News from ALPA's Committees
ALPA Flies the EMB-170
|Aircraft Design and Operation Group|
By Capt. Terry L. Lutz (Northwest)
Air Line Pilot, August 2004, p.24
In mid-2003, Capt. John Cox (US Airways), ALPA’s Executive Air Safety Chairman, directed that ALPA safety representatives become very knowledgeable about all fly-by-wire airplanes produced for the airline industry. Our safety concerns focused on embedded software that can contain limitations and mode changes that can take pilots out of the control loop.
Embraer was about to introduce a new family of airplanes incorporating FBW technology. Our excellent working relationship with the company, built up over several years, allowed us to set in motion a visit to fly one of the test-configured EMB-170s.
The ALPA Air Safety Committee did a lot of preparation work well in advance of our visit with Embraer. First, we put together a team of three pilots with special talents in aviation safety, aircraft development, and Embraer-specific characteristics—Capt. Cox, First Officer Bill DeGroh (American Eagle), and I. To become as familiar as possible with the airplane before the test flight, we asked Embraer to send us a complete package of flight manuals, emergency procedures checklists, and the quick-reference handbook. The Brazilians graciously complied with our request.
In addition, before the test flight, Embraer was able to schedule some time for our team in the EMB-170 full-flight simulator that was nearing certification at CAE in Montreal. In the simulator at CAE, we were able to see things that we could not have seen in the airplane, such as using flightpath and flight director guidance for windshear recoveries; our sim time prepared us very well for flight in the real airplane.
The airplane we flew, PP-XJS, was one of 8 flight test airplanes from the manufacturing facility at Sao Jose dos Campos, Brazil, about an hour’s drive from Sao Paulo. Our test pilot for the evaluation was Capt. Jurgem Prust, and the flight test engineer was Jeronimo Goellner.
The EMB-170 is a big airplane. You can stand up in the cabin, and both seat size and overhead bin space are designed to meet the needs of the business traveler.
External inspection reveals an aerodynamically efficient airframe. We saw only two airflow modifiers—a tiny fence on the outboard end of the leading edge slats, and strakes on the engine nacelles.
Embraer has designed cockpit systems and switches to meet the "dark and vertical" concept. A quick look at the overhead panel confirms this, and reveals some new features, such as a rotary switch used to balance fuel by automatically opening/closing the crossfeed valve and turning on/off fuel pumps when the fuel is balanced. A push-to-talk switch mounted on the glareshield is easy to reach, and you can keep your eyes up and outside when you want to transmit. During our cockpit evaluation, the only potential problem area we noted was the location of the circuit-breaker panel, which is right next to where the captain’s flight bag is stowed.
Innovation on the flight deck includes tuning the radios and setting transponder codes in the multifunction control and display unit (MCDU). A single knob on the MCDU is used to manually tune any nav or comm frequency. Buttons on the audio control panel control transmit and receive functions, but a master volume control knob adjusts the volume of the most recently selected audio button.
The Honeywell Epic primary flight display (PFD) is excellent. The flight mode annunciator (FMA) display at the top of the PFD has two lines and for 5 seconds after a mode change will flash in a light/dark pattern. The autopilot controls are on the glareshield, and the pilot must look at the FMA to observe the changes that are entered on the glareshield controls.
Target airspeeds, altitudes, and vertical speeds are well marked on the PFD. The most important and innovative feature on the PFD is the flightpath marker, which is used for control instead of pitch attitude. We also found the system displays, in particular the flight control display, to be detailed and intuitive.
Wind can be shown on the PFD as a single vector with digital readout, or as headwind and crosswind components relative to flightpath. This is very useful when operating near the crosswind limit of the airplane, which is 30 knots. If runway conditions are less than dry, the aircraft operations manual contains an excellent depiction of crosswind limits based on runway surface conditions.
Starting the CF-34 engines is automatic, using start buttons mounted ahead of the thrust levers. For the EMB-170/175/190/195 family of airplanes, engine thrust will vary from 14,000 to 18,700 pounds per engine.
The size, height, movement, and feel of the thrust levers are ideal. With autothrust engaged, the thrust levers become moving autothrottles.
Visibility from the flight deck is very good, and you can see the wingtip from the pilot’s seat. We found taxi handling to be excellent whether we were using the tiller or the rudder pedals. The steer-by-wire and brake-by-wire systems are smoother and more positive than those of some larger airplanes with the same configuration.
Our takeoff from Sao Jose dos Campos was at a weight of 66,670 lbs, including 17,600 lbs of fuel. At that weight, our target speeds were V1=109 KIAS, Vr=112 KIAS, and V2=122 KIAS.
At 15,000 feet and 280 KIAS, we had our first in-depth look at Embraer’s FBW design. The EMB-170 elevators, rudder, and roll spoilers are FBW. The ailerons are controlled mechanically.
Instead of using complex control architecture, Embraer chose proportional control, which means that control surface movement is proportional to pilot input. Although pitch rate and alpha rate feedback are used, the EMB-170’s FBW system is primarily an alpha command system. The only active limiter is an angle-of-attack (AOA) limit.
Four digital computers called FCMs (flight control modules) are primary and provide inputs to analog P-ACE (primary flight control actuator control electronics) computers. They serve monitoring and standby functions in normal mode. In direct mode, the FCMs are removed from the control loop, and control limits default to values set in the P-ACE computers.
Pitot-static, AOA, and sideslip information are provided by four "smart probes" mounted on the nose. The smart probes provide electronic signals to the instruments and flight control computers. The EMB-170 has no pitot-static lines, and no AOA vanes.
We found the control forces in all three axes to be lighter than in other airplanes of comparable size. The EMB-170 FBW system does not provide auto trim, but we found trim change with airspeed change was small, even at the forward center of gravity of the test airplane. Roll rate was crisp, ranging from 15 deg/sec at half deflection of the roll controls to 30 deg/sec at full deflection. Full rudder deflection at 230 KIAS produced 6 degrees of sideslip, requiring 6 degrees of opposite bank to maintain heading. The EMB-170 exhibited well-behaved Dutch roll characteristics with the yaw damper off, making only 7 oscillations from a sideslip release.
These are all normal characteristics. We concluded that, because of the EMB-170’s straightforward, predictable handling characteristics, if you weren’t told this was a FBW control system, you wouldn’t know.
We explored stalls in both normal mode and direct mode. In normal mode, the FCMs limit AOA. The airplane will approach the stall until just past stickshaker, when the FCM limits AOA in light airframe buffet. In direct mode, we flew full-aft-stick stalls with no AOA limit. In moderate buffet, we could easily roll the airplane into a precise bank angle and hold it.
The minimum airspeed we saw during stalls was 78 KIAS with full aft stick. In a turning stall with 30 degrees of bank, we saw 94 KIAS; and in 55 degrees of bank, the onset of stickshaker occurred at 114 KIAS. We experienced no wing drop and no heavy buffet. Stall recovery involved simply reducing back pressure and adding thrust, with little or no altitude loss.
During our airwork, we had our first opportunity to fly the EMB-170 while using the flightpath marker as a reference. From our simulator work, we knew that we could control altitude precisely with the flightpath marker during a steep turn. When we tried it in flight, the turn was so precise that we flew through our own wake! Pilots flying this new airplane will immediately adapt to the flightpath marker.
The flight director guidance cue is a magenta diamond. It makes tasks like intercepting and tracking the ILS both simple and exceptionally accurate.
In the simulator, we were able to see how Embraer has used the flightpath marker and the full performance of the airplane to handle windshear recoveries. If the airplane enters windshear, the flight director commands a flightpath angle that represents optimum performance of the airplane. In addition, when the pilot advances the thrust levers to maximum thrust, any limits previously set to save engine life are removed, and the full rated thrust of the engine is available.
We think that this optimized windshear recovery system should become the airline industry standard. Embraer incorporated these very important features in the EMB-170 as a direct result of inputs ALPA made in 2001 during the design process.
We did some pattern work at the new facility Embraer has built in the midst of orange groves at Gaviao Peixoto (GPX). The runway there is nearly 15,000 feet long, and the middle 5,000 feet is perfectly flat for testing Vmcg and wet runway performance.
As we descended toward GPX, we evaluated the speedbrakes. Manual extension of the speedbrakes on the EMB-170 is smooth with no pitch change at extension or retraction. The speedbrakes produce moderate buffet at full deflection.
Both ALPA and IFALPA have developed policies that urge aircraft manufacturers to provide automatic speedbrake retraction as a standard feature, and Embraer embraced this concept in the new design. Based on speed, configuration, and throttle position, speedbrakes deploy automatically at touchdown and during rejected takeoffs, and retract automatically during go-arounds. If the speedbrakes are not in a position called for by the handle, an EICAS "SPDBRK LEVER DISAG" message will appear.
We tested the EMB-170’s ability to descend rapidly by engaging the autopilot, selecting a lower altitude, retarding the thrust levers to idle, and selecting a speed just below Vne. With speedbrakes extended, the stabilized rate of descent was slightly more than 10,000 fpm.
At GPX, our evaluation included normal landings, engine cuts at V1 and at V2+10 during go-arounds, and single-engine patterns and landings. Because the runway is long enough for stop-and-go landings, Capt. Cox was able to make a full-stop landing with maximum antiskid braking.
We all noticed the EMB-170’s light rudder forces. Each of us overcontrolled slightly with the rudder during our first takeoff. This is a training consideration for transitioning pilots, so they can adapt readily to the light forces and not overcontrol in crosswinds, during an engine failure, or on slippery runways.
V1 cuts in the EMB-170 require full rudder deflection, and deviation from centerline is about one-half the width of the landing gear. The rudder trim control is on the aft edge of the center console; it has a timer that limits a single command to 3 seconds. Then the pilot must release the knob and reapply rudder trim. Applying rudder trim in 1- to 2-second bursts seemed to work very well. With engine failure at V2+10 during initial climb, airspeed decayed predictably to V2 as rudder was applied to compensate. During the one landing rollout when Capt. Cox applied maximum antiskid braking, deceleration was very smooth. We perceived no cycling of the antiskid system or chirping tires, and directional control was excellent during the rollout.
Our final landing back at Sao Jose dos Campos was from a simulated Cat II approach, with the autopilot and autothrust engaged. We had flown 3 hours 43 minutes, divided among the three ALPA pilots, and burned 14,100 lbs of fuel for an average fuel burn of about 3,800 lbs/hr.
Using careful aerodynamic design and a robust FBW system with excellent handling characteristics, Embraer has placed itself solidly on the world stage as a major aircraft manufacturer. Pilots transitioning to the EMB-170 will need to adjust to its lighter control forces but will enjoy the nimble, predictable feel of the airplane.
Less training focus is needed on the EMB-170 FBW system than when transitioning to other FBW airplane types, and training emphasis can be placed on the complex relationship between the autoflight and autothrust systems, which are the keys to efficient line operations. Although the flightpath marker is a new concept, pilots will readily adapt to it and with experience will find more ways to use it effectively.
Mid-Atlantic was the EMB-170 launch customer in the United States, and ALPA pilots are flying these airplanes. Based on our first look at Embraer’s newest product, and the excellent communications we have with Embraer, the EMB-170s entry into service should have been very smooth.