Air Line Pilot, March 2000, page
By Capt. Ron Rogers (United),
Director, ALPA Aircraft Development and Evaluation Programs
I recently had the privilege of flying two Boeing transport aircraft that do not need hydraulic power to operate the primary flight controls. One was the B-247, which was built in 1933, operated by United Airlines, and now owned by the Museum of Flight in Seattle. The other was the Boeing B-717-200. Previously known as a McDonnell Douglas MD-95, this aircraft became the Boeing B-717 by "marriage." In this age of irreversible, hydraulic, fly-by-wire flight controls, I am sure that a number of pilots still appreciate what can be considered a pure, reliable, and simple aircraft flight control design.
Capt. Terry Lutz (Northwest), First Officer Dave Hayes (Northwest), and I conducted the B-717-200 flight evaluation. Capt. Lutz flies DC-9s and is a long-time member and vice-chairman of ALPA's Airworthiness, Performance, Evaluation, and Certification Committee with an extensive test and evaluation background. F/O Hayes also flies DC-9s and is a former Navy test pilot who is still involved with some fighter test flying on the side.
Although capable of much greater range, the B-717-200 is Boeing's answer to the market need for a short-range (400 nm) 100-passenger aircraft. The basic range of the B-717 is 1,370 nm, with an extended range option of up to 1,810 nm. The B-717-200 is the base aircraft with the potential for family members having 20 fewer seats (B-717-100X) and 20 more seats (B-717-300X). The marketplace will dictate the introduction of these derivatives of the base aircraft.
This aircraft has some very interesting design features. In some respects, the design of this highly derivative aircraft complies with ALPA design policies better than many new aircraft.
The B-717 traces its roots back to the DC-9s of the 1960s. In fact, the B-717 can be considered an updated version of the DC-9-34. The two aircraft share the same type rating. The FAA-approved transition course for the B-717 requires 11 training days for a DC-9/MD-80 (analog) pilot to complete training, 9 training days for an MD-88/MD-90 (EFIS/FMS) pilot, and 24 training days for an initial qualification.
The B-717-200, designed to seat 106 passengers in a two-class configuration, has the following design weights for baseline/(optional) configurations:
* maximum takeoff gross weight, 114,000/(121,000) pounds;
* maximum landing weight, 102,000/ (110,000) pounds;
* maximum zero fuel weight, 96,000/(100,500) pounds; and
* maximum fuel quantity, 24,600/(29,500) pounds.
The B-717's maximum certified altitude is FL370. Operators who use the aircraft in the 400-nm or less range will typically operate at cruise altitudes of FL250 to FL270.
Economy and efficiency
The B-717 does what it was designed to do--operate economically and efficiently in the short-haul market. The airplane's systems are sufficiently simple and straightforward for reliable high-frequency operations. The avionics are sufficiently sophisticated to allow for efficient flight operations. The B-717 exhibits the good handling qualities of the DC-9 series of aircraft.
If you want more bells and whistles, buy the Airbus A318, which has commonality advantages for an operator who also owns A319s, A320s, or A321s. The A318, however, because it is a twice-shortened version of the A320, is more expensive to purchase than the B-717, has an extra 17,000 pounds, and therefore will be more expensive to operate on short-haul routes.
The B-717, interestingly enough, is a much-improved version of the previously proposed MD-95.
Initially, Boeing offered two versions of the MD-95 flight deck. The first was simply a continuation of the MD-80/88/90 design. The second had a significant avionics upgrade, called the advanced flight deck (AFD), resembling the MD-11 avionics suite.
The B-717 is now offered only in the AFD configuration, which was expensive to develop. But for the B-717 to stay competitive in the marketplace, Boeing really had no option but to make the AFD improvement. The previous MD-88s and -90s suffered from the problems of derivative aircraft--an old design is continued because of the expense of redesigning an aircraft or its systems. But you can stretch the string only so far. The AFD can support CAT IIIb and FANS.
The B-717 will be certified to Federal Aviation Regulation Part 25 up to Amendment 82 and the European Joint Aviation Regulation 25 up to Change 14. Boeing got eight exemptions to the regulations, six equivalent safety findings, and five special conditions.
We reviewed the requested exemptions to the FARs and JARs and did not discover any significant shortcomings. FAA/JAA certification was expected in September. The B-717, in spite of its derivative nature, complies very well with the FARs.
First, let's look at some of the interesting design aspects of this aircraft. Losing all hydraulics is not a problem--the aircraft is essentially flown manually.
Get into a problem and want all available engine thrust? Push through the break bar, and you get the maximum thrust that the engine is capable of safely producing. The airlines' bean counters imposed no artificial thrust limits.
The autothrottle system provides low-speed and high-speed protection features and automatic thrust advancement for windshear encounter or engine failure. The autothrottle system will automatically engage to help avoid exceeding maximum or minimum speeds. For example, if you get too slow, the power comes in; if you get too fast, the power comes back. The autothrottles move, and if you don't like the response of the system, you can simply override the throttles' movement.
Manual override of the automatic flight controls and autothrottles is always available. The flight control panel uses speed, heading, and altitude knobs that operate similarly but have different shapes and a very positive tactile feel.
The main instrument panel on the B-717 contains a six-across arrangement of 8- by 8-inch liquid crystal displays. The captain's three LCD displays and the standby instruments can operate for 96 minutes on battery power alone!
The overhead panel has been redesigned to present a more logical system layout than that of the MD-80/88/90 series, although the systems do not function interactively as in the MD-11. That is, for an engine failure, the systems are not automatically reconfigured to maintain fuel balance or ensure pneumatic pressurization. The pilot must perform these actions manually.
All of the lighting switches have been moved to the front of the overhead panel for easy access and activation. The thunderstorm light switch, however, did not "move" well. Because of its former rear location, the switch was designed with a large bat shape to allow for easy tactile recognition and activation. This same switch design has been retained in the "move" and now represents a crew injury hazard because of its shape and location.
The suitcase handles that were used for trimming the elevator have been eliminated. Their design dated back to the DC-8, and an electrical switch has replaced them.
The speed brake handle no longer is limited to one-quarter increments. The speed brakes may be selected to any intermediate value, and they will stay in the selected position. If thrust is applied while the speed brakes are extended, they will automatically retract. The handle stays in the selected position and must be moved to the stowed position to reset the system. Ideally, the handle should always indicate the actual position of the speed brakes.
We were concerned that the pilot might not be able to simultaneously select high power and speed brakes if, for example, an immediate return to the airport is required and the landing weight must be reduced. We found this not to be a problem because the speed brakes will retract only for thrust levels above maximum continuous thrust.
The flap system is a double-slotted design and uses the standard (DC-9) dial-a-flap system to permit selecting an optimum flap setting. Two-position leading edge slats and flaps are provided.
A few problems, such as needing a mirror to read the magnetic compass, were held over from the previous DC/MD design, however. We were surprised that a redesign of the magnetic compass did not accompany the other aircraft improvements.
Many other items have been improved. The flap handle has been changed into a single activating unit, not the previous split-slat/flap-handle design. A gear warning horn will sound only when it is really necessary (210 KIAS or slower below 1,200 feet AGL), instead of being a continual annoyance. Flight crews will greatly appreciate this improvement.
The original design of the fuel shut-off switches had a positive mechanical lock--a button had to be depressed to release the switch. The current design does have a lever-locking design, but it should also have a fence to protect the switches, or some other method of achieving a more positive mechanical lock. We are concerned that the switch could be inadvertently bent, broken, or activated as a crewmember gets into or out of the seat.
A provision for securing the crew's luggage is needed. The strap-and-latch system on the MD-80 is not a good choice to emulate. This design does not work well because the tie-down strap is difficult to access because of the cockpit layout. The latch design is also inadequate and needs to be improved.
The integral drive generators cannot be manually disengaged--they will only disconnect, and this is done automatically, for thermal exceedances.
Enhanced GPWS is the baseline. We have been very encouraged to see that a growing number of manufacturers do not consider this advanced and very important safety system to be an option. You buy the aircraft and you get EGPWS--Boeing doesn't even give the bean counters the option to save a few pennies at the expense of one of the best enhancements to flight safety available.
The B-717 will also come with a predictive windshear warning system, dual GPS, and a digital flight recorder capable of recording 500 individual flight parameters.
We found a problem with the circuit breakers behind the captain's seat. They can be easily damaged, and the installed guard does not appear to offer adequate protection.
The crew oxygen masks are the desired full-face Aeros brand, with the integrated smoke goggles. This type of integrated smoke goggle/oxygen mask represents a quantum improvement over the previous design of separate goggles and masks.
The B-717 has two independent 3,000-psi hydraulic systems, with no fluid interconnection. Hydraulics primarily power the landing gear, the slats and flaps, and the rudder.
The B-717's advanced flight deck configuration was expensive to develop but needed to keep the aircraft competitive in the marketplace.
The elevator control system is primarily a manually operated system with dual cables operating control tabs. Two independent elevator surfaces are provided, each having a control tab and a geared tab. The stabilizer is trimmed by primary and alternate electric motors. Elevator hydraulic boost is provided when the pilot commands more elevator trailing edge down than is achieved with just the manual tab. This usually comes into play only during a stall recovery. Aural and visual indications are provided for stall warning along with a stick pusher (the JAA requires a stick pusher for a T-tail airplane). The engine nacelle strakes and the engine pylon design provide deep stall protection, ensuring that the aircraft will recover if it attains extreme angles of attack If the aircraft is stretched, nose strakes may also become necessary.
The rudder control system consists of a single cable to a single power-control actuator. With the system powered, the control tab is locked to the rudder surface. Loss of hydraulic pressure will cause the system to revert to manual operation.
The aileron control system consists of a cable-driven control tab for each aileron. If one of the cables jams, the control system can be split. Each aileron also contains an electrically driven trim tab. The roll spoilers (two per wing) are electronically controlled, hydraulically actuated, and integrated with the ailerons to provide additional lateral control. This spoiler design is much better than the original, rather complex, DC-9 mechanical linkage. The fly-by-wire spoiler operation was much smoother for lateral control than the mechanical system found on the DC-9.
Engine thrust is normally limited to 18,500/(21,000) pounds per engine. By pressing through the break bar, engine thrust can safely be increased to 25,000 pounds or more, depending upon N1 and EGT FADEC-controlled limits. If the throttles are pushed through the break bar before rotation, some Vmc considerations may arise Above V2+10, the airplane should not have any controllability issues.
The two Rolls-Royce BR-715 turbofan engines have proven to be very reliable in flight tests. The engines were quite noisy on startup, however. We were told that the fuel metering will be changed to alleviate this problem.
The forward galley door is not designed to allow quick servicing, which should be of primary interest for a short-range, multihop aircraft. The galley door is only high enough to allow a cart to pass. The individual servicing the galley must push the cart ahead and then follow it through the door. This is not a user-friendly design.
The B-717 has a capable anti-ice system that includes, as all such systems should, the leading edges of the horizontal and vertical stabilizers. The system operates full time, with no cycling between the wings and tail for anti-ice air.
A full class "C" cargo compartment fire-suppression system is installed.
The aircraft had a few early brake system problems, including a 220-Hertz squeal that Boeing corrected by changing the brake lining. Because of the short-range/high-cycle type of flying that this aircraft will perform, Boeing preferred steel brakes--they cost less than carbon brakes, which are lighter and are preferred for longer-range aircraft that make comparatively fewer landings. Brake temperatures are displayed, but tire pressure is not, even as an option. Full-time tire pressure monitoring, although an option often removed (not by pilots), can be very effective in preventing a high-speed abort for a tire failure because of low tire pressure--a fully preventable event, if only the flight crew is given the proper information.
The test flight
Our flight evaluation was conducted out of Boeing's Yuma, Ariz., flight test facility. Capt. Ralph Luczak, the B-717-project pilot, occupied the right seat, and I took the left. I must admit that the flight deck has a much-improved appearance over the earlier MD series of aircraft. A few items were still not quite right, such as having the autobrake selector switch on the overhead panel. Overall, however, I found the aircraft more user friendly than the pilot's seat.
The flight test members at Boeing's Yuma, Ariz., flight test facility. From left, Tom Melody (Boeing), Capt. Terry Lutz (Northwest), Ralph Luzak, Boeing's B-717 project pilot, F/O Dave Hayes (Northwest), and Capt. Ron Rogers (United).
I programmed the FMS and found the speedbrake handle to be somewhat in the way. I entered the zero fuel weight of 76,300 pounds, and the FMS automatically entered the fuel and calculated a takeoff gross weight. For our gross weight of 101,000 pounds, we had a V1=118, Vr=129, and V2=136 for a takeoff flap setting of 13 degrees--the normal takeoff setting. The normal landing setting is 40 degrees. In the next FMS upgrade, the V speeds will be calculated automatically once the zero fuel weight is entered. For our weight and a temperature of 63 degrees F, our balanced field length was 5,253 feet.
The engine start was straightforward, and the engine FADECs fully protects it. To start the engines, the pilot must manually turn off the packs. The pilot pulls out the start knob and selects the start switch to auto. The engine start was rapid with a turbine gas temperature (TGT) peak of 593 degrees C; the start limit is 700 degrees C. The start knob automatically pops out at 40 percent N2. The engine idled at 22 percent N1 with a fuel flow of 710 pounds per hour. Once the engines are started, "tick" marks appear on the various fluid-quantity levels displayed, such as oil quantity, so the crew can readily monitor usage, or fluid loss.
On taxi out, a very noticeable cockpit bounce occurred at a medium taxi speed. I had to change the taxi speed to get out of this unpleasant oscillation.
The nosewheel steering handle has a gap to allow a map light to illuminate a table without a section of the wheel casting a shadow. This cutout, however, eliminates a portion of the wheel that captains typically grab for a hard turn.
Unfortunately, Boeing did not choose to improve a number of old design features, such as the magnetic compass location and the molding around the cockpit windows, which still leaks.
I taxied onto the runway, and we were cleared for takeoff. I stood the throttles up and then engaged the autothrottle system. The relatively high thrust-to-weight ratio resulted in a rapid acceleration. The takeoff EPR was 1.53 with a fuel flow of 7,500 pounds/ hour/engine (ppe).
The flight director limits the pitch attitude to 20 degrees nose up, and we were at that limit because of our light weight. Given the small windows and resultant poor visibility, this pitch attitude was rather uncomfortable. For as long as I have been involved with ALPA's evaluation of aircraft (15 years), I can remember complaints about the small size of the DC-9's windows. The windscreen size is probably one of the biggest legacies of the 1960s design. Most new airplanes have ample flight deck visibility, so the view from the cockpit of the B-717 was a bit disconcerting. No FAR, only an industry-recommended practice, addresses pilots' field of view from the cockpit.
The B-717 climbed well, passing 10,000 feet MSL 4 minutes after brake release. Our VNAV climb speed out of 10,000 feet was 289 KIAS. The B-717 had a very crisp and respectable roll rate. The rudder was very effective, positive, and definitely necessary for turn coordination. The pitch forces seemed just a little light to me.
We would be climbing to only 16,000 feet MSL on this evaluation.
Because of the limited time allotted for our flight evaluation, only 1½ hours, we would not have time to look at any of the high-altitude capabilities of the aircraft. The B-717 unfortunately is rather limited in high-altitude performance because of its relatively small wing.
At 16,000 feet, I evaluated the autoretract function of the speed brakes. When I advanced thrust above 75 percent, the speed brakes automatically and quickly retracted without any unusual pitch excursions.
I next performed a few steep turns at 45 degrees of bank and 200 KIAS--a relatively low speed--to evaluate the low-speed protection feature of the autothrottles. During steep turns, the throttles would automatically advance. Capt. Luczak could hold the throttles back to override this protection, but to totally disable it, he would have to pull the autothrottle circuit breakers.
I began to slow for the clean stalls. As I slowed, the amber band on the speed tape became visible at 199 KIAS. As I continued to slow, the "red zipper" or stall speed indication came into view at 163 KIAS.
The pitch limit indicator (PLI), which is continually in view, descended to indicate a maximum pitch of 10 degrees nose-up. The PLI probably could be made a bit more prominent; because of its small size, it was easy to overlook.
As I slowed to 163 KIAS, the stickshaker activated. A stick pusher is programmed to activate when a predetermined angle of attack (AOA) or AOA rate is achieved.
Stickpusher-inhibit buttons are provided on a gusset panel, one each, just to the left and right of the autopilot mode control panel. I was able to readily pitch the nose down to recover from the stall.
As a direct result of an argument made by ALPa's Airworthiness, Performance, Evaluation, and Certification Committee, the B-717 now has a maximum reverse thrust capability.
I know that the approved procedure for stall recovery is to apply maximum thrust, hold attitude to minimize altitude loss, and wait for the speed to build. But for the practical case of multiple approaches to stalls in an actual airplane, simply reducing the angle of attack (lowering the nose) will effect an immediate recovery, and will save considerable wear and tear on the engines. Actually, if altitude loss is not a factor, immediately reducing the angle of attack will effect an immediate stall recovery without the prolonging effect of attempting to hold altitude when there is no need to do so.
I got out of the seat to give F/O Hayes a chance to fly. He first lowered the nose to look at the high-speed handling qualities. Normal cruise is .76 mach with a Vmo of 340 KIAS and a Mmo of .82 mach. As the aircraft accelerated past Vmo, the throttles came back to idle, and an overspeed clacker sounded along with a voice stating "overspeed."
We then evaluated the airplane's ability to descend quickly. The best terminal descent performance is achieved with full speed brakes and 20 degrees of flaps. Unfortunately, this configuration yields a descent rate of only 2,000 fpm.
F/O Hayes set the flaps at 13 degrees for the next stall series. The amber indication appeared at 139 KIAS, and the stickshaker activated at 119 KIAS. In evaluating the B-717's handling qualities, F/O Hayes commented that the B-717 felt a little lighter on the controls than the MD-80.
Capt. Lutz took the seat for an approach configuration stall. With the flaps at 40 degrees and the gear down, the amber indication appeared at 130 KIAS, and the stickshaker activated at 110 KIAS. The Vref for this weight and configuration would have been 135 KIAS.
We flew our first landing with 40 degrees of flaps and intentionally included a lateral offset, to evaluate the airplane's handling qualities and maneuverability in the approach configuration. The fuel flow on final with flaps at 40 degrees was typically 2,300 ppe.
We all performed a number of normal patterns, V1 cuts, and single-engine landings. The aircraft was very docile and controllable during the V1 cuts. The single-engine climb rate was typically 1,100 fpm.
On one touch-and-go, after a single-engine approach, the pilot advanced the power before the rudder trim had been fully centered. An audible "rudder trim" warning sounded--a very nice feature--one that could have prevented at least one past accident.
On the final landing, we activated single-engine reverse thrust to look at directional control with one engine in full reverse. While the throttles have a nice feel, the detent for normal reverse was rather weak. This led to an inadvertent and unintentional activation of maximum engine reverse during rollout.
We appreciated the fact that the B-717 retained the maximum reverse thrust capability of the MD-90 design. Originally, airspeed limited reverse thrust on the MD-90; that is, at low airspeeds, only idle reverse was available. On a previous ALPA visit, we argued that for possible operational needs (such as for nil braking while approaching the gate), the airplane should have a maximum reverse thrust capability. As a result of ALPA's input, the design of the thrust reverse system was changed.
We exited the runway, and F/O Hayes taxied the aircraft back to the ramp. During our 1½ hour flight, the airplane consumed 8,300 pounds of fuel.
The B-717 does represent quite an improvement over the MD-80/88/90 series of aircraft, but it will not generally benefit from any of the advantages of being a part of a "family of aircraft," as is the case for the Airbus A318. However, the B-717 does have state-of-the-art engines and systems and uses the proven aerodynamic and structural design of the McDonnell Douglas twinjets.
Boeing says that this combination of new and proven designs provides the lowest cash operating cost of any airplane in the 100-seat market. The B-717 will be the only new 100-seat aircraft in service for the next 3 to 4 years.