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Turn Coordinator Gyro
Hey,
I have what might be a dumb question, but I'm OK with asking it. :cool: I went to fly a coworkers airplane today, a 1979 Cessna 172N (I have flown it many times), and when I flipped the master switch as part of my preflight inspection (fuel guages, nav/beacon lights, flaps, etc), I heard complete silence. The electric gyro in the turn coorindator never spun up. I never noticed if the red flag indicating a failure/power was on or not. If I remember right, this is not a required piece of equipment for a daytime VFR flight. I let my mind wonder, and started thinking; was this an electrical problem in the turn coordinator, or was the problem further upstream? I didn't want to take off anyway and end up with an electrical system failure/fire due to a short somewhere. My question is, did I let my mind get the best of me, or did I make a smart decision? |
Did you check to see what the power source for that instrument was? Not all are electric. Did you check to see if a circuit breaker was out?
I can't speak for UK regulation, but generally speaking, if it's installed, it's got to work. If it doesn't work, it needs to be deactivated and placarded inoperative, so long as it's not required for the kind of operation in use (daytime, VFR, for example). |
Some gyros can be remarkably quiet. A quick taxi check and a few turns on the ground would have indicated whether working.
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It is definitely electrically powered, and I didn't see any breakers that were tripped. And I've flown this plane before, and it is definitely easy to hear (at least before...)
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This plane's turn coordinator is definitely electrically powered. I've flown it many times, and its noise is definitely noticeable.
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If a Cessna 172N has a factory original turn co-ordinator, it's electric. If it has a little red flag, it's electric. Those Turn co-ordinators are notoriously unreliable. They are DC electric, which means they have brushes which run on a commutator. The brushes wear, and the electricity stops flowing. Add to that, a commonly huge mess of greasy carbon inside. The red flag is not a 100% indicator of this failure. Listening is better, until you're in flight.
I have, and recommend to anyone who's going to keep the plane, to have the maintenance shop carefully remove it, and discard it with predjudice. Then, go and buy an AC version (which could run $1000) of the same instrument. You pay in the beginning, but it will very likely outlast the plane, with zero maintenance ever, and 100% reliability forever. Or, if you're thinking auto pilot, now's the time, as some come with a replacement turn co-ordinator. Though tempting, it would actually not be permitted to replace the electric turn co-ordinator with the older and more reliable vacuum turn and bank. This is because the of the design requirement for that aircraft that the turn indicator not be powered from the same power source as the attitude indicator - just in case one quits. Oh yeah, you know about that now! The vacuum pumps are a little more reliable that the factory original turn co-ordinators, but not much! It's always a smart decision to consider the unknown causes of electrical problems, and not fly, if in doubt. My experience would have allowed me to continue the flight, as long as everything else was working properly. If one of those quits, my experience is 99.9% instrument (totally benign to the rest of the aircraft), 0.1% upstream problem (and that will be detectable by observing other things wrong/breaker popped etc.), probably still benign to the aircraft, but worthy of consideration. |
Just noticed you're from Texas, ajstoner. That being the case, your original question seemed to pertain to whether or not the turn coordinator was a required item, as well as whether or not the turn coordinator had a problem.
Without actually being able to see the airplane in question, it's impossible to diagnose your turn coordinator problem. It could be the instrument, a circuit breaker, a loose cannon plug, or perhaps an additional power switch for the turn coordinator on the panel (some aircraft use them to prevent the turn coordinator from running when it's not needed). The day VFR instrumentation and equipment requirement to which you referred is found in 91.205: § 91.205 Powered civil aircraft with standard category U.S. airworthiness certificates: Instrument and equipment requirements. (a) General. Except as provided in paragraphs (c)(3) and (e) of this section, no person may operate a powered civil aircraft with a standard category U.S. airworthiness certificate in any operation described in paragraphs (b) through (f) of this section unless that aircraft contains the instruments and equipment specified in those paragraphs (or FAA-approved equivalents) for that type of operation, and those instruments and items of equipment are in operable condition. (b) Visual-flight rules (day). For VFR flight during the day, the following instruments and equipment are required: (1) Airspeed indicator. (2) Altimeter. (3) Magnetic direction indicator. (4) Tachometer for each engine. (5) Oil pressure gauge for each engine using pressure system. (6) Temperature gauge for each liquid-cooled engine. (7) Oil temperature gauge for each air-cooled engine. (8) Manifold pressure gauge for each altitude engine. (9) Fuel gauge indicating the quantity of fuel in each tank. (10) Landing gear position indicator, if the aircraft has a retractable landing gear. (11) For small civil airplanes certificated after March 11, 1996, in accordance with part 23 of this chapter, an approved aviation red or aviation white anticollision light system. In the event of failure of any light of the anticollision light system, operation of the aircraft may continue to a location where repairs or replacement can be made. (12) If the aircraft is operated for hire over water and beyond power-off gliding distance from shore, approved flotation gear readily available to each occupant and, unless the aircraft is operating under part 121 of this subchapter, at least one pyrotechnic signaling device. As used in this section, “shore” means that area of the land adjacent to the water which is above the high water mark and excludes land areas which are intermittently under water. (13) An approved safety belt with an approved metal-to-metal latching device for each occupant 2 years of age or older. (14) For small civil airplanes manufactured after July 18, 1978, an approved shoulder harness for each front seat. The shoulder harness must be designed to protect the occupant from serious head injury when the occupant experiences the ultimate inertia forces specified in §23.561(b)(2) of this chapter. Each shoulder harness installed at a flight crewmember station must permit the crewmember, when seated and with the safety belt and shoulder harness fastened, to perform all functions necessary for flight operations. For purposes of this paragraph— (i) The date of manufacture of an airplane is the date the inspection acceptance records reflect that the airplane is complete and meets the FAA-approved type design data; and (ii) A front seat is a seat located at a flight crewmember station or any seat located alongside such a seat. (15) An emergency locator transmitter, if required by §91.207. (16) For normal, utility, and acrobatic category airplanes with a seating configuration, excluding pilot seats, of 9 or less, manufactured after December 12, 1986, a shoulder harness for— (i) Each front seat that meets the requirements of §23.785 (g) and (h) of this chapter in effect on December 12, 1985; (ii) Each additional seat that meets the requirements of §23.785(g) of this chapter in effect on December 12, 1985. (17) For rotorcraft manufactured after September 16, 1992, a shoulder harness for each seat that meets the requirements of §27.2 or §29.2 of this chapter in effect on September 16, 1991. § 91.213 Inoperative instruments and equipment. (a) Except as provided in paragraph (d) of this section, no person may take off an aircraft with inoperative instruments or equipment installed unless the following conditions are met: The second choice is removal or deactivation. This is the more common method in light, private airplanes. The third option is to obtain a special flight permit, sometimes called a "ferry permit." § 91.213 Inoperative instruments and equipment. (d) Except for operations conducted in accordance with paragraph (a) or (c) of this section, a person may takeoff an aircraft in operations conducted under this part with inoperative instruments and equipment without an approved Minimum Equipment List provided— (1) The flight operation is conducted in a— (i) Rotorcraft, non-turbine-powered airplane, glider, lighter-than-air aircraft, powered parachute, or weight-shift-control aircraft, for which a master minimum equipment list has not been developed; or (ii) Small rotorcraft, nonturbine-powered small airplane, glider, or lighter-than-air aircraft for which a Master Minimum Equipment List has been developed; and (2) The inoperative instruments and equipment are not— (i) Part of the VFR-day type certification instruments and equipment prescribed in the applicable airworthiness regulations under which the aircraft was type certificated; (ii) Indicated as required on the aircraft's equipment list, or on the Kinds of Operations Equipment List for the kind of flight operation being conducted; (iii) Required by §91.205 or any other rule of this part for the specific kind of flight operation being conducted; or (iv) Required to be operational by an airworthiness directive; and (3) The inoperative instruments and equipment are— (i) Removed from the aircraft, the cockpit control placarded, and the maintenance recorded in accordance with §43.9 of this chapter; or (ii) Deactivated and placarded “Inoperative.” If deactivation of the inoperative instrument or equipment involves maintenance, it must be accomplished and recorded in accordance with part 43 of this chapter; and (4) A determination is made by a pilot, who is certificated and appropriately rated under part 61 of this chapter, or by a person, who is certificated and appropriately rated to perform maintenance on the aircraft, that the inoperative instrument or equipment does not constitute a hazard to the aircraft. An aircraft with inoperative instruments or equipment as provided in paragraph (d) of this section is considered to be in a properly altered condition acceptable to the Administrator. |
It's probably the brushes have gone, send it off for repair.
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That may be, but I'd second the suggestion by Pilot DAR. If one is going to spend the money to overhaul anyway, go with the upgrade and don't worry about it again.
Conversely, for one who might decide to operate as is, a simple short can turn into a fire or cause other problems. I worked for a corporate flight department some years ago as a copilot and director of maintenance. In addition to the corporate aircraft, several of the board of directors shared a Cherokee, which was also my responsibility. The TC wasn't working. I discovered that it had a wiring issue, not the least of which was that the wiring bundles were binding on the controls. While a fire was a possibility at the time, it wasn't nearly a concern that the binding controls were. I ended up re-routing wiring, moving instruments, and tying everything off. It came out well...but the point is that a small problem may be indicative of something unseen. If the instrument is going to be replaced or repaired, consider going with a better instrument. Dick Collins, formerly of Flying Magazine, championed replacing turn coordinators and turn and bank indicators with a second attitude gyro. This makes a lot of sense and provides a lot more useful information. |
championed replacing turn coordinators and turn and bank indicators with a second attitude gyro. This makes a lot of sense and provides a lot more useful information I'd stick with the configuration which Cessna offered from the factory, when it comes to primary flight instruments.... |
Thanks for all the information! I was always hesitant about the inop equipment (if it wasn't required for that type of flight) just because of that deactivation/removal part.
Is the turn coordinator something a pilot can deactivate without alot of effort? I don't remember seeing a breaker called out for it. |
Well, that's a bit tricky, and subject to some interpretation.
In Canada, the closest I can find to this would be in the list of tasks a pilot may carry out (does not require a maintenance person): (27) deactivating or securing inoperative systems in accordance with sections 605.09 or 605.10 of the CARs, including the installation of devices specifically intended for system deactivation, where the work does not involve disassembly, the installation of parts, or testing other than operational checks; Cessnas of this type did not leave the factory with circuit breakers you could pull. The earlier Cessnas had fuses, but often the circuits were joined, so that you'd loose several systems by removing one fuse. So, personally, I would be comfortable removing the cannon plug from the back of the turn co-ordinator, TYING IT PROPERLY OUT OF THE WAY, AND CONFIRMING THAT NOTHING IS FOULING BACK THERE! then marking the face of the instrument "inoperative" and flying within the suitably appropriate day VFR limits for the aircraft and pilot skill. That said, that's me. You have to do only what YOU are comfortable with, and within FAA regs, not Canada's. It is possible that you could be asked to justify what you had done - satisfy yourself you could! |
Pilot DAR
Richard Collins did NOT advocate removing the turn and slip, what he did advocate was replacing the traditional instrument with a second AI AND installing a 2 inch turn and bank somewhere else in the panel. Without a turn and slip the aircraft would NOT be IMC legal (IFR in IMC), but might be legal under VFR (see posts above). You are therefore correct, you need at least a means of keeping the ball in the pot. With glass sytems the ball is often combined with the backup AI which works just fine. Richard Collins was however correct. Relying on one AI (particularly if vac powered) is daft - however good our instrument flying skills, it is no fun completing the mission with just a turn and slip. This makes a lot of sense and provides a lot more useful information. The information you get from an AI doesnt change. The purpose of having a second is to take over from the first, when the first fails. The only extra useful information is the ability to check one against the other BUT you still need to be sure you know which one to believe so there is an additional inherent danger in having two of which you need be aware. |
Regarding the above, is it sufficient, according to the regs, to simply tape a piece of paper with the text "U/S" (or something to that effect) over an INOP instrument? Or do you really have to physically remove the instrument from the aircraft, or at the very least disconnect it from power/vacuum/pitot/static sources? (The latter requiring a trip behind the panel of course.)
I have, on a number of occasions, taken off with an U/S instrument that was not required for that type of flight (day VFR), and simply taped a piece of paper over said instrument - more to prevent confusion than anything else. Was I legal? (In an JAR member state, but I would be interested in the FAA position as well.) And as an aside, if you disconnect a pitot/static instrument from the pitot/static tubes, do these connectors auto-seal or do you have to put some kind of plug in them, to prevent false readings on other pitot/static instruments? |
replacing the traditional instrument with a second AI The instrument that most effectively indicates the attitude must be on the panel in the top centre position; [/font] in the position of the TC. if you disconnect a pitot/static instrument from the pitot/static tubes, do these connectors auto-seal or do you have to put some kind of plug in them, to prevent false readings on other pitot/static instruments? That said, an instrument which is legally not required, can be temporarily labled "inoperative" in place if secured properly. This is with the expectation that it will be removed by maintenance personel in the near future, either permanently, or for repair. The only reasonable exception I have seen to this is where a secondary instrument like an ammeter is in a cluster (can't be singularly removed) and it has been disconnected, and replaced with a new, separate ammeter. Then you'll sometime see a permanent "inoperative" on its face. The replies on this thread are not intended to confer maintenance authority to pilots. What you have here, is guidance telling you what, and where to look for the regulatory information you need to properly care for the aircraft you are flying. Know your privilages, responsibilities, and capabilities! Saying that you read it on PPRuNe is going to look pretty poor, when challenged by your local authority for unauthorized maintenace of an aircraft! |
Pilot DAR - you have lost me - the second AI is replacing the T and S not the primary AI.
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I understand that the proposal was to replace the t&B/TC with a second AI, in that position, but doing so would not conform to the design requirement stated. Though you still would have the original AI in its proper position, the design requirement does not provide for also providing that information in a non-conforming location on the instrument panel (and prodiving the expected T&B/TC information elsewhere).
In instrument flight, there is an expectation of an effective instrument scan, with the pilot finding information in the panel location expected. A second AI in a non conforming location has to potential to disrupt this. Not having the T&B/TC there certainly does, were "needle, ball and airspeed" flying become necessary. If a second AI is proposed, it should either be in the corresponding copilot's panel location, or top centered, as is common for glass cockpit aircraft. Instrument location in the panel is one of the times when standardization for flight safety is a very good thing. |
No, I dont think so.
Compare cockpit photos of a DA42, Cirrus and Mooney - each has a different location for the backup AI. The reversionary AI on the G1000 and R9 throws up yet another placement. |
I do accept that some aircraft might have a standby AI in a varied location, as the panel space and other considerations permit. Presuming that such placement is defined in the original approved configuration of the panel, there will have been an assessment of the design, and following that, an approval. If the designdid not follow the design standards, there will have been consideration of the affect, perhaps even an equivilent safety finding. That information is not generally available. Ideal? Perhaps not, but the best that was possible with the design. Sometimes things like how much depth behind the panel is available dictate where certain instruments end up.
If the AI was placed "somewhere" on the panel as a part of a retrofit, or modification, either it went through a similar evaluation and approval process, with a DER/DAR, or local equivilent, or perhaps it is just not approved! Glass cockpits are certainly causing a need to rethink panels in general. I'm sure that by the time I retire from flying, round instruments will be as uncommon as tailwheels are now! By the way, the first time I flew G1000 was in a Caravan. Neither of us had flown the G1000 before. I flew while the other pilot worked out how it worked. The only thing that neither of us could figure out was where the slip indicator was in the display. Only after some deliberate wild skids and slips to see what moved, did we work it out. A good idea ultimately, but a little too subtle! |
Only after some deliberate wild skids and slips to see what moved, did we work it out. A good idea ultimately, but a little too subtle! The position of a stand by instrument is a compromise. There will be a turn and slip somewhere on any IFR certified panel. The designers obviously believed the location of the turn and slip was adequate for partial panel. That is the first hurdle. The second hurdle is are you better with an AI in the same position as a the turn and slip, and if you are, why didnt the designer put one there? Well he didnt put one there because of cost. They either both need to be electric on different systems or electric and vac. Either way it is not an insignificant cost. Combine both AI with slip indicators or even just a slip indicator on the main AI and you have a fine solution. Alternatively put the slip indicator somewhere else because it is hardly essential if one or other AI is working. However if the turn and slip is certifiable where located I dont see what difference there is if you put an AI in the same hole instead of the T and S? It essentailly does the same job - just better. |
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