Sunday, June 07, 2009

Birds of two kinds

I have a nesting pair of Cooper's Hawks in my yard. Strange vocalizations (but much different than the Red Tailed Hawk sounds you hear on movie soundtracks a lot). Not surprisingly, I no longer have a pigeon problem.

A website about metallic birds is one of my new favorites. In the entry on the AF Airbus 332 crash there's an interesting timeline of the automatic messages sent from the avionics:

02:10Z: Autothrust off
Autopilot off
FBW alternate law
Rudder Travel Limiter Fault
TCAS fault due to antenna fault
Flight Envelope Computation warning
All pitot static ports lost
02:11Z: Failure of all three ADIRUs
Failure of gyros of ISIS (attitude information lost)
02:12Z: ADIRUs Air Data disagree
02:13Z: Flight Management, Guidance and Envelope Computer fault
PRIM 1 fault
SEC 1 fault
02:14Z: Cabin Pressure Controller fault (cabin vertical speed)

At 2:10Z time, "FBW alternative law" says that the fly by wire system switched algorithms from, essentially, one that prevents pilots from potentially hurting the plane to one that allows pilots to do drastic things that shouldn't happen during normal flight. TCAS is the Traffic alert and Collision Avoidance System, a favorite among computer scientists interested in software safety and critical systems, like Nancy Leveson. The pitot tubes, along with static ports, are basically how the the instruments figure out how fast the plane is flying through the air.

PRIM 1 and SEC 1 are the primary and secondary flight control computers.

Airbus and Boeing take different approaches to FBW, you might want to read about it. There's more about the Airbus 330 system at Reply 12 (I couldn't figure out how to link directly to the post) in this thread.