Peter Henley/SEATTLE
Flying the stretched Boeing 767-400ER so soon after the Boeing 757-300 (Flight International, 26 February-6 March) offered intriguing opportunities for comparison. The two aircraft are similar in terms of procedures, handling characteristics and flight management. But one key advance in the cockpit could have a significant effect on pilots qualified to fly earlier Boeing types.
The narrowbody 757 and its widebody 767 sibling share almost total commonality. The change is to the flight instrument system. A relatively old-technology electronic flight instrument system (EFIS) made the 757-300 cockpit seem similar to earlier 757, but, unlike earlier 767s, the -400ER has a six-panel liquid crystal EFIS presentation that is nearly identical to the 777 and similar to the 747-400.
The 767-400ER is the latest Boeing derivative model to benefit from a comprehensive flightdeck revamp. As with the Next Generation 737, the 1980s technology incorporated in earlier models has been stripped out and replaced by 777 architecture. Unlike the 757-300 derivative, which retains its predecessor's cockpit configuration, the new 767-400ER has more in common with the 777 than with the 767-200/300 models from which it evolved.
To maintain fleet commonality, Boeing has studied the possibility of offering digital "round dial" primary flight information presentations on the -400ER, but the two launch customers (Delta Air Lines and Continental Airlines) have opted for modern tape type displays standard on the 747-400 and 777. While this may affect experienced airline pilots flying earlier Boeing types, increasingly, they will have to adapt to digital and tape presentations of latest EFIS displays.
The decision to adopt the latest display configurations makes it easier to incorporate future operational and safety enhancements. For example, little doubt remains about the value of the latest terrain awareness systems (TAWS) such as Honeywell's Enhanced Ground Proximity Warning (EGPWS). The 767-400 EFIS includes a compelling, large-format EGPWS display that would be difficult to incorporate in a "conventional" cockpit.
The 767-400ER flown by Flight International was the first of three development prototypes. This airframe (VQ001) had been used for all the flutter handling and performance trials leading to certification. The cabin was fitted with extensive test recording equipment and water ballast containers for weight and centre of gravity variations. Apart from three small recording cameras, a couple of g meters and several orange test switches, the cockpit represented a production aircraft. After completion of certification flying, it would be refitted for delivery to Delta Air Lines. The basic architecture of the cockpit - the control wheels, seats and overhead panels - remain classic Boeing. The large windows provide a broad field of view, but neither wingtips nor engines are visible.
The deep side windows open and slide rearwards to make a reassuringly large cockpit escape route and an escape rope is anchored in a small stowage over the window, in the cockpit roof. In typical Boeing fashion, the seats slide outwards at the limit of their rearward travel, widening the gap between seat and centre console and making the seats easy to enter and exit. The cockpit benefits from the widebody fuselage giving generous amounts of room outside each pilot's seat.
There is ample stowage for flight bags and a suite of pockets and receptacles are built into the side wall beside each pilot. Behind the first officer's right shoulder there is a fuse and switch panel, which seemed intrusive in an otherwise light and roomy cockpit.
Richard "Buzz" Nelson, chief 767 flight test pilot, took the right seat and I the left. The aircraft, parked on the ramp at Boeing Field, had ground power which allowed the six Collins EFIS displays to be powered. Each pilot's instrument panel houses two side-by-side 200 x 200mm (8 x 8in) active matrix liquid crystal displays, the outboard used for the primary flight display (PFD) and the inboard for the navigation display (ND). The central instrument panel houses the upper display, which shows the primary engine indicating and crew alerting system (EICAS) information, while the lower display, which lies horizontally at the forward end of the centre console, shows secondary EICAS information and systems synoptic pages. The pilots can switch displays from one display to another to compensate for a failure.
There is a flight management system control display unit (CDU) on the centre console next to each pilot's inside knee. Nelson used his to enter a simple flight plan to fly to and within an area of quiet airspace over central Washington state. The Honeywell 331-400b auxiliary power unit (APU), housed in the fuselage tailcone, was started via the APU control panel in the cockpit roof electrical panel. The APU may be started in flight and its power can be used throughout the flight envelope. Bleed air is available up to 17,500ft (5,300m). An EICAS display on the centre lower display showed the APU parameters during the start.
Next, the two General Electric CF6-80C2B8F turbofan engines, each rated at 63,300lb (282kN) of thrust, were started using bleed air from the APU. The engines had electronic engine control but no automatic start, or automatic start abort. The primary EICAS displays for the engines (in the centre upper display) comprised only two digital/analogue indicators - N1 (fan speed) and EGT (exhaust gas temperature). The indications were clear, crisp and unusually easy to read. This commendable paucity of primary indications left the display with plenty of space to display crew alert messages.
On the right side of this display there are equally brief and clear indications for flap position (in tape format) and undercarriage position. The undercarriage lever is in the customary Boeing position to the right of the centre instrument panel, where it comes easily to hand for the first officer and can be reached by the captain.
The lever gate has only two positions, up and down, and no neutral intermediate position. Secondary engine indications are on the lower centre display and comprise N2 rpm, fuel flow, oil pressure, temperature and quantity and engine vibration. The engine readings on both displays (ie primary and secondary) indicated left engine information to the left and right information to the right, minimising the risk of engine misidentification during abnormal or emergency engine handling procedures.
A difference in basic design philosophy between the 757 and 767 models involves the undercarriage and affects handling. The 757 was designed with stretch in mind and the undercarriage was originally long enough in the leg to provide tail clearance during rotation on the take-off and in the flare on landing in a future stretched development. The 757 is nevertheless sensitive to attitude in this respect, requiring the pilot to observe pitch limitations to avoid a tail strike.
The 767, conversely, could not be lengthened to its -400 form using the main undercarriage from the 767-200 and -300 models. Boeing has resolved this problem by lengthening the existing legs, and using the larger wheels, tyres and brake units from the 777. As a result, the mean height of the aircraft on the ground has risen by 460mm. No change was made to the nose leg length, so the 767-400 has a slight nose-down attitude. A pilot qualified in the -400 and an earlier-model 767 will probably notice a change in perspective arising from the slightly different eye position, but this is unlikely to affect his ability to transfer from one model to another.
As far as rotating and flaring the -400 is concerned, Nelson believes that a tail strike problem is unlikely. Pilots will need to be conscious of attitude and to exercise care - and the -400 is fitted with a tail skid similar to that on the 757-300, just in case.
Ease of taxiing
Taxiing the aircraft was a delight, despite its size. The carbon disc brakes were smooth and progressive. Although the nose wheel steering was low-geared, the long arm of the tiller was easy to use and direct in operation.
Small amounts of nose wheel deflection are controlled via the rudder pedals. When completing the pre-take-off checks, the tiller has to be held to prevent scrubbing of the nose wheel tyres. The full and correct movement of all the primary flying controls is ascertained through the system synoptic displayed on the centre lower display for the duration of the checks.
The 767-400 was extremely light for the flight. The all-up weight (AUW) was only 130,000kg (286,400lb) compared with the maximum permitted 204,570kg.
Acceleration was therefore brisk. Rotation required only a small rearward movement of the control column. Retraction of the undercarriage was audible in the cockpit but not intrusive. The 767-400 has a more powerful airdrive unit to retract the heavier undercarriage in the same time as the -300. Because of the aircraft's light weight, the mild temperature (17°C) and sea level field elevation, the rate of climb went "off the clock" to about 6,000ft/m (30.48m/s) during the initial climb to flap retraction at 1,000ft above ground level.
Like the 757, the 767 has well-harmonised primary flying controls. The roll control differs from the 757's in that each wing has two ailerons - one outboard and another between the inboard and outboard segments of the trailing-edge flaps. These inboard ailerons droop in conjunction with flap extension. The ailerons are augmented by six spoiler panels on the upper surfaces of both wings. The spoilers work asymmetrically to supplement roll control and symmetrically as airbrakes (speedbrakes).
The spoilers function after a few degrees of aileron deflection. The resulting roll control is powerful, with good artificial feel and light break-out forces. Roll acceleration and rate of roll are impressive. Smooth and progressive application of roll control by the pilot is required to avoid a "snap" response, but I found no tendency for pilot-induced oscillation as a result of lively roll control. Pitch control is via two elevators and pitch trim via the variable incidence tailplane (stabiliser), the position of which is controlled by dual trim switches on the control wheel, with alternative switches on the centre console.
Yaw control is provided by a single rudder. Two yaw dampers work through the rudder control system to improve directional stability.
The primary flying controls are powered hydraulically, with system redundancy but no manual reversion. If an elevator were to jam, pitch control would be preserved through the remaining elevator with less authority and higher forces. A control wheel jam would be countered through the other wheel after separation from the jammed control by the application of high wheel force by the pilot.
The 767-400 is stable, with good natural damping. During the climb, passing 20,000ft at 300kt (550km/h), a stick slap (pitch bump) to disturb the elevators produced dead beat or immediate damping. A rudder doublet, also at 300kt to provoke dutch roll, resulted in natural damping after about two cycles and immediately with the yaw dampers switched on.
The 767-400 wing is different from that on earlier 767 models and the 757 in that it has raked wingtips of composite construction to improve overall aerodynamic efficiency. Unlike upswept winglets, they lie flat in line with the mainspar. Boeing says they help to reduce take-off field length, increase climb performance and reduce fuel consumption. The wingtips are transparent to the pilot in terms of their effect on handling characteristics.
The 767-400's wing seemed well suited to high altitude. At 33,000ft (maximum cleared altitude 43,000ft), Mach 0.845 (normal cruise M0.80) and 127,000kg AUW, it was not possible to induce buffet with normal handling, either in level flight or in 45° banked turns. The handling remained crisp at this speed and level, although it must be emphasised that the aircraft was unrepresentatively light and 10,000ft below its maximum flight level.
We then descended to a block of airspace between 18,000ft and 20,000ft for two stalls. During the descent with the power at flight idle, passing 27,000ft at 300kt, the airbrakes were extended, which produced a slight pitch change and a little aerodynamic burble. The first stall was clean, the AUW 126,000kg and the power at flight idle. The speed was reduced, wings level, from the trim speed at 1kt/s. The stall was defined by strong natural buffet and there was no tendency to roll or slice. The controls remained effective at and near the stall and the stick shaker, activated almost at the same speed as the buffet, was assured.
Removing stall doubts
The same technique was used for the next stall with undercarriage down and flap 30. Again, clear natural buffet occurred, but the left wing dropped gently. The roll was easy to contain using rudder and roll control. During certification flying, the 767-400 had been found to be marginal in the "dirty" stall because of the tendency for one wing to stall just before the other. To remove any doubt about its handling in the stall, vortillons were fitted to regenerate spanwire flow at high angles of attack. Although the tendency to roll remains, it was gentle, controllable and safe.
At 10,000ft, with the AUW now 125,760kg, an engine failure was simulated at 1.23 Vs (stall speed for configuration) with flap 5 and full power. Nelson recommended controlling the aircraft with roll control only initially and then neutralising the roll control loads with rudder. This, he said, demonstrated how benign an engine failure was. He moved the left engine power lever to flight idle and I continued the climb at 145kt. It was easy to control the -400 with aileron and then feed in rudder. The resultant foot forces were light and easy to trim out using the electric rudder trim knob towards the rear of the centre console.
The next plan was a coupled (autopilot) simulated instrument approach and autoland at the Moses Lake, Washington, airfield. Runway 32R was in use, the weather was good, the airfield elevation about 1,200ft and the temperature on the ground 22°C. The AUW was by now 124,000kg. Number one autopilot was selected and a route planned to intercept the localiser at about 22km from touchdown. The requirements were easily entered via a CDU and the navigation display (ND) provided excellent situational awareness. Initially, the ND was in the map mode, in which the position of the -400 was represented by a triangular symbol at the centre, lower part of the display.
The way points were clearly displayed, together with the intended track. Useful and easy-to-assimilate digital readouts at the corners of the display included the frequency and distance measuring equipments of the two VORs selected, the distance to the next way point and the expected time of arrival, groundspeed, true airspeed and ambient wind. A wide choice of ranges ensured that a scale could be chosen that best visited the distance to go to destination or the next important way point.
Meanwhile, with auto throttle selected via the glareshield switch, the autopilot flew the aircraft smoothly and accurately in the speed mode via several altitude changes, eventually to capture the localiser. The PFD showed much information, but the display was clear and uncluttered. The flight modes appeared in panels across the top of the PFD, and airspeed and altitude were shown in vertical tapes either side of the display. Vertical speed, the top arc of a compass rose, the barometric pressure, instrument landing system (ILS) data, and (at low level) radio altitude were all shown logically and conveniently.
Before localiser capture, the ND mode was switched to APP (approach), which clearly showed the aircraft's position relative to the localiser and the runway. The pre-landing checks were completed before glideslope capture, including the selection of moderate auto-brake, and then, during the ILS approach, the number two engine was reduced to flight idle to simulate an engine failure. There was considerable thermal turbulence below about 2,000ft, but the autopilot coped with this and the engine power reduction smoothly and accurately. The autoland was smooth and competent, as was the automatic wheel brake application. I applied asymmetric reverse thrust and was easily able to keep the aircraft straight using the rudder pedal operation of the nose wheel steering.
The 767 was then reconfigured for visual circuits at Moses Lake. These included a simulated engine failure between V1 and rotate, which at such a low AUW was something of a non-event. As it was a development aircraft, we flew circuits to try the EGPWS in an actual closing track and altitude towards a mountain on the return flight to Boeing Field at Seattle.
Flight International evaluated EGPWS in the Aer Lingus Airbus A320 simulator. Now it was possible to compare that simulation with reality. At about 6,000ft and in excellent visual conditions, the 767 was flown directly towards a ridge, the top of which was about 7,000ft above sea level, starting from a range of about 15km and maintaining 230kt. Both map displays automatically changed to show a clear picture of the terrain ahead, with the mountain ridge in attention-grabbing red. At about 9km there was an audio warning from the EGPWS of terrain ahead and the aircraft was easily turned away to pass to the left of the high ground. This exercise served both to underline the safety improvement given by EGPWS and to confirm the faithful reproduction of the real thing in the A320 simulator.
The most important feature of the EGPWS was its early warning capability. It is triggered well before a standard GPWS or the radio altimeter would react and alert the crew in plenty of time to the danger, permitting a considered, almost leisurely, choice of escape route.
The 767-400ER excelled in most categories. It boasts the excellent handling qualities of its predecessors, but benefits from the change in cockpit philosophy, meaning it is now in step with technological advances.
Source: Flight International
