The 787's digital fly-by-wire flight-control system architecture is similar to the 777 and it uses the same C*U (pronounced “Sea Star U”) pitch control law. C* means that fore/aft yoke movement commands pitch rate on the ground, and g rate or vertical acceleration (Nz) in the air. U means that speed stability is built into the control laws, so the pilot has to manually trim pitch in flight with speed changes.
A number of new FBW enhancements are on the 787. Roll control now is fully fly-by-wire. There is a “P-beta” yaw and roll asymmetry compensation function that uses inertial inputs from the Earth reference systems to counter weathervaning during crosswind takeoffs and landings plus thrust asymmetry during an engine failure.
Maneuver load alleviation progressively extends the outboard spoilers during high-g conditions to reduce wing-bending stress. Gust load alleviation also extends the spoilers and deflects the ailerons to reduce wing-bending in turbulence with the autopilot engaged. Autodrag helps the flight crew descend from above to capture glideslope/glidepath while maintaining airspeed at idle thrust by deflecting the ailerons downward and outboard two spoilers upward if the landing gear are extended and flaps are set to 25 or 30 deg.
Tail-strike protection decreases the risk of ground contact during takeoff and landing by decreasing elevator deflection. The cruise-flaps function automatically adjusts the flap, aileron, flaperon and spoiler positions at Mach 0.54-0.87 above flight level (FL) 250 to optimize wing camber for cruise efficiency.
When boarding the aircraft, I noted that the L1 main entry door is located relatively close to the left angle-of-attack (AOA) vane. Airlines are advised to train ground crews carefully in how to position the passenger boarding bridge to avoid damaging the AOA vane.
I strapped into the left seat of ZA005, the fifth flight-test article, with Capt. Mike Bryan, assistant chief 787 pilot, in the right seat as instructor and Heather Ross, 787 engineering project pilot, riding along in a jumpseat as safety pilot.
We used 115Vac ground power to supply the avionics and systems prior to APU start. Notably, ground electrical power can be used to supply the cabin pressurization pumps and thus air-condition packs. With at least two ground power sources, preferably three, the main engines also can be started on ground electrical power. However, airline operators say that the aircraft is sensitive about the quality of ground power, so voltage, frequency or amperage variability may affect aircraft electrical system performance.
Bryan explained that Boeing FBW aircraft have back-driven and interconnected yokes and rudder pedals, along with back-driven throttles and speed brake handles, that provide visual and tactile cues of what is going on in the cockpit. This is in contrast to some FBW aircraft fitted with side-stick controls that are not interconnected or back-driven and auto-throttle systems that do not move the thrust levers. It is more difficult in such cockpits to keep all flight crewmembers in the situational awareness loop, Boeing engineers assert.
But, Bryan also says that, unlike the 777, the 787 has no dedicated control display units for the flight-management computers (FMC). Multifunction keyboards on the center console are used to enter characters in the scratchpad field of a virtual control-and-display-unit (CDU) graphic on any one of three display screens. The scratchpad contents then are transferred into selected fields using a touch pad cursor control device. Without dedicated FMC CDUs, I would prefer a touchscreen user interface in place of the cursor control device entry method.