Thoughts on backup AI

[tonycondon]

On a related note, I was flying with Chris Jones today in his RV. Its an all electric airplane with a Dynon EFIS for main display, Airspeed, Altimeter, TC, Compass, and VS for backup. Garmin 430 is all he has for Nav/Comm. I simulated a total electrical failure by dimming down all the displays, TC covered up, autopilot off. He flew a decent approach using the 396 "5 pack" and building the approach in the handheld using the waypoints. Legal for IFR? no. Save your butt? youbetcha.

 

[poadeleted20]

On a related note, I was flying with Chris Jones today in his RV. Its an all electric airplane with a Dynon EFIS for main display, Airspeed, Altimeter, TC, Compass, and VS for backup. Garmin 430 is all he has for Nav/Comm. I simulated a total electrical failure by dimming down all the displays, TC covered up, autopilot off. He flew a decent approach using the 396 "5 pack" and building the approach in the handheld using the waypoints. Legal for IFR? no.

After a total electrical failure? You bet it's legal -- 91.3(b) gives lese majesty for deviation from any/all 91.205 equipment requirements "to the extent required to meet that emergency." Just don't take off IFR that way.

BTW, in an experiment suggested by discussion on the red board, I tried flying my ATC-610J simulator with the AI and the turn rate portion of the TC (but not the ball) covered to simulate an unusual failure mode -- and had no problem doing it. I was pretty cautious with turn rates, but was able to judge bank angle by the speed at which the heading indicator ("DG") was turning -- essentially an undifferentiated version of turn rate as measured by the TC's turn rate indicator. I'm not suggesting this as a good alternative to a backup AI, but it's nice to know that if the AI and TC both die, you can (well, I can -- you'd have to try it yourself to see if you can, preferably under the hood with a CFI-IA riding shotgun or in a sim -- better to do it the first time not for real) get by on DG, ball, airspeed, and altimeter as long as you're gentle about it.

 

[tonycondon]

good point Ron, like I was telling Chris, this is an oh **** theres no other way out type of procedure. If you cant get to VFR, no holes, basically the flying gods are trying to smite you. I guess in technical terms i was saying it is a 91.3 type of situation.

 

[gismo]

Good points, Lance. Thanks. My JPI will start flashing in a low voltage situation, and I bought a new Concord sealed battery just last year. It is my hope and expectation that that will be enough to get me on the ground or into VMC.

It needn't be based on hope. If you set the low voltage threshold between the normal bus voltage and the open circuit voltage of the battery (13 or 26 volts is a good setting) and set the alarm delay to no more than a minute, you will get a warning before any appreciable energy is lost. For the next step it helps to have an ammeter rather than a loadmeter since the latter will be reading zero when the alternator goes offline. If you reduce the discharge to less than half the AH rating of your battery you should be good for well over an hour. If you don't have an ammeter, you can experiment with various loads when the alternator is working to see what it takes in load shedding to get down to that level of discharge.

 

[Bill]

He flew a decent approach using the 396 "5 pack" and building the approach in the handheld using the waypoints. Legal for IFR? no. Save your butt? youbetcha.

Thanks, Tony, once we're setup, I'll grab my CFII and do some x96 practice apps.

 

[jhempel]

Where does the 396 get pitch information?

 

[tonycondon]

it doesnt. the 5 pack includes track, altitude, vertical speed, turn rate, and groundspeed.

 

[jhempel]

it doesnt. the 5 pack includes track, altitude, vertical speed, turn rate, and groundspeed.

Thank you. That is what I thought. I figured that it just knows the point in space where it is and what direction that point is moving. I didn't see any way it would know the pitch / yaw of the plane.