Emergency instrument approaches using 430/420

I would be interested in the forum’s collective perspectives on using the 430/420 and its map to get down in an emergency under low-medium IFR contitions: engine out, passenger or pilot medical, ILS LOC/glideslope failure, etc. I have thought this through for my 260se: trim for 60-65 KIAS, fly a “normal” pattern, subtract half the runway length from the “direct-to airport” distance to judge approximate distance from the threshold, and multiply groundspeed by 5 to get a ~3 degree descent or ~6 for a 4 degree descent. At my slow approach speed I can be a little slack about needing to touch down just after the threshold…the SR20 shouldn’t be too different, maybe an extra 15 kt approach speed.

Thoughts?

In an emergency whatever works, works. I guess the question is, will it work?

As far as IFR engine out, it sounds like a reasonable last resort procedure, with the following understandings (and I’m sure you’ve thought of them already):

  • The airport waypoint will not necessairily correspond to a runway centerline, so even if everything works perfectly you might not be lined up when you break out. (This assumes an airport with no IAP; otherwise you could call the IAP up from the GPS if you could find one that corresponds to your inbound course.)

  • Of course, if there are any obstacles in the area (terrain, towers, other aircraft, etc.) the procedure will not ensure that you clear them.

In any scenario other than engine out, you’d have to weigh the cost of delay against the risk of the “homebrew” approach.

All that said, any forethought about what you’d do in an emegrency situation is valuable! I’m sure having thought about things like descent rates, airspeeds, etc., in advance will pay off when they’re needed in the heat of battle.

Joe

I would be interested in the forum’s collective perspectives on using the 430/420 and its map to get down in an emergency under low-medium IFR contitions: engine out, passenger or pilot medical, ILS LOC/glideslope failure, etc. I have thought this through for my 260se: trim for 60-65 KIAS, fly a “normal” pattern, subtract half the runway length from the “direct-to airport” distance to judge approximate distance from the threshold, and multiply groundspeed by 5 to get a ~3 degree descent or ~6 for a 4 degree descent. At my slow approach speed I can be a little slack about needing to touch down just after the threshold…the SR20 shouldn’t be too different, maybe an extra 15 kt approach speed.

Thoughts?

Kevin,

I didn’t understand your comments about multiplying ground speed by 5 to get a 3 degree descent or 6 for a 4 degree descent. Would you clarify, if only for me?

Thanks,

Bill

  • The airport waypoint will not necessairily correspond to a runway centerline, so even if everything works perfectly you might not be lined up when you break out. (This assumes an airport with no IAP; otherwise you could call the IAP up from the GPS if you could find one that corresponds to your inbound course.)

You’re quite right about this, but the GNS430’s map shows the runway layouts and locations. You can set the map to very low range (3500 feet? 1 mile?) and see the runways well enough to fly a pattern and/or line up on final. I tried it out at a poorly used field and was encouraged by the results. Thus you could use the distance-to-waypoint as just a distance reference.

  • Of course, if there are any obstacles in the area (terrain, towers, other aircraft, etc.) the procedure will not ensure that you clear them.

I hope at most airports that flying a “short approach” profile in the normal traffic pattern would ensure obstacle clearance. Maybe I’m wrong but I suppose it’s the risk that one would have to take with so few cards left in the hand!

To get a 3 degree descent gradient, multiply your groundspeed in kt by 5 to get required fpm down, e.g., for 100 kt, you want ~500 fpm descent to maintain a 3 degree glideslope. It’s not exact but works quite well. Multiplying by 6 or 7 for a 4 degree gradient is less accurate (more like 3.6 degrees or 4.3 degrees respectively) but pretty close. Try it out next time you’re on an ILS!

Sorry to have been so terse about it as to be obtuse!

Kevin