If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Backup gyros - which do you trust?
There are several things you can add to help with the identification, In my
plane I have a low vacuum warning light (part of the precise flight backup) mounted between the AI and DG. The AI is one of the sigmatec ones with a vacuum flag, so that if vacuum is lost in the instrument but not in the system I still know about it right away. These warnings cover identification of the more common cause of loss of the AI. The other failure mode would be failure of the gyro, in which case I don't believe you get the insidious gradual spin-down like you do with loss of vacuum. I also fly with the GPS on the HSI page to offer yet another source of redundancy. Personally, I think the instrument scan typically taught relies too heavily on the AI given its relatively low reliability. Unfortunately, the alternative is a scan that works a bit more like a partial panel scan using the AI as supporting, not primary. Such a scan is much harder to master and requires considerable finesse to keep from chasing the needles. It is not one I would expect to be able to teach someone just learning to fly by instruments. -- --Ray Andraka, P.E. President, the Andraka Consulting Group, Inc. 401/884-7930 Fax 401/884-7950 http://www.andraka.com "They that give up essential liberty to obtain a little temporary safety deserve neither liberty nor safety." -Benjamin Franklin, 1759 |
#2
|
|||
|
|||
You have three sources of bank information in a typical panel: the attitude
indicator, the turn coordinator, and the heading indicator. If two agree and the third does not, it is faulty. Add a fourth source and it makes elimination that much easier. Bob Gardner "Steve House" wrote in message ... I've been reading with interest the several threads where a number of people have strongly pointed out the advantages of a backup electric AI to supplant a vacum driven main AI. But I'm reminded of the saying "A man with a good watch always knows what time it is. A man with two watches is never sure." So I'm toodling along in IMC with no outside horizon reference and I see my two AIs don't agree with each other. How do I determine which to trust? If I had a third, I could go with a 2 of 3 voting strategy of course, but with only two, what do you do to decide which is operating properly and which one has faulted? Obviously I can look for consistency with other instruments - does my DG or Turn indicator show I'm turning, does the VSI show a climb or descent - but what would be the best strategy given the various ways vacuum or electric driven instruments can fail? |
#3
|
|||
|
|||
Bob Gardner wrote:
You have three sources of bank information in a typical panel: the attitude indicator, the turn coordinator, and the heading indicator. Um, isn't this leaving out something fundamental (and pretty reliable, if difficult to interpret)? Sydney (Be Expert With Map and Compass) |
#4
|
|||
|
|||
The presence of two attitude indicators is especially valuable when they
disagree. That disagreement will direct your attention to the needle/ball and basic flight instruments to help determine which one is correct. With a single AI you could more easily follow a gyro error without noticing a difference in the other basic instruments until it was too late. -- Darrell R. Schmidt B-58 Hustler History: http://members.cox.net/dschmidt1/ "Steve House" wrote in message ... I've been reading with interest the several threads where a number of people have strongly pointed out the advantages of a backup electric AI to supplant a vacum driven main AI. But I'm reminded of the saying "A man with a good watch always knows what time it is. A man with two watches is never sure." So I'm toodling along in IMC with no outside horizon reference and I see my two AIs don't agree with each other. How do I determine which to trust? If I had a third, I could go with a 2 of 3 voting strategy of course, but with only two, what do you do to decide which is operating properly and which one has faulted? Obviously I can look for consistency with other instruments - does my DG or Turn indicator show I'm turning, does the VSI show a climb or descent - but what would be the best strategy given the various ways vacuum or electric driven instruments can fail? |
#5
|
|||
|
|||
Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning
lights on the annunciator panel. If I had an electric AI and a vacuum AI and they disagreed markedly, I would be suspicious of the one having warning lights and flags all over it. Otherwise, comparing them to the other instruments, as you suggested, is the best approach. AOPA Safety Foundation just ran some tests on how long it takes a pilot to recognize that his vacuum system has failed, and how long it takes pilots to recover from those failures. Many times it took over 90 seconds, which is way too long. Some never did recognize the failure. However, none of them were convinced that the vacuum instruments were working and that it was the other instruments that had failed. IIRC somewhat less than half discovered the problem quickly and took quick action. Only about 1/4 of them covered the failed instrument. |
#6
|
|||
|
|||
C J Campbell wrote:
Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning lights on the annunciator panel. If I had an electric AI and a vacuum AI and they disagreed markedly, I would be suspicious of the one having warning lights and flags all over it. CJ, How do newer vacuum AIs come with dual vacuum pumps? We have a "warning flag" on our newer AI. I note that it is really a low vacuum flag. It doesn't say a thing about how reliably the instrument itself is operating. Sydney |
#7
|
|||
|
|||
"Sydney Hoeltzli" wrote in message ... | C J Campbell wrote: | Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning | lights on the annunciator panel. If I had an electric AI and a vacuum AI and | they disagreed markedly, I would be suspicious of the one having warning | lights and flags all over it. | | CJ, | | How do newer vacuum AIs come with dual vacuum pumps? | They come with a new airplane attached to them. Not unlike the $350,000 Cessna ball cap I bought. |
#8
|
|||
|
|||
Sydney Hoeltzli writes:
We have a "warning flag" on our newer AI. I note that it is really a low vacuum flag. It doesn't say a thing about how reliably the instrument itself is operating. Yup, I had one freeze but the vacuum was fine so it didn't complain. --kyler |
#9
|
|||
|
|||
C J Campbell wrote: Newer vacuum AIs have warning flags, dual vacuum pumps, and vacuum warning lights on the annunciator panel. If I had an electric AI and a vacuum AI and they disagreed markedly, I would be suspicious of the one having warning lights and flags all over it. I just bought a new AI this spring. For an extra $50 or so you can get the one with the flag. Since I already have the EI volts/amps instrument that has warning lights for both high and low voltage, but no warning light for the vacuum pump, I spent a little extra for the flag. Now I don't need a suction warning lamp. |
#10
|
|||
|
|||
Ray Andraka wrote:
Personally, I think the instrument scan typically taught relies too heavily on the AI given its relatively low reliability. Unfortunately, the alternative is a scan that works a bit more like a partial panel scan using the AI as supporting, not primary. Such a scan is much harder to master and requires considerable finesse to keep from chasing the needles. It is not one I would expect to be able to teach someone just learning to fly by instruments. You are probably right. When I did my initial IFR training, my instructor was very big on partial panel work. As a result, I learned to not rely on the AI, and I find partial panel approaches (in training, anyway) almost a non-event. The downside, is that I suspect I don't use the information the AI gives me as much as I should. I tend to fly pitch by airspeed, not by the AI. This probably makes me not as smooth and precise as I might otherwise be. But I do have a lot of confidence that I can fly an approach on the TC and ASI alone. |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Good AI backup, wish me luck | Robert M. Gary | Instrument Flight Rules | 29 | March 1st 04 05:36 PM |
Solid State Backup AI | Dan Truesdell | Instrument Flight Rules | 20 | January 15th 04 09:53 PM |
Gyros - which do you trust? | Julian Scarfe | Instrument Flight Rules | 6 | July 27th 03 09:36 AM |
Backup gyros - which do you trust? | Dan Luke | Owning | 46 | July 17th 03 08:06 PM |
Backup gyros - which do you trust? | Dan Luke | Piloting | 23 | July 17th 03 08:06 PM |