Flight Evaluation: Boeing 767-400ER
Air Line Pilot, February 2001, p. 22
By Capt. Terry L. Lutz (Northwest), Director, Aircraft Development and Evaluation Programs, ALPA Aircraft Design and Operation Group
The newest B-767 is not just a longer version of the original airplane. The truth is that the amount you can change the geometry of an airplane without making substantial changes to its overall configuration is limited. Boeing went right to the limit in some respects, added many cockpit features found in the B-777 family, and created the most refined addition yet to the Boeing product line.
FAA certification of the airplane was supposed to be wrapped up in early March 2000, but with the engineers’ strike at Boeing, the resulting backlog of flight test work meant that certification was delayed until early June. Three members of ALPA’s Aircraft Development and Evaluation Group—Capt. Ron Rogers (United), Capt. Joe Kohler (Northwest), and I—had the opportunity to fly the B-767-400ER on June 5.
From the beginning, we focused on how the changes made to this model of the B-767 affect the way that pilots fly the airplane on the line. This is a subtle change from the way we approached aircraft evaluations in the past, when our focus was mainly on performance and handling qualities.
Seen from the second-floor engineering offices along the flight line at Boeing Field, this airplane appears to have a rakish nose-down appearance. That’s the first clue of the many changes Boeing made when it lengthened the airframe.
This is the second stretch of the original B-767. The first stretch was made in 1988 when the B-767-300 was introduced, and the current version is stretched an additional 21 feet. An 11-foot section has been added ahead of the wing, and a 10-foot section added behind the wing.
With the longer airframe, ground clearance becomes a consideration. If the airplane were limited by its geometry, it would require both higher takeoff speeds and higher landing speeds to avoid tail strikes. So Boeing made the main landing gear struts 18 inches longer and moved them outboard so the gear would still tuck into the wells. This gives the airplane a 1-degree nose-down rake while sitting on the ground. It looks like it wants to spring into the air, right from where it sits.
Tail clearance of the -400ER is the same as the tail clearance of the B-767-300. While tail strikes are not expected to be an issue, rotating 10 knots early or touching down 10 knots too slow will touch the tail. The airplane has a tail skid with a crushable cartridge, but it has no cockpit light that indicates to the pilot that the cartridge has been crushed, as the B-757-300 has. The pilots who fly the B-767-300 have reported few tail strikes, and Boeing expects that the –400ER will have about the same low rate of strikes in service.
We briefed for the flight with Capt. Buzz Nelson, B-767 chief test pilot (see Pilot Profile, sidebar), and Lead Flight Test Engineer Henry Stahl. Having worked together on the –400ER development program from day one, they filled us in on the important differences in this model, including some interesting and significant changes on the flight deck. The evaluation profile we briefed included departure and climb from Boeing Field, an eastbound cruise leg to a working area northwest of Moses Lake, Wash., landing transitions at Moses Lake, and a systems review on the return leg to Boeing Field.
Walk-around inspection revealed some interesting aerodynamic changes. First are the raked wingtips (see photo). Boeing considered installing winglets on this model, but found several competing considerations. The objective was to recover the performance lost by increasing the maximum gross weight of the airplane. Increasing the wing area (gaining lift) would enhance takeoff and climb performance, while decreasing drag (using winglets) would recover performance over a long period of time at cruise.
The existing wing could not support the loads that winglets would impose, so Boeing chose the raked wingtip design. Set at 57 degrees of sweep, the raked wingtips add 7 feet 8 inches to each wing and account for 74 square feet, or 2.4 percent, of the total wing area. The raked wingtips reduce balanced field length, make possible a higher initial cruise altitude, and still reduce fuel burn by 1 percent versus the basic wing design. Now, if the world’s tallest catering truck manages to wrinkle one of your wingtip extensions, you can still operate by removing both wingtips. They are designed to be removed easily, and the flight can continue to a repair destination with the wingtips MEL’d.
Another interesting aerodynamic change from earlier modes of the B-767 is the addition of three vortilons under the leading edge of the outboard slats. During stall testing, Boeing found that stick forces were getting light near the stall, and that uncommanded roll at the stall would produce up to a 20-degree bank. Both characteristics were within certification tolerance, but with the addition of the vortilons, the flow separation problem near the stall was eliminated. Vortilons, found on aircraft from the LongEze homebuilt to the EMB-135/145, and now the B-767-400ER, can energize the airflow just enough to eliminate a potential problem.
The nose landing gear of the -400ER is unchanged from earlier models of the B-767, but the main landing gear are completely new. The new airplane’s wheels, tires, and brakes are from the B-777, but the brake control system is the same as on earlier B-767s. Boeing has retuned the antiskid/autobrake software to reflect the characteristics of B-777 brakes. The hydraulic control modules and alternate extend power pack are also from the B-777. This provides some commonality for airlines that operate both airplanes.
The flight deck of this airplane is designed with six Collins 8- by 8-inch LED displays from the B-777. They are the brightest, most distinct displays I have seen on any airliner flight deck. Their software is programmable, which allows operators to select display arrangements compatible with other aircraft in their fleet, reducing the training required to transition between airplanes. This airplane, for example, had an angle-of-attack display in the upper right portion of the PFD. When flaps are extended, the display indicates optimum AOA with a small green band. With flaps retracted, a line shows the AOA for stickshaker activation.
The center EICAS display shows engine parameters and can also be used as a "hot spare" for any of the other five displays. The lower EICAS display in the center can depict only the status of the landing gear and flight controls, but has the growth capability to depict all the systems currently displayed in the B-777, along with an electronic checklist. The ALPA team felt that this upgrade is needed now to provide pilots with an accurate synopsis of current system status. The appropriate system page should be displayed automatically with a failure, along with the appropriate checklist. This method improves flight crew knowledge of systems and reduces errors while the flight crew accomplishes abnormal procedures.
Boeing has put a lot of emphasis on upgrading the cockpit, but not so much that pilots currently type-rated in the B-757/B-767 won’t be able to transition to this model with 3–4 days of training. The ALPA team felt that, with a few more changes to the cockpit, the B-767-400ER might strongly resemble the B-777. Without considering systems differences, particularly the FBW system in the B-777 and with current Advanced Qualification Training Programs (AQP) used by many airlines, cross training between the two types of airplanes could be straightforward for the pilots and beneficial for their airlines.
Systems on the B-767-400ER are robust and designed with the redundancy required of an airplane that is certified to 180-minute ETOPS. All three generators are 120 KVA, and the APU is capable of a cold start at cruise altitude. The airplane is equipped with a ram-air turbine (RAT), which provides emergency hydraulic power only. The air-cycle machines are from the B-777, and flight attendants can control the cabin temperature of the B-767-400ER from the cabin. The flight crew sets the position of the trim air valve, and the flight attendants can move it warmer or colder from that initial position. The engine antiice system is automatic, triggered by a Rosemont probe that measures moisture counts, or little bits of ice that fall, and turns the system on at a threshold value.
Numerous cockpit design features of the B-767-400ER are intuitive and make the cockpit a pleasant work environment. For example, minimums bugs are selectable to the exact foot, so you don’t have to round up the numbers on the Jepp chart. The knob to select minimums moves in hundreds of feet if you move it fast, and in 1-foot increments if you move it slowly—very intuitive. The 3 VHF radios are tuned with just one display, but you select which radio—left, center, or right—to tune. And, a remote button for the boom mike is up on the glare shield, so you can talk and keep a visual focus outside the airplane, if necessary. The new airplane’s sunshades are very well designed, with a clip-on style for the center windscreen and a rolling screen that moves forward to cover the sliding window, and one that moves aft to cover the aft side window.
Starting the 63,500-pound–thrust General Electric CF6-80C2 engines is a two-step process. The pilot selects start on the overhead panel and places the fuel switch to run when the engine reaches 20 percent. This is different from the single-step process used on the B-777 and other aircraft, to retain commonality with existing models of the B-757/767. A red light inside the fuel switch, which illuminates when a fire is detected, makes determining which engine to shut down very straightforward.
Peak EGT during start was 420 degrees for the right engine and 451 degrees for the left engine. The new airplane’s generators come on line with a "no power break" feature, meaning that no loud "snap" occurs when the generators come on line, and the cockpit displays are unaffected by the power transfer.
Before taxiing, flight controls are checked using the flight control page on the center display. Bank angle marks are on the top of the yoke. We found that the 6.0 mark represented about one-half deflection, which we would refer to later in the flight.
The airplane was parked in the No. 1 spot on the Boeing ramp, pointing away from the runway. I had to pull forward, check brakes, start an immediate 90-degree turn, and then use minimum power while taxiing uphill to avoid putting jet blast into an open hangar and onto Delta’s first B-767-400ER, which was being prepped for delivery. The nose gear is behind the cockpit, so the pilot has to compensate for both the length of the airplane and the location of the nose gear. The tiller required about 180 degrees of deflection to turn out of parking.
I would rate the brakes on this airplane as excellent. We taxied with a zero fuel weight of 235,400 pounds with 65,100 pounds of fuel, for a gross weight of 300,500 pounds. This is considerably less than the max gross takeoff weight of 450,000 pounds. At this comparatively light weight, you would expect the brakes to be a bit sensitive. Instead, they were smooth and symmetric. Precise steering and excellent brakes made taxiing in tight quarters an accurately controlled nonevent.
We planned the takeoff for flaps 15, with V speeds of 129/136/146. After we initially set power for takeoff, autothrust brought the thrust up to 109.7 percent N1. Capt. Nelson briefed that the nose would feel light on takeoff, but I couldn’t keep my "Douglas hands" from making a segmented rotation.
We stabilized in the climb at V2+15 and began cleanup at 1,000 feet AGL. Cleanup was straightforward, with no noticeable pitch changes with gear and flap retraction. After accelerating to 250 knots, our climb rate was 5,300 feet per minute at 99.1 percent N1 and 17,000 pounds per hour fuel flow. After passing 10,000 feet, we turned east and accelerated to 340 knots for the climb to FL290. From brake release, the climb had taken just 12 minutes. The noise attenuation work Boeing has done in the cockpit resulted in a quiet, comfortable environment.
As we continued east toward a working area near Moses Lake, I performed some basic checks on handling qualities and found that the forces, displacements, and aircraft response were exceptionally well balanced in all axes. These excellent handling qualities have become a Boeing trademark. The B-767-400ER handles slightly better than the B-777.
With the absence of the "soft protections" incorporated in the B-777, the B-767-400ER feels more "like an airplane." Sharp control inputs in the B-767-400ER do not produce as much aeroelastic response as in the B-777, particularly in the roll axis. As Capt. Kohler so clearly stated after the flight, "This is the first widebody aircraft I have flown that didn’t have that widebody feel." Translation: "This is the best handling widebody airplane in the Boeing product line." Capt. Rogers and I both agreed.
As I mentioned earlier, our objective was to bring a line pilot’s perspective to the evaluation. So our first maneuver east of the mountains was a rapid descent, simulating loss of cabin pressure. To make this more interesting, and because it is standard procedure at some airlines, I flew the maneuver completely on the autopilot. I dialed the altitude from FL290 down to 11,000 feet, disconnected autothrust and brought the throttles to idle, dialed the speed up to 350 knots, and deployed the speedbrakes.
On the initial pitchover, the rate of descent increased to 9,600 feet per minute at 7½ degrees nose down, then slowed to 5,300 feet per minute as the airspeed stabilized at 353 knots. The time from start of the descent to level-off at 11,000 feet was just 3 minutes. Very impressive, particularly since we flew the maneuver by interfacing with automation, rather than manually.
We entered an arbitrary working area into the Honeywell Pegasus FMC and set up for some flight maneuvers northwest of Moses Lake. The first was a check of roll rate in bank-to-bank rolls from 30 degrees to 30 degrees at ½ wheel deflection. Flying the clean airplane at 350 knots, bank-to-bank took 4 seconds, for a roll rate of 15 degrees per second. Here is where a sharp control input initiated an aeroelastic response from the airframe. A later check of this same maneuver with flaps 30 at Vref=136 gave a bank-to-bank time of 6 seconds, or a roll rate of 10 degrees per second. This excellent response at slow speed in the landing configuration is another indication of the exceptional handling qualities of this airplane.
I set up for some clean stalls at a weight of 290,100 pounds. Using a 1-knot-per-second deceleration in level flight at 11,000 feet, 15 to 25 pounds of force were gradually required to bring the nose up to 10 degrees nose high, where light buffet occurred just before stickshaker activation at 166 knots. Recovery was very predictable with power application and was accomplished without losing altitude. No pitch-up was noticeable with power application, which is prevalent with underwing-mounted high-bypass engines.
Although we did not take the airplane to full stalls, the B-767-400ER incorporates a yaw damper stabilizer module (YSM), which provides yaw damping, rudder ratio, and elevator feel shift. The YSM provides feel shift at the yoke as the airplane approaches stall with an aft cg. Feel shift occurs at CL max and can run the elevator forces up to about 50 pounds at the stall.
We then set up for landing configuration stalls with flaps 30 and a Vref of 136 knots. We performed the approach to stall in a 20-degree banked turn, and the stickshaker came on when pitch reached the pitch limit indicator, at 113 knots. We recovered with full power with minimal altitude loss.
Before we cleaned up the airplane, Capt. Nelson talked me through a "tameness demo" that Boeing likes to conduct. Slowing to 147 knots, I applied full power to both engines, then Capt. Nelson pulled one throttle to idle. Climbing at a V2 of 156 knots, I maintained heading with aileron control alone. With the airplane slowly climbing and accelerating, I was able to make turns to headings with aileron only. Wheel deflection was approximately 6 units, or one-half of available deflection. Feeding in rudder to center the wheel at 156 knots took approximately one-half rudder deflection, and when the rudder was fully trimmed, 4 units were displayed on the rudder trim indicator. Except for the performance loss with ailerons and spoilers deflected, this demonstrates the control reserve available at V2 with one engine operating at full thrust and the other at idle.
Two related issues emerge, however. First, for the same maneuver, how much performance reserve would the pilot have on one engine at MGTOW? Second, we felt that the thrust asymmetry compensation (TAC) feature in the B-777 eliminates the problem of performance loss after engine failure. With TAC, the airplane senses the loss of thrust on one engine and automatically applies the proper rudder input to minimize performance loss. TAC provides for the flight control system what moving autothrottles provide for engine thrust: automatic control, tactile cueing, and pilot override with light force application.
Capt. Rogers jumped into the left seat and warmed up with some steep turns. At 250 knots, the airplane is very speed stable, meaning that the pilot can set trim and power easily, and it stays there. Speed control, another aspect of handling qualities, is very apparent in the B-767-400ER.
We then descended into the Moses Lake landing pattern, feeling right at home in the traffic pattern with B-747s, L-1011s, and C-17s. Groundspeed in the pattern is nicely shown in the upper left corner of the nav display.
Flying final with a Vref of 143 knots, Capt. Roger’s first landing was with autobrakes 1. Approaching preset minimums, the airplane annunciated height above touchdown in 10-foot increments (40-30-20-10). Brakes 1 was a very smooth setting. Brake application was almost imperceptible at initiation but gave a smooth normal stop. Approximately one-half to three-quarters tiller deflection was required for the turn off the runway.
After waiting for traffic to clear, Capt. Rogers made a normal takeoff, and Capt. Nelson pulled the left engine to idle at V1. As noted during the safety demo, approximately one-half rudder deflection was required during the initial climb, and both heading and bank angle were easily controlled. The airplane is predictable and controllable with a simulated engine failure at V1, which is significant when it occurs on your first takeoff in the airplane, as it did for Capt. Rogers. Completing a 90/270 turn back to the runway, he flew a single-engine approach with flaps 20 and a Vref of 157. Reconfiguring the airplane after touchdown, Capt. Rogers made a normal takeoff, and I again took the left seat.
My first landing was set up to demonstrate the autoland capabilities of the airplane. On initial flap selection, we selected speed mode on the autothrust controls. We flew the approach with flaps 30, and the approach appeared normal until we were on short final. The airplane appeared to trend a little low at that point, and in the flare it began to float at the 10-foot callout. Capt. Nelson was a little uncomfortable with that and disconnected the autopilot just at touchdown. We reconfigured and made a normal takeoff.
The Boeing engineers on board recorded the entire approach and, about a week later, let me know what they had found. From 300 feet to 150 feet, we had had a tailwind shear of 1 knot per second, then from 115 feet to 25 feet the shear increased to 1.5 knots per second. From about 25 feet AGL to 4 feet AGL, the tailwind sheared from 14 knots to 2 knots. The autothrust system kept the power back on final to stay on the glideslope, then had to add power as the tailwind sheared to near zero. This change in power occurred just as the airplane was beginning to flare, and the few knots of extra airspeed caused the float at the 10-foot callout. With the autopilot latched to the glideslope, the sink rate at touchdown was 270 feet per minute. Working right at its operational limits, the autoland system performed exactly as designed.
On the go from the autoland, we left flaps at 5 degrees and set up for another visual pattern. With flaps 30 and Vref=142 knots, I made a normal landing. The pitch change required to flare this airplane is 2–3 degrees, and the nose attitude is fairly flat, giving excellent visibility throughout the flare. Derotation to put the nosewheel on the runway was very predictable, although you do have to pitch down another 1 degree below level flight. While the flare callouts help, height above the runway is relatively easy to judge. On the go-around from this touch-and-go, the nose felt slightly light, then slightly heavy as the flaps were retracted from 25 to 5 degrees. When the flaps were retracted from flaps 1 to zero, the nose pitched down slightly, then came right back up without retrimming as the airplane accelerated.
During the initial climb back to Boeing Field, Capt. Kohler took the left seat, and while he flew, Capt. Nelson and I worked through some basic emergency procedures. First, we simulated generator failure by de-selecting the left generator. Until the APU generator is selected on, the utility bus and galley bus are automatically shed. As during start, no generator hard break occurs as generators go on or off line. The emergency procedure is to cycle the generator one time, and if it is not recovered, use the APU generator.
We simulated hydraulic failure by shutting off the right engine hydraulic pump. This really has no effect on the system, or on the configuration for landing. With two electric hydraulic pumps and a RAT for hydraulic power, the airplane has plenty of hydraulic system redundancy. Using checklist procedures, I found that with right hydraulic pump failure, the only items lost are the right autopilot and the autobrakes.
Capt. Kohler flew the Jaksn Arrival to Boeing Field. During descent, he noted that very little pitch change occurred with the speed brakes extended (a good thing), but no light or similar indication showed that the speed brakes were extended. If you leave the speed brakes deployed and thrust increases to more than 70 percent N1, a "Speed Brakes Extended" message comes up on the EICAS, and a caution beeper will sound until the speed brakes are stowed. During landing approach, with flaps set at 25 or 40 degrees, or while at 800 feet or below, a warning will sound if the speed brakes are extended. And, if the pilot selects go-around thrust, the speed brakes will automatically retract.
Setting up for our final landing, Capt. Kohler manually extended the landing gear. A display appears on the EICAS for the tailskid (which stays up) and the gear doors (which remain down). For this approach, we weighed 273,500 pounds, with 36,900 pounds of fuel on board. We flew final at Vref=137, with flaps 30. Autobrakes 4, which we selected for landing, gave a firm, solid stop, but was by no means extreme or disconcerting. This setting would be appropriate to use for landings on short, wet runways.
We shut down abeam the same No. 1 parking spot, 2 hours 20 minutes after we taxied out. This probably is the best overall airplane in the Boeing product line, but not just because of the way it flies. Truth be told, as pilots, we have far too few chances to actually hand-fly the airplane. With the B-767-400ER, we found that our interface with airplane systems, autopilot, and autothrust were equally as good as our interface with the manual flight controls. The roll-out sunshades, pen holders, conveniently located push-to-talk buttons, good lighting, and excellent noise attenuation will make a big difference to those of us who regularly use the airplane.
Designing a new derivative of an existing airplane creates some challenges so that it is certified with a common type rating with the models that preceded it. While in general this reduces training costs and makes transition to the new model easier for pilots, it clearly restricts innovation.
We gave this airplane high marks in almost every category, but common type rating issues kept Boeing from including all systems pages on the EICAS and an electronic checklist. Both are the industry standard in other fleets.
Also, a major safety consideration on takeoff with any heavy twin-engine aircraft is dealing with engine failure. The TAC system used in the B-777 provides a significant safety improvement, but if used in the B-767-400ER, would the type rating still be considered "common"? These are a few examples that tell us that the line between refinement and innovation is being drawn by a "common" No. 2 pencil. The B-767-400ER is the most refined airplane in the Boeing product line, but innovation is necessary to truly raise the industry standard.
The B-767-400ER has less range than earlier versions of the airplane. Why would anyone want to build a new airplane with less range than the previous one? Don’t we want each successive model to be better than the one before? Let’s take a quick look at what is really going on in terms of range.
Intuitively, we think, "Hmmm, let’s see, we have a longer, heavier jet with bigger engines; both changes mean a higher fuel burn, so we have less range as a result." But what’s the real relationship here? The formula for aircraft range is generally associated with a Frenchman named Breguet. For turbojet aircraft, the Breguet Range Equation is
The first term represents the characteristics of the engines, where c is specific fuel consumption. To keep c as small as possible, the engines must be operated at an rpm and airspeed that optimize their efficiency. The second term is the lift-to-drag ratio. For maximum range at constant altitude, this term is maximized when the airplane is flown at an angle of attack at which parasite drag equals three times induced drag. The pilot is never going to know when this relationship is satisfied, so we fly at the speed the book tells us.
The thing we can really understand is the last term, the weight fraction. If we could fly with all of our payload as fuel, the range of the airplane would be at its maximum. But we have to carry people and cargo to make our airlines profitable. With a bigger airplane and more payload, but with the same fuel capacity, the weight fraction is smaller, so range is reduced. That is the technical reason that your intuition is correct!
To recover the range lost by stretching the airframe, Boeing will try to add fuel capacity to future models. Fuel could be added in the vertical fin or horizontal tail. It could also be added in the cargo bays, but that would reduce the payload capability of the airplane. These are typical design tradeoffs; a magic solution for increasing aircraft range does not exist.
Meet The Test Pilot
A native of Seattle, Capt. Buzz Nelson went to Alaska after earning an engineering degree at the University of Washington. He worked as a bush pilot and flew for the Naval Arctic Research Lab. In 1973, having never flown a jet, he went to work at Boeing as copilot on pre-delivery flights on Boeing 707s, 727s, and 737s.
Capt. Nelson has been involved in development and certification programs for the Boeing 737-200/300/400, 747-400, 757-200/300, 767-200/300, and 777-200/300. He also served as chief research pilot, supporting such programs as the B-7J7, and for nearly 10 years was a member of the SAE S-7 Committee, which writes design criteria for handling qualities and flight deck design of large transports. He is currently chief pilot for the B-767 program, a position he has held since 1991. He is responsible for all engineering flight test activities related to the Boeing 767 model airplane, including its newest derivative, the B-767-400ER.
During his 40-year aviation career, Capt. Nelson has flown more than 14,000 hours and is qualified on all current models of the Boeing 737, 747, 757, 767, and 777, as well as several out-of-production and vintage airplanes. He currently lives in Seattle and owns both a Christen Eagle and a float-equipped Cessna 180. He enjoys flying vintage airplanes and has been actively involved with a number of restoration projects, including the Boeing 247, 307, and B-17, the airplane that his father worked on at Boeing as chief project engineer.