Saturday, April 16, 2005

Gizmos Gone Gonzo



Technology is great, when it works. My airplane has a ton of gee-whiz electronics to play with, a rather impressive array for a regional turboprop. It features an all-glass cockpit ("fly by watching TV!") with the latest and greatest in situational awareness. We have two very capable flight management systems in the airplane, which is rare for regional airlines in the US - most have an FMS for the captain only. We have a state of the art navigation system that lets us shoot precise GPS approaches with lateral and vertical guidance (LNAV/VNAV) without any ground-based navaids. Significantly, we have Cat III approach capability that lets us land with only 600 feet visibility. Usually Cat III approaches can only be done by a capable multi-channel autopilot with autoland features. Amazingly, we hand-fly ours - by use of a military-style Heads-up Guidance System (HGS).

The captain flies the approach while looking out the window, instead of looking down at the instrument panel. He looks through a clear glass plate, onto which is projected a display of aircraft attitude, airspeed, altitude, etc. A small pointer serves as an "intertia vector," showing where the plane is headed at any particular moment. A circle moves to show where the airplane should be heading to stay on the approach path. Keep the pointer in the circle, and voila! Precision, hand-flown Cat III approach in insanely crappy weather (600 ft is covered in under 3 seconds at our approach speeds). We're even certified for single-engine Cat III approaches - no other regional can do them.

Okay, so that's assuming everything works. What's really maddening is that it often won't, for no apparent reason. The HGS is programmed to not arm itself for Cat III if everything isn't set up perfectly, but it sometimes seems to think you've messed up even through you know everything is in order. Today we were flying into Seattle, and even though the weather was well above Cat I minimums (200 ft ceiling and 1800 ft visibility), the captain wanted to practice Cat III procedures. So I checked and double-checked that everything was set up, we ran the appropriate checklists - and it didn't arm! We reset the system a few times to no avail. This has happened to me several times before, fortunately always in decent weather. There are many foggy Northwest winter days, however, when we need the Cat III capability, and the HGS puking then could leave a crew with a poor choice: divert to the alternate - or cut into fuel supply on subsequent attempts, hoping the system finally decides you've set everything up right. (Note to future Captain Sam: Adding extra fuel on foggy days is a good idea!)

When my airline was first doing FMS approaches, they had a heck of a time with those, too. The FMS would wait until you were in the middle of the approach to decide it wasn't absolutely sure that it knew it's position, and would kick you back into enroute mode. Software upgrades have mostly fixed the problem, but everyone keeps a close eye on them when shooting FMS approaches. Whenever possible we just shoot the ILS.

So yes, my airplane has lots of electronic wizardry on board, but you know what? At Ameriflight I fly 1970's-era Chieftains with original analog avionics and they do quite alright. You'll never ask "what's it doing?" in the Chieftain so long as you know what you're doing. Plus, you never have to fly when it's so foggy that the birds are grounded.

1 Comments:

Blogger Greg Raiz said...

Sam, this photo of your plane is really cool. I would like to use it in an iPhone project I'm working on. Would that be OK? If so can you contact me at graiz at raizlabs dot com.

12:45 PM  

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