Category III landings come to bizav

 - September 27, 2006, 12:47 PM

Landings to below Cat I and II ILS minimums have been possible for more than three decades, but the price of admission until recently has been autoland certification of the aircraft and crew. This requires an autopilot with triple-redundant channels in all three control axes, autothrottle with comparable redundancy, nav radios with backup for the backups, as well as intensive and frequent training and currency requirements for pilots of what have been almost exclusively airliners.

The cost has kept autoland operation down to, well, a minimum except in parts of Europe where frequently soupy weather makes it a necessity for operating at all. For most of the corporate and regional-airline world, autoland capability has been out of reach.

Until now.

A blend of ever more powerful computer technology, advanced head-up display (HUD) systems with highly intelligent symbol-generating processors and state-
of-the-art inertial reference systems–along with some clever software writing–has produced a HUD/airplane combination that can be hand-flown down to Category IIIa minimums by any pilot capable of keeping the crosspointers of an ILS indicator centered.

This combo is the Rockwell Collins (Flight Dynamics) 5600 dual head-up guidance system (HGS) on the flight deck of the Embraer E195 jetliner. JetBlue has ordered the recently certified installation on 100 aircraft, with an option for 100 more.

The HGS interfaces with the 100+-seat jet’s Honeywell Primus Epic integrated avionics suite, which includes digital autopilot, autothrottle, flight management system (FMS) and, most significantly, dual inertial reference systems (IRS). The IRS virtually obviates the need for radio beam tracking. It “knows” where the airplane is with reference to the surface, its groundspeed, acceleration, vertical rate, heading, attitude and where it will be if it continues on its present path. Adding to the data mix are Arinc 429 and ASCB digital outputs from EGPWS, flight director, nav radio, air data computer, DME and TCAS sensor systems.

With all this input, the 5600 HGS presents guidance to the pilots through a primary flight display projected on the combiner glass. In the dual setup each HGS is independent, with modes selected through the pedestal-mounted multifunction CDU on the same side as the HUD. The HGS offers guidance cues from taxi through takeoff, climb and every phase of flight, down to a precise touchdown.

Pilots can select to leave the autopilot engaged or hand-fly the aircraft in cruise. Hand-flying is surprisingly easy simply by following the aiming circle on the HUD glass at the center of the projected PFD. This responsive handling is a function of clever control laws written into the E195’s fly-by-wire flight-control system.

In late August, shortly after the Embraer E195 completed FAA certification flights, Embraer and Collins hosted a demonstration of the dual head-up guidance system, staging out of Flightcraft at Portland, Ore. International Airport (PDX). The aircraft was packed with monitoring equipment, and its interior was a far cry from the passenger configuration it will eventually receive.

On board were the Embraer certification flight crew, a pair of high-time Brazilian pilots, several Rockwell Collins engineers and two aviation journalists. The first writer, a former Navy jet fighter pilot with recent experience flying HUD-equipped business jets, flew the aircraft from the right seat from Portland to Yakima, Wash., guided by the HGS cues right down to landing.

Then it was my turn.

Although I hold a commercial pilot’s license with instrument rating, it was my first time on the flight deck of an air transport jet, much less at the controls of one. Embraer’s chief test pilot, in the left seat, directed me to advance the throttles and taxi for takeoff while he took care of programming the HUD, FMS, tuning the radios and doing all that was necessary to get the aircraft ready to fly.

The HUD taxi cues were easy to follow, and with the “real” pilot on the nosewheel steering, the E195 was cleared for takeoff and lined up on the centerline. To my surprise the captain said, “Go ahead, open the throttles and take off.”

Concentrating fully on the HUD speed and attitude cues while the captain set target airspeeds and altitudes with a couple of keystrokes on the CDU, I soon got the knack of keeping the larger steering circle over the smaller heading and pitch target cue on the combiner glass. Two-thirds of the way through the 20-minute flight back to PDX I was quite comfortably maintaining course and altitude solely by flying the HUD cue.
As we descended through 8,000 feet, setting up an approach to Runway 28R, I expected that the captain would take over. Instead he said, “Go ahead, keep flying.” The 5600 HGS can deliver several levels of approach precision depending upon the mode selected. The Category IIIa approach is hand-flown after selecting the “HUD A3” mode, which provides autothrottle thrust control and flare guidance below 100 feet agl.

The E195 with the dual Collins HGS is certified to descend to a 50-foot decision height with 600-foot RVR. When rollout guidance is available and used, a 400-foot RVR at midfield is acceptable. The system can provide a 300-foot RVR takeoff capability with the low-visibility takeoff mode engaged, presenting ground-roll reference and guidance cues.

As we descended above the Columbia River, keeping the steering circle over the target circle satisfied the selected speed while correcting for a 10-knot left crosswind. At one mile, the runway symbol exactly overlaid the real runway ahead. At this point I thought, “I’ve never landed an airplane this big, where I’m sitting so high off the ground. Please, don’t let me slam it on or drop it in.”

The HGS wasn’t about to let that happen. At 100 feet agl a flare guidance cue appears below the aircraft symbol. At 50 feet the cue becomes a rifle scope-like circle with crosshairs. Keeping the aiming circle over the crosshair cue was all there was to it. As it came time to rotate, the crosshair cue began to rise and yoke back pressure easily kept the steering cue over it. Suddenly, the descent stopped, the throttles auto-retarded. Incredibly, this tyro jet pilot had made one of the five best landings of his life.

Bob Irish, principal program manager for Collins Flight Dynamics, noted afterward that the ease with which even a pilot totally unaccustomed to flying with HUD guidance can transition will be a boon to air carriers and operators of the larger corporate jets. The E170/175 and E190/195 jetliners will all have the same avionics and the 5600 HGS as standard or optional equipment, simplifying crew movement between the types in a given fleet, Irish noted.