Turn Coordinator or second attitude indicator?

[jetdriven]

Hey all.  I am gathering opinions on what to do. We have a standard 6 pack panel in our 1977 201, and the turn coordinator bearings are shot.  The vacuum AI is a little suspect too, perhaps less so since I turned the vacuum up.  

AC 91-75 from your friendly FAA says they now recommend replacing the turn coordinator with a second attitude indicator and a slip/skid ball.  They are expensive, however.  

So what would you do, overhaul or replace the turn coordinator, Replace it with a used AI?  Or something else?

[John Pleisse]

Did you get the Electric AI yet? I still have it...have not had time to mess with it. PM me if you still want it. I'll fill you in on it. It's a good unit. RC Allen 14v backlit.

[N33GG]

My personal preference:  Replace with new coordinator.  A cockpit just isn't the same without it.

[DaV8or]

Your AP OK? If not, maybe now's the time for an S-Tec. Otherwise, the AI gives you more information, so as long as it is electric and your other AI is vacuum, I might go that way. I think I might make the electric one primary and the vacuum one secondary. Any minute now somebody is going to come in here and say go for an Aspen!

[WardHolbrook]

Jetdriven,

Personally, unless you need the TC for the autopilot input, I'd go with the second AI. Let's face it, who needs a TC? They don't even install them in our jets and if you ever lost your primary AI, life is a whole lot less complicated with a backup AI instead of screwing around IFR with just N/B/A. At this point in our careers, easy and simple is always better. Even if you need a TC to drive the AP, you can always mount a blind TC and still get the safety backup of the 2nd AI. Like Dave said, you would want one to be vacuum and the other electric. 

Ward

 

[carusoam]

I think the turn coordinator may have gone the way of the ADF and Loran...A valuable tool that still works, but quite possibly has been surpassed.

Back in the day it was a nice gyro that could run on electricity and get you out of a tight spot in a pinch....and was a step up from the TNB.

The TC offers two things that the AI (directly) does not...  standard rate turn and inclinometer for coordination.

New back-up AIs have the inclinometer, and standard rate is a function of speed and bank angle.

What I don't like about the TC, is it's sensitivity.  I was bumping around in clouds the other day and realized that if I lose my AI, the TC does not seem like a real reliable source of information during constant turbulence.

If there is a sudden upset, it would be difficult to find where level is in heavy bumps.  The AI on the other hand was much more steady.

In modern times, I would vote for a back-up AI.  Does the Aspen have a simulated inclinometer?

Best regards,

-a-

[Bennett]

In the next several weeks I will be replacing my TC with a Mid-Century "Lifesaver" electic AI with inclinomer. What I like about this unit is that it has a back-up battery, either as a remote, or "piggyback".  The unit will show lights to indicate that it should be switched to battery power, and then confirm that this is the case.  Having lost two vacuum pumps in IMC, I am wary of vacuum systems. I do have a second vacuum pump which is electrically driven, and has a panel switch to operate (and check at every startup), but this is only valuable if the indicator head doesn't fail. In one case, debris from the failed pump caused damage to the indicator, which becaume unuseable, and it had to be repaired (read expensive) after I landed.  If you don't want the battery backup, I would recommend the Castleberry or SigmaTek units.  Considerably less expensive than the Mid-Continent "Lifesaver". 

[jetdriven]

The Century IIB A/P works from the vacuum ADI and the vacuum DG.   The TC does nothing unless you count saving your butt in IMC.

[robert14]

I replaced my TC with a Castleberry AI when I began my IFR training in my 65 M20E about a year ago. Works great. The only "issue" is making a standard rate turn without the rate indication. During slow flight, 90 mph, I use 17 deg (half-way between the 15 and 20 deg marks. For slow cruise/climb, 120 mph, I use the 20 deg bank mark for standard rate. For normal cruise, 150 mph, I use 22 deg, half-way between the 20 and 25 deg marks. I would not go back back to a TC for IFR.

[rob]

Quote: DaV8or

Your AP OK? If not, maybe now's the time for an S-Tec. Otherwise, the AI gives you more information, so as long as it is electric and your other AI is vacuum, I might go that way. I think I might make the electric one primary and the vacuum one secondary. Any minute now somebody is going to come in here and say go for an Aspen!

[rob]

Quote: carusoam

In modern times, I would vote for a back-up AI.  Does the Aspen have a simulated inclinometer?

Best regards,

-a-

[WardHolbrook]

Quote: jetdriven

...The TC does nothing unless you count saving your butt in IMC...

[jetdriven]

it is useful as a backup but doesnt directly read pitch or bank. 

[WardHolbrook]

 

One can only base their informed opinions upon their personal experience. I have 4000 hours in aircraft that had TCs/T&Bs and 11,000+ hours in aircraft that have 3 AIs and no TCs. I have also given several hundred hours of instrument dual and many ICCs over the past 35 or so years. Finally, I have had two total vacuum failures while in solid IFR conditions that resulted in me having to hand-fly N/B/A for an extended period of time. Having a vacuum/pressure pump failure is only a matter of time - dry pumps have a MTBF of what? 600 hours of so? Wet pumps will do a bit better, but they don't last forever either.

Based upon my personal experience and based upon my experience as a CFII I can say that most folks don’t do very well using N/B/A because they don’t practice it enough to maintain proficiency with it. For this simple reason alone, I strongly recommend the installation of a 2^nd AI - unless you regularly cover up both the AI and HI and spend some quality time flying N/B/A. It’s a matter of discipline and most folks simply don’t do it enough to be proficient with it. When a gyro fails or your vacuum source(s) decides to go south on you that's probably not the best time to be trying to renew long lost skills. On the other hand, most of us do tend to spend significant amounts of time staring at an AI, so in the event of a primary AI failure, it’s just a matter of adjusting your scan when the inevitable happens. Not a big deal either way.

As for standard rate turns without a turn rate indicator, in a light plane, just take airspeed, drop the last digit, and add 7 to get bank angle for standard rate (or close enough for that purpose), e.g., 120 knots, drop zero to get 12, add 7 to get 19 degrees bank for standard rate.

That's my reasoning for the opinion that I have, but as always, it's just my opinion and your mileage may vary.

 

[Jerry 5TJ]

I put a second AI in my Mooney, and kept the TC.  If you have two gyros, which do you believe if they disagree?  With three sources of roll information, you can determine which device has failed more quickly.  

 

[jetdriven]

If two bank indications differ,  use the compass to break the tie.

[DaV8or]

Quote: jetdriven

If two bank indications differ,  use the compass to break the tie.

[tony]

For you guys who took your turn coordinator out, what did you do with the PC?

[Wistarmo]

I did like Jerry.  In my last two aircraft, I removed the ADF and replaced it with a backup electric attitude indicator.  I have been very happy with this arrangement.

[FloridaMan]

I lost a vacuum pump in clear VFR when I had less than 200 hours. The airplane I was flying was also equipped with an electric backup pump that also failed. It wasn't like when you're doing your instrument training and your instructor slaps a post-it over the indicator, it slowly rotated in a manner that you might chase to put yourself in a bad situation. If you have two and one fails, I imagine the electric would give you a flag and the vacuum operated one would most likely be the result of a pump failure, which would be indicated by the gauge.

This is what my failure looked like:

I would not be comfortable bouncing around in Florida IMC using the turn coordinator to keep my wings level.

[carusoam]

Antares,

 

Did the DG fail rotating in the opposite direction?

 

In the video, it seems to be inop already.

 

Classic IFR training indicates that vac failure has the DG fail indicating a turn in the opposite direction of the failing AI.  I have not witnessed a real failure to test the accuracy of this statement.

 

Modern Mooneys add a warning light in the annunciator panel to help identify the low or high vac problem.

 

Best regards,

 

-a-

[Jerry 5TJ]

...and in the Mirage we have two vacuum AIs, and one electric AI, and two electric TCs.  There are two vacuum pumps, and two alternators, too.   I guess I am a 'belt and suspenders' kinda guy when it comes to IMC. 

[RJBrown]

 I like having a TC. I would not choose to lose the standard rate turn indication of the TC.  If you find yourself in an unusual attitude it is great to just pull the power, stomp on the ball to level the wings of the TC and pull out gradually. This is an ingrained reaction. NO real thought or interpretation needed. A spinning AI is hard to interpret versus a ball to the side. I would not replace the this function with a glass panel version.  If I were to add the second AI I would leave the TC alone. Putting the second IA on the level with and to the right of the original. In my plane it would force moving the intercom to the right. The top right position would also be most useful for a right seat pilot. Bottom left is not a good place for the backup.

This brings up in my mind the stupidity Mooney showed in placing the "three death balls" on the right edge of the panel in the G1000 installation. Placing them there may have filled the regulatory need for back ups but did so in the most useless manner.

[Bennett]

The Mid-Continent "Life-Saver" electric AI with battery back-up has an optional "slip indicator", which has a ball in a clear tube.  This arrangemant is a legal substritute for a TC.  Doesn't look like a kludge, or improvised add on, and will give you the information to keep your turns coordinated.

[jetdriven]

If your attitude indicator is "spinning" you are almost certainly finished.  I think a second AI will prevent you begin in that situation in the first place.   Also, the second AI must have a slip/skid ball mounted on it or immediately below it to be legal per the AC.