Bjorn’s Corner: C Series flight controls

By Bjorn Fehrm

By Bjorn Fehrm

29April 2016, ©. Leeham Co: With the order by Delta Air Lines, the Bombardier C Series has taken the step up to be a viable alternative to Airbus’ and Boeing’s single aisle 130-150 seat aircraft.

In my description of airliners’ flight control and Flight Management Systems (FMS), I have focused on the established mainline single aisle players. Time to change that; C Series has arrived and will stay in the mainline segment.

Why 130 seats as a limit? Because below 130 seats there are a number of additional players (Embraer, Sukhoi, Mitsubishi…) and we can’t describe them all right now.

Now to how Bombardier has implemented the flight controls, autopilot and FMS for the C Series. In fact, we will look at how they have made the C Series cockpit, Figure 1.

C Series flight deck

Figure 1. C Series flight deck. Source: Bombardier.

I haven’t flown the C Series yet (working on it!) but I have been able to glean quite a bit over time and spent quite some time in the cockpit with the Bombardier test pilots at the Paris Air Show.

So here is a shot at describing the C Series control philosophies and capabilities and how they mimic/differ from Airbus and Boeing.

Flight control
C Series is a Fly By Wire (FBW) aircraft with a passive side stick controller, very much like an Airbus. As discovered during my A350 flight, this is OK. Active feedback sidesticks would have been better, but they were not available to the C Series project.

The throttles are like Boeing throttles; they are back-driven, i.e., one can see and feel when the auto throttle is working, which is good. This is typical of the C Series. It takes the best ideas from Airbus and Boeing and puts them together. In some instances, the C Series team had own ideas where they beat both the mainline legacies. One is the radio control panel. It is up at the glare shield (shared control panel with the display and navigation controls), where it should be, taken from their Biz jets.

The FBW flight laws are Boeing’s, as I understand it, i.e., the aircraft is speed-stable like a classical aircraft. I haven’t flown the Boeing laws, but had no problem with the C* laws for the Airbus. Look at my previous corners to get the lowdown on flight laws, here, here and here.

The FBW envelope protection is mostly Airbus. Angle-of-attack and load-factor have hard limits (Boeing also has hard limits for angle of attack for 787 when slats/flaps are deployed, I’ve been told), and this works well. High speed protection is a bit nicer done than Airbus. It reduces the throttles, but then it doesn’t raise the nose like the Airbus; it deploys the airbrakes. There is no change in the aircraft’s trajectory, a nice touch.

Avionics and FMS
The avionics suite is the same as for the Bombardier high end business jets, Rockwell Collins Pro Line Fusion, Figure 2. It has some really good features.

CSeries_ Flight Deck

Figure 2. Displays of C Series showing the avionics system from Rockwell Collins. Source: Rockwell Collins. Click to see better.

All display and control functions are made to keep the pilot’s eyes looking up and/or out.  The only important items on the central console are the throttles and the roller-ball/keyboard FMS input devices. Pro Line Fusion has total flexibility how the five large screens are used.

They can combine Primary Flight Display (PFD) with approach plates or Navigation Display (ND). Virtually any partitioning of the screens is possible. Note that the ND has both lateral and vertical displays, like the A350 and A380. A real important safety feature is the availability of synthetic 3D terrain superimposed on the artificial horizon for the Primary Flight Display. Instrument flying, which is hard work for the human brain, becomes a breeze with synthetic vision. Head Up Displays (HUDs) are optional for the cockpit and they show exactly the PFD picture, including synthetic vision.

The FMS is mouse-oriented with a tabbed interface, just like the A350 FMS. It seems to have a stricter flight phase structure than the more classical FMS on the Airbus jets.

The autopilot control panel (in the middle of the glare shield, in Figure 3 to the right) looks very much like that on the Boeing aircraft, which is good. I expect it to have the same logical division into Lateral and Vertical navigation modes. Airbus has a more mixed setup which has to do with their special throttle handling.

Figure 3. Glare shield placed display/radio controls (left) and autopilot controls (right). Above HUD, below PFD, ND and engines display. Source: Rockwell Collins. Click to see better.

What I like about the C Series that neither Airbus nor Boeing have is the glare shield-based radio controls. For the duopoly aircraft, this is a heads-down exercise, much better to have your eyes close to where the action is, your outside and the PFD/HUD. Overall, the heads up and out cockpit philosophy is commendable.

C Series is an aircraft project that has got a lot of tricky technical decisions right. It’s hard to find where they should have taken another path.

This hitting the right path at the junctures seems to have continued on the cockpit/pilot interaction side as well. Can’t wait to fly the thing.

28 Comments on “Bjorn’s Corner: C Series flight controls

  1. Good read as usual Bjorn!
    Two questions… on the pedestals between the rudder pedals are those trim controls (I couldn’t quite make it out in the photo)?. It would make sense as the pedestals seem almost like vestigial bases for a standard flight yoke. Were the C-series designed in the beginning to have standard yokes and later in the process went to side sticks?

    • Hi Geo,

      the pedestal you see in the middle between the rudder pedals it the cover over the rudder pedal mechanism. And on the front of the cover you have the wheel to adjust the position of the pedals, it’s not a trim wheel. C Series was designed with a sidestick from day one. With FBW you have no need for the force a yoke can give you (you need it for conventional part- or no- boost controls for this size aircraft), then you might as well go for a sidestick (today with force feedback), it gives you a better ergonomie in the work area.

  2. “the aircraft is speed-unstable like a classical aircraft” — should this be “speed-stable”?

    • Hi Matth,

      no it should not. A classical aircraft will have a slow movement of the nose in a nose down-gain speed-nose up-lose speed cycle, the Phugoid. This is normal and the nose down moment when the speed decreases is the charm with this behavior. It saves you from stall if you don”t pay attention to what the aircraft is doing. A FBW like Airbus and most FBW fighters prioritize that the aircraft keeps the attitude that it has, it’s like it is on attitude hold autopilot all the time. It gives a stable ride (for fighters a platform that stay stable when you work with the weapon system) but if your attitude is such that you lose speed it will fly you into a stall if nothing else is done to stop it (like Airbus and fighters hard stall protection). Read my previous posts to get the whole story.

      • Fair enough — I had understood from other news reports that the C Series control law would behave more like a classical aircraft (similar to Boeing’s FBW control law) in that it would require pilots to manually change the trim speed. Was that a misunderstanding?

        [Trying to track this down, I found the following from a March 2014 Aviation Week article: “While a basic C* FBW blends g force and pitch rate to control the pitch axis, Bombardier modified the control system to be speed-stable, meaning that it attempts to maintain a speed set by the pilot using the trim switches at the top of the sidestick.”]

        • We agree and talk about the same thing, the aircraft will go into a phugoid if let alone in the pitch axis. This means it will oscillate around a trimmed speed. I labeled that speed unstable because the speed will oscillate a bit around a trimmed speed but the correct way to call it is a “speed stable” system. The Airbus and fighter C* law is like an autopilot in Control Wheel Steering (CWS), point the A/C nose high and the speed will decay until the alfa protection increases thrust and commands pitch down.

  3. Thanks, Bjorn. Just a few quick questions. I’m surprised there aren’t two, center glare-shield, mounted, 4″x2″ FIRE warning light/extinguisher controls. (I guess engine fires just aren’t what they used to be–still kinda important, but no longer given the most prominent panel position real estate? Do the single red buttons on each side of this panel each control both engine no. 1 and 2 extinguishers?) What is the orange box–with the quaint toggle switch–at the back of the floor mounted panel? How about the device with the “Remove before flight” labeled tag in front of it? No ground tiller on board? And lastly, that “old school” mag compass, is it pilot adjustable for magnetic variation? (Is it actually even ever used anymore on airliners?) Thanks again. MO

    • The warning system in modern aircraft has a big caution lamp and warning lamp in the glareshield, you see it in Figs to the left and right. Then the rest of the information what it is that gives the Caution/Warning is presented on the central multi-function screens. If it’s something serious like an engine fire warning it could also be presented at the bottom of the the PFD or similar.

      All orange things in a test aircraft like this one (and the two at the extreme of the glare shield) does not belong to normal aircraft equipment list. It is the sign on test aircraft equipment. The device which the tag is attached to is the slats/flaps lever. The caution sign could be anything, just placed there so that the next crew will read it for sure before flight.

      There is a tiller to control the nose wheel steering on all airliners, outside of the sidesticks on the C Series and Airbus jets.

      Re compass, they are not normally pilot adjustable for magnetic variation, this is done once for all by engineers (with little magnets) and then there is normally a correction table for any residue corrections needed.

      • Thanks so much, Bjorn. Your responses were very on pointe and informative to me. But, just to clarify on “tillers”, there’s no tiller on board either CSeries or Airbus aircraft? (I can’t see any in these cockpit photos.)

        • You can just glance it to the right of the right sidestick and behind the pilots seat. Check other C Series cockpit photos and you will see it, it is there on both sides.

  4. A peanut-gallery question I suppose, but why the notched seats for the crew. With a side-stick and nothing between the legs I’d think the notch in the seat wouldn’t be necessary?

    • I think it is for the 5th belt strap to give it a correct path, the one that goes from the seat up between your legs. Pilots strap in quite well, normally with 5 straps.

  5. Great to see Cseries getting the recognition for the innovation and technology it is bringing to the table. It would be great to hear from an experienced pilot like you what this means in terms of workload and safety when compared to the MD-88 it will be replacing at Delta.

    • Thanks Mark,

      I’m not an experienced pilot for an airliner but have been in the cockpit many times when my Air Force colleges that went to e.g. SAS have flown the MD series. There is not question the C Series will be easier to fly. The set-up and choices are top notch and I thrust the C Series team to have done a good implementation.

      What I especially see as a major safety improvement is the availability of Synthetic Vision. Having read the reports from the recent stall related airliner crashes it’s clear these pilots have been gravely disoriented.

      Synthetic Vision really helps with that. It is the only thing in my mind that can fix the problem of pilots spending 5-10 years flying FMS based autopilot flights and then suddenly be asked to fly on base instruments in a highly stressed and disoriented situation. Only fighter pilots get the real life training to sort this out. This is trained day in, day out in real flight situations and we learn to almost disregard instruments like speed and altitude when things go pear shaped. Just get your nose pointed correctly through the artificial horizon and things will sort themselves out. Then you verify on secondary instruments.

      Synthetic Vision, if correctly implemented, means the airline pilot can fly on the primal visual cues out of sudden extreme situation. He will fly on the real horizon then (his brain sees it as the real horizon), like he learned in primary flight training, and not on the data from the secondary instruments. Flying on secondary instruments data can be lethal. Not because they are incorrect, but because you NEVER EVER EVER pull the stick on that data. You first check your attitude and then decide what change is needed in your attitude to correct the situation.

      This is instrument flying basics but the modern cockpit scan pattern, while on autopilot, destroys this basic learning. Nothing happens on the artificial horizon for 10 years worth attention so why look at it twice as often as the secondary instruments (which is correct instrument flying).

      • I can think of so many tragic accidents that would have been avoided by the synthetic vision. I hope Delta did not cheap out on this feature as they are notorious for penny pinching.

        • It’s a software addition to Proline Fusion so even if Delta doesn’t order it from day one it can always add it as a software update later.

    • Deltas MD88s are configured with 2 class 149 seats, so I dont see a CS100 replacing that.

      • I was on a CS 300 yesterday that had 150 seats set up in one class but you are right. Even if they switch from CS100s to CS300s, it will not directly replace the capacity of the MD88s. There is some speculation that Delta asked for a CS500 which may be announced at Farnborough this summer.

        • It may not be a direct replacement, but it sure can be used to vary capacity by season and by time of flight, in conjunction with other fleet types.

  6. Excellent article, although one thing you didn’t mention that bombardier will implement Enhanced Vision System (EVS) into the C Series, something I understand is already available in their Global Series business jets. This should make low visibility approaches easier. I am not sure if this is available on any other commercial aircraft such as Boeing or Airbus models, although I do remember reading somewhere that it may be added to the A350. As an experienced pilot what is your opinion on the value of this technology, and have you personally flown it?

    “Sometime after initial operations other options will be available, including Rockwell Collins’s synthetic vision for head-down and head-up displays, as well as enhanced vision systems.” (

    • Hi Dan,

      I have never flown an IR camera enhanced vision system (EVS), such thing are pretty new. It will probably be helpful, especially in a Biz jet environment where you land on small airports. On mainline airline airports you normally have ILS or RNP class GPS RNAV landing procedures. ILS ones have minima of 200 ft over threshold all the way down to 0 for CAT 3 systems. I don’t think an EVS gives you lower minima and therefore you would have to abort an approach if you don’t have the visual contact at 200ft even if your EVS shows you are on the right path to hit the threshold. Until it changes your minima (which requires a lot of certification work by Rockwell Collins) its additional worth in an airline situation might be questionable. For Biz jets it could be useful, you land on smaller airfields, it should bring improved situationnel awareness which is never bad.

  7. Bjorn:

    I see the backup attitude indicator on the central panel, but I do not see the VSI, turn and bank or the altimeter?

    Maybe I am old school but those (now backup in the attitude indicator) and the rest were the alternatives under instruments if you lost a primary.

    I also do not quite get if the side stick is cross connected so that either pilot knows what the other is trying to do?

    The moving throttles seem like an excellent idea.

    Not so sure about the synthetic vision, it seems more a tool to get in under minimums, i.e. operational. Along with HUD a good tool, but any safety seems to be more in the real of general aviation where as you noted they poke into small airports in bad conditions.

    It seems that most of the recent accidents none of the aids helped really bad piloting (along with bad oversight in the case of both AF447 and Asiana 214 crash with experienced pilot in the cockpit or got up to the cockpit in plenty of time)

    And I know I repeat myself but it seems that the moving throttle should be standardized not optional so that as in the past with the move to the T instrument setup, it was common across the industry and someone transitioning from an Airbus to a Boeing would not “miss” what was going on.

    • Hi Transworld,
      the standby display you see in the middle has it all. It is a new generation Integrated Standby Flight Display (ISFD) which is a copy of the PFD with own integrated inertial and air data unit. It means it measures and calculates speed, altitude, heading, sideslip and displays VOR and ILS data. This might be the Meggit iSFD but others make them as well (the Airbus ones are from Thales called ISIS).

      The sidsticks are not cross connected, the project looked carefully into if they should be and decided that it would not be ideal. With the BAE forcefeedback sidestick being available that was developed for the F35 and which KC390 and MC-21 use the decision might have been another.

      Re synthetic vision, do you mean enhanced vision ie IR camera augmented or synthetic display of the ground on the PDF and HUD?

      • Bjorn:

        That is a new one on me, ISFD, have not kept up with it obviously.

        All in one and all in one possible failure or just in the same frame and all independent?

        Not sure on the vision part, I am familiar with HUD and the aircraft flying display, synthetic on it as well now?

        I though camera was the only way but again missed that if not true.

        • It is one unit which could fail, but then you have several levels of degradation of your normal instruments before you would land the aircraft on the ISFD. Finally one has to land like in the old days I guess, find a hole in the clouds and charge down!

          There are two kinds of vision help;

          The Synthetic Vision which is a graphical representation of a 3D ground contour database (the one I say is a must going forward) and

          Enhanced Vision which is an IR camera making video of your forward vision. My argument is that your Mk 1 eyeballs are good enough for the airfields that commercial aircraft fly too given the landing aids on such airfields. Not so for Biz jets.

  8. Can I ask if the a220 is similar to other ab types and has a pilot work table ?

Leave a Reply

Your email address will not be published. Required fields are marked *