Sandel 3308 HSI

[luvflyin]

A problem showed up in someones Sandel 3308. It had a Fluxgate failure and seems to have started "fast slaving," causing the compass card to swing erratically. A link was given to the Pilots Guide that had a Service Letter about Fluxgate failure. It says "The fluxgate is the only sensor which provides heading to the SN3308. The underline was from the Service Letter. Nowhere can I find what you do to inhibit the bad Fluxgate inputs and manually set the DG to magnetic heading. Did they design this thing to not be able to "set DG." Like get straight and level, look at magnetic compass, set DG, repeat every 20 minutes or so? What I have to compare it to is a King 55 slaved HSI. You can let it "slave" to the Fluxgate or you can manually set the DG heading if there is a reason to do so.

 

[denverpilot]

Don't think it has a gyro to base anything off of when that fails. Never seen any way to get it out of slaved mode, but if you find it, lemme know.

If you get that one figured out, help Sandel fix the one we're waiting on repairs on too, would ya? I need that thing for a checkride.

Heh.

 

[James331]

Many of them use the same remote gyro the king HSIs use, I have a SN3308, never had the problem, but I honestly don't know how to make it just go off the gyro ether....

Don't mean to be Capt. Obvious, but I'd give Sandell a call tomorrow, they could tell you

 

[luvflyin]

Many of them use the same remote gyro the king HSIs use, I have a SN3308, never had the problem, but I honestly don't know how to make it just go off the gyro ether....

Don't mean to be Capt. Obvious, but I'd give Sandell a call tomorrow, they could tell you

Yeah. I read that it can use a variety of Remote Gyros including the Mid Continent. Thats the one my K55 used. You have a SN3308. Is there a knob to twist that rotates the compass card (electronically of course)???

 

[denverpilot]

Sorry misspoke on the gyro. The gyro has nothing to slave to, and there's no mode that's "gyro only".

If it thinks the flux gate heading is off of what it thinks he gyro should be by far enough it goes into that "fast slew" mode seen at startup. That's the "spinning".

There's no gyro only mode selectable by the pilot.

You should see how much fun they are when they reboot at regular intervals in flight. LOL.

 

[James331]

Yeah. I read that it can use a variety of Remote Gyros including the Mid Continent. Thats the one my K55 used. You have a SN3308. Is there a knob to twist that rotates the compass card (electronically of course)???

No compass correction knob, just OBS (which I really don't use) and the heading bug, maybe something in the settings screen somewhere, I've never really dug into it to find it though.

 

[denverpilot]

No compass correction knob, just OBS (which I really don't use) and the heading bug, maybe something in the settings screen somewhere, I've never really dug into it to find it though.

Someone posted a link to the user manual in one of the other three threads of failing Sandels today. I had read the dead-tree version a while ago but I read their linked version again and I wasn't speaking from ignorance above. There is nothing in the setting screen or anywhere else to do it. If the flux gate fails, the unit is Tango Uniform if the thing doesn't recognize it as a failure. It'll just happily spin forever in fast slew mode and there's no "just use the gyro and let me set it" mode.

Man I'm glad all this expensive stuff is "certified". Makes me feel safer over using better and newer products at a third the price.

How about you? Hehehe.

 

[James331]

That does suck that you can't go straight gyro mode, and the FAA dragging their feet on getting the newer stuff into the fleet is annoying, that said I do like my 3308.

 

[bnt83]

I don't think any of the new gizmos will do a "gyro mode" either... If there is a flux detector error what's gonna be different? Something GPS derived?

 

[azure]

Yeah. I read that it can use a variety of Remote Gyros including the Mid Continent. Thats the one my K55 used. You have a SN3308. Is there a knob to twist that rotates the compass card (electronically of course)???

I believe there is, but it is only accessible in a special mode intended for use by avionics technicians. I vaguely recall my avionics guy adjusting mine several years ago. As far as I know there is no way for the pilot to adjust the compass card to compensate for slaving problems. Certainly there is nothing documented in the Sandel pilot's guide.

 

[luvflyin]

I'm still trying to get my head wrapped around this. Here's what I think I know. The 3308 has no internal "heading" mechanism, it must be driven from something external. Very common is a Remote Gyro like a Mid Continent Remote Directional Gyro. In many other HSI applications it can be either slaved or not slaved. If it is, it keeps up with precession issues and keeps the Gyro aligned with reference to magnetic north. It does this with a Fluxgate which is nothing more than a magnetic compass that has electrical outputs that can be processed and used to do stuff like keeping the Directional Gyro set to magnetic heading. If its not slaved then you set it yourself. You can push a button and select either slaved or not (presuming of course that it has the slaving feature to begin with.) But the Sandel 3308 has no way to do that. If the Fluxgate fails, you lose heading information. Even though the Gyro may still be working just fine, the 3308 starts having an electrical nervous breakdown and goes into "fast slaving," trying to slave to something that isn't there or is erratic and unreliable.

Reading more, it seems like there is a way to take the Gyro out of the loop and run the heading indicator(compass card) in the 3308 directly from the Fluxgate. But even though the Gyro is still out of the loop the 3308 still "dampens" the input from the Fluxgate limiting it to 3 degrees of change per minute. Doing that when the Fluxgate is keeping the Gyro magnetic makes sense, we only did it once about every 20 minutes or so the old fashioned way. Why not just let it straight through to the heading indicator if the gyro is out of the loop?
Hold the phone. Actually answer the phone.
Charlie from Sandel just returned my call. Letting the Fluxgate through in real time isn't good. They are notoriously noisey(electronically) and must be dampened and averaged out. The nature of the closed loop system that is necessary (I don't really get the details on this) make it unable to have heading manually put in by the pilot. There is a solution though, guys way up north like in Alaska do it. It's the King KCS305 and KA51B.

 

[James331]

Huh, I always wondered why mine had the KCS305 instead of the factory sandell solid state box, always thought it was just because the guy got a better deal in the king, don't have the KA51B however....

 

[denverpilot]

I'm still trying to get my head wrapped around this. Here's what I think I know. The 3308 has no internal "heading" mechanism, it must be driven from something external. Very common is a Remote Gyro like a Mid Continent Remote Directional Gyro. In many other HSI applications it can be either slaved or not slaved. If it is, it keeps up with precession issues and keeps the Gyro aligned with reference to magnetic north. It does this with a Fluxgate which is nothing more than a magnetic compass that has electrical outputs that can be processed and used to do stuff like keeping the Directional Gyro set to magnetic heading. If its not slaved then you set it yourself. You can push a button and select either slaved or not (presuming of course that it has the slaving feature to begin with.) But the Sandel 3308 has no way to do that. If the Fluxgate fails, you lose heading information. Even though the Gyro may still be working just fine, the 3308 starts having an electrical nervous breakdown and goes into "fast slaving," trying to slave to something that isn't there or is erratic and unreliable.

Reading more, it seems like there is a way to take the Gyro out of the loop and run the heading indicator(compass card) in the 3308 directly from the Fluxgate. But even though the Gyro is still out of the loop the 3308 still "dampens" the input from the Fluxgate limiting it to 3 degrees of change per minute. Doing that when the Fluxgate is keeping the Gyro magnetic makes sense, we only did it once about every 20 minutes or so the old fashioned way. Why not just let it straight through to the heading indicator if the gyro is out of the loop?
Hold the phone. Actually answer the phone.
Charlie from Sandel just returned my call. Letting the Fluxgate through in real time isn't good. They are notoriously noisey(electronically) and must be dampened and averaged out. The nature of the closed loop system that is necessary (I don't really get the details on this) make it unable to have heading manually put in by the pilot. There is a solution though, guys way up north like in Alaska do it. It's the King KCS305 and KA51B.

It's called, "Forgot to code in a way to run gyro-only and let the human do the updates for heading."

Wouldn't have been that difficult to add. Especially considering all of the other crap software modes one doesn't need to survive in IMC. Poor design.

I got a kick out of all of the waypoints in the thing not being able to be loaded from the GPS data. Wonder how many people stay up on those updates...

After seeing the available failure modes, I'd want a backup heading indicator more capable than a mag compass to fly behind if I owned one of these silly things.

And a backup OBS hooked to the ILS receiver or GPS via a switch because shooting an ILS with a spinning HSI would be just dandy fun.

Huh, I always wondered why mine had the KCS305 instead of the factory sandell solid state box, always thought it was just because the guy got a better deal in the king, don't have the KA51B however....

Yup. The More You Know... Haha.

It's a lovely primary instrument when it's working, but the failure modes are where it falls down and doesn't revert and can't be reverted to anything useful.

It already gets the rate of turn info from the gyro, all that's needed is a button to say "stop trying to slave and let me twist the knob to set a reasonable heading" and the failure mode would be much much better. No worse than a real DG that's precessing a bit, in that mode -- if it existed.

We all know how to fly with Mr. Whiskey Compass. That's not the issue. It's that the display could have been taught to be more a lot more useful if the flux gate crapped the bed by allowing the pilot to replace the flux gate in that information update loop.