slow attitude indicator

fredh · #1 10-17-09, 10:50 AM

I have a de-iced 73 P model and have a slow to spool up attitude indicator. Looking through the service manual it seems the de-iced versions vacuum system is different from the non de-iced a/c , I was thinking maybe I have a plugged or restricted vacuum filter but can't find it and am thinking it may not have an inline filter. I found both garter filters but no inline filter. Thanks in advance for the assistance.
Fred II

Guy Paris · #2 10-17-09, 02:38 PM

Fred,
How long has it been since the A/I was overhauled? Do you have the vaccum indicator and is it reading in the normal range? Do you have another vacuum A/I and if so how does it compare. Just some thoughts. guy paris

fredh · #3 10-17-09, 07:39 PM

Thank you both for your replies. I will try the alternate static source next time. I'm not sure when the last overhaul was, that is likely what need to happen. The A/I has not been touched in the 5 years I have owned the a/c. I was just thinking it may be a filter. As for the vacuum indicator it shows fine and I don't have another A/I for comparison.

skymstr02 · #4 10-17-09, 08:18 PM

Is the DG precessing more than usual? Both instruments use the same filter element.

Disregard if you have a slaved HSI.

fredh · #5 10-17-09, 08:39 PM

Slaved HSI, but thank you

tropical · #6 10-18-09, 11:57 AM

Quote:

Originally Posted by hharney

Fred
Did you try the alternate static source to see if that changed the reaction time?

Since when does the static system have anything to do with the vacuum system?

hharney · #7 10-18-09, 12:42 PM

It doesn't, just misread the post. Thought he was talking altimeter. My bad

Dave Underwood · #8 10-18-09, 12:47 PM

On my 1978 P, there is only minor difference between boots and no boots.

In the past I have suffered a slow DG, even though slaved. A no-gyro vectored approach and reasonable ceiling made it a non-event.

It turned out to be a crack in the thin, semi-clear hoses that run from the shuttle valve above the P2 rudder pedals individually to the two instruments. The hoses are 20 + years old. There are four lines, two to the instruments and two smaller to run the dolls eyes on the vac. gauge if memory serves me right. BTW, even with the cracked hose, I had good vacum indicated and both dolls eyes were in as I am pretty sure the vac gauge takes its readings from the join on the inlet side on the far left of the P1, just before the hoses disappear downwards.

On the right hand side hose on the instrument side of the shuttle valve about 3" up, there is a T which connects to the boots and draws them down and if I remember correctly, that is controlled by a timer valve on the P2 side, on the firewall. My manual is not here, but I think that is correct.

The tubing on mine has actually cracked several times in the past based on various repairs. I am in the process of replacing all the hoses with thin walled rubber of the appropriate specification as the existing tubing is now quite brittle.

My suggestion would be to check the vacum to the AI and check the hoses for cracks. If you disconnect the AI and block the end where is attaches to the AI, you might be able to hear any leakage.

Most instrument shops will do an IRAN on your instrument which is cheaper than replacing it.

Hope this helps.

Blue Skies = Dave