Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Habu on May 17, 2005, 06:02:36 PM
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Today I went flying and something very strange happened. I actually figured it out although the local AME was baffled.
After taking off the following gauges all started to fluctuate quite badly.
The Airspeed indicatior, the VSI, the altimeter, the manifold pressure and the tach.
The needles were swinging back and forth over an arc of 10 minutes on a watch face. The tach was really going crazy moving 30 mins in each swing.
The engine and prop were running smooth and all the engine gauges were fine.
What was wrong with the plane?
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Vaccuum leak?
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Electrical Problem?
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The ASI, VSI and altimeter are pitot static, so not electrical. Tach and manifold pressure could be connected, fluctuations in engine pressure can be connected to uneven running engine, but the rest of the gauges and sounds didn't indicate that, based on his description.
Hmm.... I'm thinking....
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A..... short in the pitot heater, resulting in intermittent activation?
meh....
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Not sure what was wrong with the plane but the pilot should have RTBed instead of flying around for 30mins with his gauges ****ed up.
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Doesnt your gages and stuff usualy go berserk right before your abducted by aliens?
In all seriousness though, I know a plane can be flown by feel and outside the cockpit, but I woulda wanted to turn back as well.
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I think he meant the tac was swinging in an arc equivalent to 30 minutes on a watch face, not that he was flying for 30 minutes with screwed up guages.....At least I hope that's what he meant.
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Was this by chance a post maintenance test flight?
Was the pitot static system worked on?
Was the aircraft just washed?
Hard to diagnose without at least a bit of history.
RTR
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Originally posted by Wolf14
In all seriousness though, I know a plane can be flown by feel and outside the cockpit,
Ask JFK Jr. for more details about this technique.
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As RTR pointed out, you didn't give enough information for someone to come up with a logical answer. Even basic things like current weather, what kind of tach (analog or digital), what kind of airplane.
Originally posted by Habu
all the engine gauges were fine.
Las time I checked, Tach and Manifold were "engine gauges."
Why would you be asking the opinion of an AME unless it was something related to medication you'd taken, which caused you to halucinate the whole thing?
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Maybe he means A&P?
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hehe Jigsaw, an AME is like an A&P in the states (only better )
A.M.E. Aircraft Maintenance Engineer.
I only used to be able to spell that, but now I are one.
RTR
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:lol Thanks for the info RTR. I'll admit the dummy card on that one. Only ever heard it referred to in the medical sense before.
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Well....we are kinda like doctors. Just fussier;)
RTR
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Typical Pirep, no wonder he was baffled.
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LOL Creamo.
"wingnut loose in cockpit"
"wingnut removed (unapproved part)"
(srry Habu, couldn't resist)
:rofl
To be fair, I hold a commercial Heli as well as an AME licence. But do all my dumb stuff flying, not fixing.
:p
RTR
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Originally posted by RTR
....Hard to diagnose without at least a bit of history...
too be fair, he called the thread Real life aviation test question. in my experience with FAA knowlegde test questions, this is a good & vague amount of info to be one.
I'm stumped, but on an FAA test i would still have a 1 in 3 chance of being correct
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Originally posted by Thrawn
Not sure what was wrong with the plane but the pilot should have RTBed instead of flying around for 30mins with his gauges ****ed up.
Sure what street should I have landed on in Downtown Toronto?
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Originally posted by jigsaw
As RTR pointed out, you didn't give enough information for someone to come up with a logical answer. Even basic things like current weather, what kind of tach (analog or digital), what kind of airplane.
Las time I checked, Tach and Manifold were "engine gauges."
Why would you be asking the opinion of an AME unless it was something related to medication you'd taken, which caused you to halucinate the whole thing?
I have a JPI engine analyzer which shows each cylinders temp and EGT plus the oil temp. All were normal. The fuel gauges were normal. The oil pressure and temp gauges on the dash were normal. In Canada we call them AME (Aircraft Maintanance Engineer). When the gauges went wacky I was just as much in the dark as to what was causing it as you.
I landed at the first oportunity and had a trusted AME check them out. On the ground everything was fine. I took him for a circuit and it was fine. After I landed and he got out I flew back to my home airport and the problem happened again. It was then I figured out how all these supposedly unrelated gauges were all being affected together.
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Originally posted by Habu
Sure what street should I have landed on in Downtown Toronto?
Island Airport.
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I should add some more information. The plane is a 1958 182 and most of the gauges affected were the original ones. The vacuum system was fine. The electrical system was also fine. The plane had no water in the static system and the pitot was not iced.
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I'm not a pilot, but I'd take a wild guess it has something to do with the area around your home airport? Some kind of rf interference?
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Originally posted by Thrawn
Island Airport.
Hey you think like I do. That is where I did land at first.
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I will post the answer tomorrow. He is a clue. The AME asked me if it happened right after take off. I said no it happened after I was at alt but still had the power on.
I asked him why he asked that. He said sometimes an unbalanced wheel can make all the gauges go wonky after you take off.
Eureka I though on the way back and it happened again.
And no it was not caused by an unbalanced wheel.
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flaps, turbulence? Something that cause the plane to vibrate?
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Originally posted by Habu
I have a JPI engine analyzer which shows each cylinders temp and EGT plus the oil temp. All were normal. The fuel gauges were normal. The oil pressure and temp gauges on the dash were normal. In Canada we call them AME (Aircraft Maintanance Engineer). When the gauges went wacky I was just as much in the dark as to what was causing it as you.
I landed at the first opertunity and had a trusted AME check them out. On the ground everything was fine. I took him for a circuit and it was fine. After I landed and he got out I flew back to my home airport and the problem happened again. It was then I figured out how all these supposedly unrelated gauges were all being affected together.
A couple questions here first.
What make / model plane were you flying?
Do you have the tach and manifold pressure displayed on digital or steam guages. Digital like the JPI.
Were you in icing conditions? I assume you were VFR or that the IFR guages were functional.
Are the VSI and altimiter digital?
I ask these questions as the typical small plane has seperate systems for engine and flight guages and only 2 would be related for input.
Example, the altimiter and manifold pressure both require a static port for ambient pressure otherwise they are not related systems wise.
The tach is typically a cable driven item and has no relationship guage wise to the others.
IF you have a complete digital engine display system with tach, manifold pressure, cyl temp., oil temp and pressure these could be affected by a bad ground and give erratic readings. That would not explain the altimeter and VSI. A static port partially obstructed would do that. Provided the altimeter is connected to a shared static port with the VSI. That presupposes you have a non pressurized aircraft.
You need to provide additional info. to make the diagnosis.
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Originally posted by Maverick
A couple questions here first.
What make / model plane were you flying?
Do you have the tach and manifold pressure displayed on digital or steam guages. Digital like the JPI.
Were you in icing conditions? I assume you were VFR or that the IFR guages were functional.
just read up, lol.
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He's a MAVERICK. He doesn't have to play by your RULES.
Negative, ghost rider. The pattern is full!
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Funky magneto.
Or it's probably the fluxor valve. I'm going to need 2 quarts of antifreeze, preferably Prestone...no make that Quaker State, some gauze pads and some 20 weight ball bearings.
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I missed that one post, EXCUUUSE ME! Now nuke go base jump off the eifel tower. :rolleyes:
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my guess is, since all these instruments but the RPM are related to air pressure, you were flying in an area where the pressure gradients were really high.
Most likely, caused by uneven heating of the surface.-an industrial area with lots of factories maybe?
I don't know why the RPM would change, can't think anything right now except that it was affected by the MAP changes.
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I'm pretty sure the doohicky was honkered by perfrazzle in the thingamajig.
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Originally posted by Maverick
I missed that one post, EXCUUUSE ME! Now nuke go base jump off the eifel tower. :rolleyes:
Just trying to help you.
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Originally posted by NUKE
Just trying to help you.
maybe it's time to add Maverick to your list there, Nuke. :)
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shreck, this is easy!!!
Flux Capacitor.
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Do you have alt vac.?
was it on or was a window open a bit?
vent in the cabin?
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I was thinking the same thing, but alternate static port wouldn't mess with the tach.
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loose spring/lever/switch which ever turns the arrow
or
magnetism on the dials was reversed by a cellphone etc.
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Originally posted by Habu
Hey you think like I do. That is where I did land at first.
My apologies, I made the assumption that the problem occured shortly after takeoff.
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Originally posted by Habu
I have a JPI engine analyzer...
I'm not at all familiar with that setup. Without knowing the system, schematics, etc., anything I come up with would be a WAG. It's possible to get all kinds of fun gremlins from things as obscure as certain manifold/rpm settings, but like I said not knowing the system, I can't offer educated input.
Down here AMEs are the medical examiners you go to for your flight physicals. I got to learn something today. :D
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Do these guages have lights in them?
I take it there was no vibration
what was the alt. doing?
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Bad tach Cable.
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What does bad tach cable have to do with vacuum components going back and forth?
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Fools. It's so simple, maybe you need a refresher course. It's all ball bearings nowadays. It's a plugged Fetzer valve.
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The next time you private pilots get in a plane, hang a necklace from the ceiling. If your instruments go out, just watch which way the necklace hangs.
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Originally posted by zmeg
Bad tach Cable.
Wow.
You are good.
That is exactly what caused it.
Explaination to follow in a bit.
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I have seen this once before..If you look around at all the avionics dials and switches,look closely at the one big knob in the cockpit that causes most of the problems.
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I will ignore the comments about blameing the pilot or not explaining the problem well enough. This is a real problem that really happened to me. How I handled it is how I was taught. Do not panic, try to see the extent of the trouble and look for the cause.
First thing you should do when a gauge starts to go crazy in your airplane is not abort the flight and land asap. It is to do a quick trouble shoot and try to see if the problem is real or just the gauge. A faulty gauge is not a reason to declare an emergency.
In my case the JPI readouts show me everything I need to know about the engine (except the fuel level) and those numbers were all fine. Second thing to do is use your ears. In my case even though the tach showed wildly fluctuating RPMs (I have a constant speed prop) my ears told me that the prop was not surging. Every time you fly and do a runup you surge your prop as part of the check. It is a very noticable sound.
So for those of you who said RTB or land asap I would have to say. Not necessary or even prudent in this case.
The problem was hard to find because so many things were being affected at the same time. The key was to identify what the main problem was and see how it could cause all those other problems.
Anyone who has studied ground school knows that all those gauges have nothing singularly in common. Some run on static pressure, some run on static and pitot, manifold pressure is static and the pressure of the mainfold and the engine tach has no connection to any of the others as it is a simple wire running off the engine. So to suspect the pitot or static or electrical systems was the cause was not logical.
When the AME told me an out of balance wheel can cause all the gauges to read like mine were I realized that the cause was vibration. But what was causing the vibration? It was the broken tach cable.
When this cable breaks it can still turn as the ends are touching in the sheath and when the bottom one turns, it can rotate the top one even though they are not connected anymore. It can vary from a normal reading with little induced vibration to a really wonky reading with lots of vibration in the cable. It can even go to zero if the cables really come apart and stop turning all toghter. That can make the tach reading very intermitant. And the cable can really vibrate when all this is happening. So that is why the tack was showing such a screwy reading.
The tach cable was vibrating the tach gauge and since the gauge was fixed to the panel it was vibrating the rest of the instruments so that is why all the other gauges started to fluctuate.
The plane is now waiting on a new tack cable. I hope to be back in the air next week.
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Well duh!
That's what I said.
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Originally posted by SunTracker
The next time you private pilots get in a plane, hang a necklace from the ceiling. If your instruments go out, just watch which way the necklace hangs.
And if it just lays flat against the ceiling.
Pray
:lol
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Originally posted by SunTracker
The next time you private pilots get in a plane, hang a necklace from the ceiling. If your instruments go out, just watch which way the necklace hangs.
and hope you're not in a coordinated turn which becomes a coordinated death spiral.
1G steady up and down, right until you hit the ground. This is what caused me to redesign an autopilot I built for a project that used ADXL20 accelerometers instead of spendy piezo gyros.
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HABU
I asked about vibration (for some reason I felt in your story you had none).
Neat story and test, I had a tach cable break (it was just a bit to short and had a tight bend where it went into the tach) but only the tach was effected on my Cessna. It did the same thing as yours worked fine when cold but as things heated up it must have pulled the ends apart and then went screwy. But NO other instruments were affected, I was really stumped and was even thinking about power surges in the instrument lighting but that seemed wrong.
I flew VFR for another two weeks and prob. 6 hours waiting on the new cable. My AP/IA friend loaned me a portable optical tach that you just set on the dash with a bit of Velcro and the CDS cell counts the prop blades and divides by two (selectable for up to 4 blades)
You really can get by without a tach by using the MP and an experienced ear.
Take care and may the sum of all your landings and takeoffs be divisible by 2.
Scott
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Good catch Habu. If it was a more advanced plane I'd be thinking inverter, but you mentioned that it wasn't an electrical problem. I've seen vibrations cause those sorts of problems, but a wonky tach cable is a new one on me. One thing that did strike me was that all those instruments were "direct reading" analog gauges, not anything that read from an electrical source, so the other thing that I'd have checked was just random damage behind the instrument panel, maybe something pinched when it was put back up after it's last inspection.
Learning your plane well enough to fly by the "seat of your pants" is a skill experienced pilots should learn. Learn rules of thumb, and during each flight recheck them to make sure they still apply. As a T-37 instructor, you could give me an altitude and airspeed and I could tell you within 1% what throttle setting you'd need, what fuel flow you'd burn, and how far you could go. In the opposite direction, I could tell you exactly what RPM I needed to set to fly in any situation within 5 knots, whether it was climb, cruise, an ILS, or an overhead pattern. I could tell you how many pounds of fuel per mile you'd burn with the gear up or down, at any altitude. I had rpm corrections for normal speeds, with rules of thumb to correct for nonstandard temperatures at any altitude.
Knowing your plane inside and out, and more importantly just noticing how everything ties together, can save your life. Here's a little example. The numbers might be a little off as this was 15 years ago, but the idea is the same. As a 17 yr old student pilot, how would I have landed my Cessna 152 if I'd lost my airspeed indicator? Well, I'd trim up the plane for level flight at 2100 rpm. In the turn to base, I'd reduce rpm to 1900, apply one full swing of the trim wheel, and let the plane start to settle. At the base to final turn, I'd reduce rpm to 1700, apply 10 deg of flaps, and 2 more swings of the trim wheel. I KNEW from experience (all 40 student hours of it) that those actions would let me fly at a safe airspeed into a 10 knot headwind on final, even if the plane had a totally busted pitot/static system and an inop stall warning horn. Add 100 rpm or so for each 5 additional knots of headwind. For a power-off landing, it was 3 and a half swings of the trim wheel, controls loosely held so I'm not pulling into a stall, and set 2/3 ground and 1/3 sky in the windscreen, which also works remarkably well in the T-37 around the final turn btw.
Don't use those numbers since they're from a faded memory, but the idea works. Every plane type has characteristics that simply don't change much, even between different tail numbers. Sure one plane may have a higher pitched cruise prop or one may have extended fuel tanks which makes it heavier, but the idea still works. Take the time to look away from the primary instruments and notice what everything else is doing in various phases of flight, and it may save your butt. Do you KNOW what it sounds like 5 knots above the stall? What about the noise level at maneuvering speed? As you approach the stall, do you feel anything different in the rudders? Do the ailerons seem to "sag" as you approach a stall? How many knots do you get for each full throw of the trim wheel in a cessna? What rpm change does it take to keep level flight at approach speed with each additional notch of flaps? How does that change when you've got some fatboy in the seat next to you?
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Great last couple of posts.
I did 2 landings yesterday with basically no instruments. The readings from airspeed were off by 20 knots and the rest of the panel was not reliable as well.
The wind was about 12 knots and at the Island was 50 degrees crosswind.
I landed almost like you said. Pulled the power back to each position based on memory of the engine sound. Trimmed the same way as you describe and used 3 notches of flaps during the flair.
I realized that I was probably within 5 mph of a normal approach based on the sink rate and length of the float over the runway. I would like to have used less flaps in the crosswind but I put them on to get the speed to bleed off quickly.
Made me realize the value of landing without looking at the instruments once in a while as practice.
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Habu,
I would unscrew the tach cable from the drive and pull out the cable you can get to and reattach the housing (to prevent oil leak).
The shaking of the instruments cant be good for them. If you are waiting on a cable and still want to fly I think that would be a good idea. Replace the housing and not just the cable (like you needed to be told that gem of wisdom :D )
I would hate to see that cable get bound up in there and tear through the side of the housing and start whipping around in the rear of motor, there are lots of fragile stuff back there.
my $.02
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Good advice. But the damage was already done. When they pitot tested the airspeed indicator they found it off by a large margin. So it is getting rebuilt. The tach was fried and could have been the reason the cable snapped. Hey it was only 47 years old. Maybe still under warrenty.
Anyway the plane is grounded now that the airspeed indicator is not in it. No flying for at least a week.
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Actually Habu, that bird should have really been grounded when it happened the first time. With manifold pressure and engine rpm not reading correctly, you are short 2 pretty important engine indicators.
Strictly speaking, IAW CARs and Standards they are required instruments and must be operational for flight.
If they ain't working, your CofA technically is not in force.
Not trying to stir the pot (I probably would have taken another "maintenance flight" home with it too), just saying.
It's always a good idea to CYA in this type of thing.
Cheers,
RTR
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GOOSE A CAT
Items needed, according to the FARs:
Gas gauge
Oil Pressure
Oil Temperature
Seatbelt
ELT
Altimeter
Compass
Airspeed indicator
Tachometer
Nothing about manifold pressure being legally required, but I guess it's a pretty strong suggestion if you're using a CS prop. :D
But of course, there's no hiding from YOU guys that I'm a low time pilot, so if there's an error in my assertion, lemme know. The above is what I've been taught and is consistent with what I've read in FAR/AIM, but IANAL, especially not an Aviation 'L'.