Glad I'm not a passenger

Thread Starter

cmartinez

Joined Jan 17, 2007
8,783
Dang it! ... I hate it when the flux capacitor does that!:


News Fail: Cranland Skydiving Accident blamed on Flux Capacitor

 

Thread Starter

cmartinez

Joined Jan 17, 2007
8,783
A slight miscalculation:


The crew miscalculated by almost 90 tons, Business Maverick was informed. With an error like this, the take-off speeds are calculated as far too low (low TOW, low takeoff speeds). Fortunately, the Airbus is designed to correct these speeds, but not the speeds for flap retraction. Thus when the crew retracted the flaps the plane went into “alpha floor” event. This is where the airspeed is too low and the aircraft is in danger of stalling. A disaster was averted because once again the aircraft’s safety systems took over, adding power and lowering the nose slightly, preventing it from stalling.
 

bogosort

Joined Sep 24, 2011
696
A slight miscalculation:
Years ago, I was fortunate to get several hours training in Airbus level-D simulators (https://en.wikipedia.org/wiki/Full_flight_simulator) for the A320. On my last session, I asked the instructor if I could try to put the airplane in a spin. He reluctantly agreed -- I think he was curious if it could be done -- and so he put the flight controls in direct law (all protections, including alpha floor, disengaged). We quickly found out two things: 1) an A320 will indeed spin, and 2) the physics of a spin make the simulator a very uncomfortable place to be.

The simulator started yawing and thrashing us around so wildly and violently that I immediately tried to recover. Unfortunately, my experience with spins is limited to Cessna 172s, and what easily works in a 172 does not in an A320. Meanwhile, the instructor (unbuckled in the back) was being tossed around the flight deck. He finally managed to hit the kill button, bringing the very expensive machine to a sudden stop. He was not happy with me.
 

MrChips

Joined Oct 2, 2009
34,870
Aren't those machines protected against damage in those extreme scenarios?
You have to always expect the unexpected. Thus in my CNC build, I have implemented two kill buttons.
One soft button sends an eSTOP signal to the SW controller that then shuts down all motors.
A hardware emergency kill button cuts AC power. This is a latching NC switch that has to be twisted to reset.
I am sure that in your line of work you see this all the time.

1616603180095.png
 

bogosort

Joined Sep 24, 2011
696
Aren't those machines protected against damage in those extreme scenarios?
I don't know how close we were (or if we exceeded) the mechanical limits of the simulator, but the movement was so violent and jerky that it did not feel safe. It seemed like the software, trying to simulate out-of-envelope physics, was giving the hydraulics wildly discontinuous control inputs. One would think that the software would have stricter limits than the mechanisms, but these things are as complex as the airplanes they simulate. There may be good reasons to allow "unlimited" software outputs in zero protection mode, and simply warn against such situations in the manual.
 
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