E175/190 question.

[Nark]

According to our Quick Ref Handbook if we lose hyd system 1, of the associated items lost , you also lose the autopilot. However you don't lose the autopilot with a system 2 hyd loss.

Why is that?

[Stu Pidasso]

W.A.G.

Autopilot runs off Hydraulic System One.

How's that for a guess.....?

[Nark]

Swing and miss!

The Autopilot doesn't really have anything to do with the hydraulics. Only do far as, it limits control deflection as a function of airspeed, yaw damp and thrust modes.

But the question still stands since both systems run various control surfaces, why does a lose of system 1 degrade the A/P but not system 2?

Also, the controls are 'powered' through servos in the cockpit, completely separate from the Hyd system logic.

Just curious if any AC bubba have run across this?

[BlueSkies12]

You should ask a contract instructor.
Although they won't know the answer they'll act like they do and make up something entertaining i'm sure.

[Xander]

My best bet would be that the AP servos are connected to the LH outboard elevator, upper rudder and and MF spoilers L and R panels 3 and 4.

[unregistered]

You should ask a contract instructor.
Although they won't know the answer they'll act like they do and make up something entertaining i'm sure.

[wordstwice]

When you lose #1 hydraulics you lose half the elevators and half the roll spoilers. This would then require too much torque for the autopilot servos to overcome hence you lose the autopilot.

Now, to answer why you keep the AP if you lose the #2 I would be taking a somewhat educated guess so I wont bother....

[Nark]

Spoke with a mechanic:
System 1 controls yaw damp, which is needed for AP.

Hence the lose of AP.

[wordstwice]

Thats interesting because the Yaw Damp runs off both the #1 and #3 hyd system. Been years since I've been current on the Embraer so take that for whats its worth

[JZA]

Isn't this a question you could ask your Chief Pilot/Fleet Manager or Instructor? ... Probably a better source (in theory) than a public forum IMO. Good luck.

[Cap'n P8]

Interesting. I believe that although the YD will automatically turn on when AP is selected on (if the YD was off at the time,) you can select the YD off and the AP will continue to work. If that's the case then it probably wouldn't be the reason you lose the AP with loss of system 1.

[Nark]

JZA
This is precisely why I came here. I was "polled" by a check airmen during my last flight. It's one of those questions that's floating around.

The issue is that no one can get a definitive answer. Most other system quarks has a foundation somewhere in Embraers logic, but this one is the flavor of the day I guess.

Thanks so far for the input.

[Cap'n P8]

Just asked a fellow in our training department. He suspects it was a certification issue with Embraer. He is going to ask Embraer, I'll get back when I hear what he has managed to dig up.

[MRP]

My guess is that its something to do with the multi function spoilers and Normal vs. Direct mode. Hyd 1 and 3 operate various spoilers on each wing. Any abnormalities in controlling the spoilers will cause the FCM to revert to direct mode, which in turn will cause the AFCS to disengage.

[Cap'n P8]

Just got the word back. With the loss of Hydraulic system 1, and the associated loss of multifunction spoiler pairs 3 and 4 the autopilot will automatically disconnect in a turn. For this reason they decided to have you manually disconnect the autopilot and hand-fly.

[Nark]

Thanks. I was initially on the right track with that, however I couldn't connect the dots.

I appreciate it.