Boeing's opinion on the Airbus side stick...

[LH-B744]

Holy thread revival!

Yes. I'm not even sure if I hadn't already contributed here since UALdave opened the topic, in 2009!

But probably this is the reason why jetphotos is a great platform. Topics are opened, and almost a decade later, the author of that topic has not vanished. I've just read how UAL opened this topic (his #1).

'Why was Captain Sullenberger able to operate his A320 like a Hudson ferry boat, and all 155 souls on board survived?'

To answer that question with a comparison between A and B, a deeper understanding of an A320 is needed. Which I don't have, but..

Gabriel, that's what I also had in mind after I left the theatre in December '016, when the Sully film was shown. If Captain Sullenberger were a veteran B737 flight captain, the result must've been the same.

Or is there a difference between 320 and 737 concerning the behaviour as a ferry boat (land on water and float)?
I don't own a semipro 737 simulator so that I could try something like that.

[Evan]

True, although I don't know if the side stick in an Airbus gives the same amount of feedback as one used for flight simulator-ie, the Airbus one might feel tighter, in terms of movement.

The main thing to understand here is that neither Airbus nor Boeing FBW jets are directly flown by pilots in normal operations (aside from takeoff and flare); neither is directly trimmed either. Each is using pilot commands as 'intentions' and interpreting them through C* and C*U control laws. Both the sidestick and the yoke are mere interfaces for a flight control system.

If you compare the Airbus and Boeing FBW methodologies, the most apparent difference is in trim. Airbus FBW jets use a workload reducing autotrim function and thus have no purpose for artificial-feel backdrive whilst Boeing FBW use traditional yoke pitch trim switches (functioning as a trim speed selector, driving an autotrim function) and must employ a trim force backdrive for feedback.

It starts in the 1960's when the C* algorithm was first developed. NASA was developing the sidestick control methodology for the Apollo program and subsequently used center-stick traducer controls in the space shuttle. Airbus naturally adopted it for next-generation flight control and the A320 was bleeding-edge technology in the mid-1980's. C* FBW enabled them to eliminate a significant element of pilot workload: the need to retrim for variations in speed and configuration. That's a forward-looking, evolutionary philosophy.

Boeing, on the other hand, wanted a methodology that wasn't a game-changer, but rather a natural evolution for pilots transitioning from non-FBW jets. That's an understandable and cautious philosophy.

The problem presented by FBW flight control systems (very complex and greatly simplified here) is longitudinal static stability in manual flight. Neither the Airbus nor the Boeing FBW enables the pilot to command stabilizer trim directly in normal operating law (aside from rotation and flare). Thus, to get certification, Airbus needed to add envelope protections, while Boeing uses a C*U control law, where the primary trim switches actually adjust the trim speed directly (and the FCC's command stabilizer trim accordingly) and an artificial backdrive provides column force feedback.

That's basically the difference in pitch control interface. Boeing C*U must provide a means for trim feedback. Airbus does away with manual trim altogether (aside from take-off/rotation and flare) and thus needs no feedback loop to the pilot.

Now, what are the issues in real world experience...

Mainly, awareness. On two factors.

The first factor, which can be absolutely critical, is positional awareness of the stabilizer. As I said, in BOTH Airbus and Boeing FBW, the trim is set by the flight control computers, so awareness is needed. Boeing does this traditionally by using backdrive force on the column. Airbus uses graphical displays as well as a moving trim wheel on A320/330/340 models. Experience has shown us that in high-stress situations, that is not always enough as pilots cannot focus on visual feedback alone. The A320 that crashed outside of Perpignan, France in 2008 (due to frozen AoA sensors, the result of negligence by maintenance crews) had stabilizer trim deactivated (as per design in alpha prot) in the full nose-up position, and along with TOGA thrust pitch coupling, the elevator did not have adequate authority to overcome the resulting pitch-up effects. All the crew needed to do was lower the stab trim, but they had no direct feedback to identify that trim was the problem.

A modification of software to always inhibit pitch trim in the ANU direction within the alpha protect regime would probably be a good idea... Training pilots to always use pitch trim when elevator is insufficient, along with moderate thrust rather than abrupt TOGA, is essential.

The second factor is pilot awareness of each other's actions. With a yoke, each pilot can clearly see what the other is doing. With a sidestick it is more difficult. Now, that said, under no CRM circumstances should both pilots be simultaneously flying a FBW jet, so the real issue there is CRM, not interface, but we also know that CRM tends to go out the window under certain conditions of stress, fatigue and weak training. Airbus also provides a clear "DUAL INPUT" annunciation and a visual indication. Still, that's not as obvious as a yoke and it doesn't tell you what actual commands are being made by the other pilot.

So, for me, the bottom line is this: Reducing pilot workload (pitch trim) removes a distraction/stressor that has caused crashes (and many hard landings) in the past and seems like a sound evolutionary move. However, removing force-felt trim feedback and visual cues between pilots presents new risks when things go awry.

So which is safer? It's a trade-off really, or as MCM put it, horses for courses.

In any case, both are safe enough in the hands of well-trained, well-rested pilots, so maybe we should start there (Airbus did).

[3WE]

...Reducing pilot workload (pitch trim) removes a distraction/stressor that has caused crashes (and many hard landings) in the past and seems like a sound evolutionary move. However, removing force-felt trim feedback and visual cues between pilots presents new risks when things go awry...

Indeed...but...

...But I've been pulling up the whole time...

I don't think we really know what he was thinking.

I do find the situation that: This airplane does not behave like an airplane until things get really unusually bad...

...and then it behaves like an airplane...

kind of lacks 'failsafe logic'.

Something that always behaves like an airplane C150, 737-236A, ERJ-45, 787...but not_Airbus...seems like a better situation- especially when things get real bad and you don't know whether you are dealing with solidly-protective HAL or a really big 172 that will somewhat gently but expeditiously mush down to the ground from high cruse altitudes.

Of course, it's also amazing what aircraft will do for short time periods at known power and attitude settings...while consulting the exact right QRH checklist (which offers up known power and attitudes in scientific printed tables).

[3WE]

...is there a difference between 320 and 737 concerning the behaviour as a ferry boat...

No real hard data to back this up, but it sometimes seems like those cheap composite hulls hold up pretty good compared to the Boeing counterpart...How often to you get a largely-in-tact aircraft after a ditching?