Kenneth Tilton  <kentilton@gmail.com> wrote:
+---------------
| Rob Warnock wrote:
| > And guess what?!? The Dutch Safety Board says that the Turkish Airlines
| > plane *was* on an autoland approach when the altimeter failed!
...
| >      According to the Flight Data
| >      Recorder, the airplane was on a full autoland approach at a
| >      height of 1950 ft / 595 m when the left Radio Altimeter suddenly
| >      misreported a height of -8 ft. The autoland system responded
| >      accordingly...
| 
| yeah, what am I gonna do?, the altimeter says 1950 then it says -8, I 
| have to respond accordingly--I ignore the broken altimeter!!!!!!
+---------------

Of course, if you're landing on Catalina Island:

    http://en.wikipedia.org/wiki/Santa_Catalina_Island,_California
    ...
    Catalina's airport, the "Airport in the Sky" (AVX), was completed
    in 1946. The 3,250-foot (990 m) runway sits on a mountaintop,
    1,602 feet (488 m) above sea level.

then the radar altimeter going from 1,602' to -8" instantly would
be perfectly *normal*!! The approach end of the runway extends all
the way to the edge of the cliff, you see:

    http://airports.pilotage.com/avx/
    ...
    The approach end of Catalina's runway 22 begins at the edge of a
    1500' cliff. This gives the airport some characteristics similar
    to landing on an aircraft carrier that is 1,602' in the air.
    ...

[Yes, I know that AVX isn't approved for Cat IIIc approaches... ;-}
In fact, all it has are two circling approaches, VOR-A (GPS-A)
and VOR/DME (GPS-B), and those are only approved for planes which
land slower than 120 kts. But still...]

+---------------
| I am telling you, the software had plausibility checks.
+---------------

No argument. But I'm just saying that getting the plausibility checks
"right" isn't trivial. You'd need a database for each possible approach
type to each possible runway at each possible airport at which you might
attempt a landing. And then you'd have to debug the database... and then
keep it current with any new construction around each airport... etc.


-Rob

-----
Rob Warnock			<rpw3@rpw3.org>
627 26th Avenue			<URL:http://rpw3.org/>
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