.
When the pilot is setting up an approach, computed flightpath information can be the difference between a smooth arrival and an unstable one. Thus, flying the aircraft flightpath symbol to overlay the flight director command bars is, in essence, using flightpath as the primary input.
Old way vs the flightpath way
Older versions of situational displays offer only positional scales of vertical and horizontal deviation. Pilots must then derive maneuvers to correct for these deviations. Those of us who have flown with these less sophisticated instrument arrays have painful memories of struggling with pitch, roll and power in order to arrive at the end of the runway in a condition from which we could hopefully execute a safe landing.
The 2nd cue in the HUD-based symbology is an acceleration pointer. Also painted in green, it displays acceleration along the longitudinal axis. Wyatt explains that, in essence, the acceleration cue points to where flightpath is going to be. Thus, if we were to reduce power, the acceleration cue would move down, as would the flightpath as soon as the total energy of the aircraft reflected the reduced power.
Placing the flightpath symbol precisely on the approach end of the runway generates flight director commands that will put the aircraft on the selected profile. Once the path is stabilized, the flight director command bars, flightpath symbol and acceleration cue will all be aligned on the display.
As wind and other exterior forces affect the flight, the path symbol will move, defining the new point on the terrain that will result. In a continuous closed loop process the pilot can repoint the path symbol at the desired location on the terrain, then follow the command bars to adjust the flight controls and achieve the corrected path.
Wyatt compares this sophisticated method of path control with the older one of trial and error. "In the past," he explains, "when we were doing a visual approach, we'd aim the airplane at the runway, then make corrections to the raw site picture for what were really flightpath variations.
If everything went well we'd arrive at the runway end with only minimal corrections, but a large wind component or turbulence could well find us struggling to maintain a smooth flightpath. And too many accidents have happened when pilots simply couldn't adjust to variances in terrain, wind and weather. The flightpath display that's part of the SVS upgrade ends that."
We departed DVT (Deer Valley AZ) late in the afternoon and headed north to SEZ (Sedona AZ), one of the more scenic airports in the Southwest and ideal for looking at a difficult visual arrival coupled with a challenging missed approach.
The weather was clear, and the wind near calm. O'Hara had set up a VFR route from DVT to SEZ at 10,500 ft MSL. He also programmed a vertical profile that would position the PC12 at BOWSU intersection, one of the IAFs on the GPS Rwy 03 approach.
All this was accomplished via the cursor control device (CCD)—basically a mouse modified to give the pilot a firm grip on the pointing buttons in flight. Scanning dozens of menus and entering data is no more complex than using an iPhone, and almost as easy as working with the latest in laptop computers.
AFCS and approach guidance
The Apex AFCS in the PC12 offers all the usual operating modes in lateral and vertical flight, all easily selectable from a centrally mounted glareshield control panel. As we turned onto the final approach at EXUTY intersection and lined up with the runway, O'Hara set the power for a nominal approach speed of 95 KIAS.
The Apex AFCS flew the computed vertical path, and the flightpath cue indicated that we would arrive precisely at the prescribed touchdown zone (TDZ). Given that the winds were light and variable, there was little opportunity to observe the flightpath computation offering any input other than a stabilized descent.