How to scare yourself to death

Now, I realize that as intrepid aviators we know not the meaning of fear (riiiight...) however, I had an interesting experience today. I had flown to a nice grass strip about 20 minutes away and executed my first off-pavement landing and takeoff in my 6A. After climbing away, I was still congratulating myself on not folding up my nosegear and polevaulting into the weeds when I noticed one of those things you NEVER want to see in your cockpit, namely a flashing red light on my EI engine monitor drawing my attention to the fact that the gauge was showing ZERO oil pressure. That tends to get you interested quickly. Quick scan showed normal oil temp, normal CHT's, and the engine running just as it always does - no change in sound, power, etc. Nevertheless I was just turning to return to the strip I had just vacated, when suddenly the pressure indication returned to normal. Observed this for a minute, and made a judgment call to return to my home base, about 15 minutes away at that point. Most of the way home the pressure stayed right where it should be, but occasionally would drop somewhat, and once or twice briefly went to zero again, then stabilized again. I called for a straight-in to get on the ground as quickly as possible, and then saw the pressure go to zero again when I pulled the throttle and lowered the nose on approach. Again, all other indications were normal, and the engine ran smoothly. Got on the ground in a gusty crosswind, rolled out and taxied to my hangar, with engine again showing pressure. Shut down and took a few breaths before climbing out. All indications were, however, that there was a bad sensor or connection in the oil pressure circuit, something I have had happen before with this system, so I was a bit wound up, but not too bad.

Now here is the part where I scared myself. I immediately trotted around to the oil filler door, popped it open and pulled the dipstick, and saw....nothing. It appeared to be bone dry, bereft of any oil whatsoever, which is the moment at which my recently puckered bum very nearly did a complete 180 and darn near cost me a nearly new pair of jeans. Strangely, though, there did not appear to be any evidence whatsoever on the belly of the plane of anything other than the normal seepage and blow-off that I am used to. Heart pounding, I collected myself and put the plane away, thinking of how close I had just come to an engine out emergency. After popping the upper cowling off, I again checked the dipstick, and, what's this? Looks like oil! With this revelation, I must have redipped that silly thing a dozen times just to verify that yes, it appeared to be showing 5 1/2 quarts of oil, and then the light went on; this oil only has 3 hours on it, and is still squeaky clean, and the first time I read it I was standing out in the bright sunlight. In other words, in those circumstances that Exxon Elite on the dipstick was invisible, thereby giving me quite a fright.

What a relief! Now I just have to identify the actual problem. Last time it was a loose crimped connection; hopefully that's what it is again this time, or a timed out sender, but I don't think at this point that I was minutes away from engine failure, and my jeans will live to see another day.

And you were worried about ruining a new pair of jeans?

..I learned about flying from.........

Gerry!

thanks for sharing. I too have had those moments where the hair on the back of the neck stands up...I've seen sudden variations in oil temp when I roll onto base. Really caught my eye, then the panic lessens....after all, I am GLIDING to a landing on a 9,000' runway!
....after a minute, I figured that my oil probe might have unported, showing the hot AIR temp instead? The needle returned to 'normal' as soon as I 'unbanked'...but oddly, I don't see this every time.

Here's a question; when you 're-dip' your clean dipstick, do you rethread all the way in? That's a difference of at least half a quart!?????

Ever seen the capillary 'urban legend', that semi-synth oils 'crawl up the dipstick' over time, making the first reading erroneous?

Was it 0 during your run-up? Or was it nominal and then went to 0 during flight?

I think you had a good outcome, but the decision-making might be less than optimal (not to criticize, just to raise the discussion point...a zero OP reading in flight would, I think, be cause for an immediate precautionary landing to investigate).

My $.02. I know the feeling, as I have been going through this with an unreliable fuel pressure sensor. A word of caution here that you have already learned. The symptoms you experienced can be similar to oil starvation in addition to a failed sensor. You can have cases where oil pressure comes and goes as you are sucking the precious few remains at the bottom of the case. Typically the intermittent pressure is lower than normal, but you can't always gaurantee that. My advice whenever seeing intermittent loss of oil pressure is to IMMEDIATELY confirm your oil quantity and troubleshoot.

Larry

No oil on the dip stick

Also glad to hear the outcome was better than it might have been. Your comment about not seeing any oil on the dip stick brought back a memory from my CAP flying days in Cessna 182s, which ran on a Continental 6 cylinder engine. I don't hear of this issue happening with Lycoming or other engines, but you never know.....

I was checking the oil during preflight for the first time in the morning, only to find nothing on the dip stick. I freaked out about the same way that you did, because this aircraft had made about a 3 hour flight over the Colorado rockies the day before. I wondered how this "no oil" reading on the stick could be possible. Without doing anything else I immediately went to the oil locker and got several quarts of oil to add to the airplane. After adding about 2 quarts I re-checked the dip stick again and it showed 12 quarts of oil - the maximum capacity for this aircraft.

So how do you go from seeing no oil on the stick at all to a full oil indiication on the stick after adding two quarts of oil? Turns out that this oil sump/dip stick combination would develop a vaccuum when left to sit for extended periods of time. If you re-dipped the stick again it would break the vacuum and the oil would move into the dip tube.

It only seemed to be a problem with this one aircraft. Regardless, this event caused me to change the way I check for oil by redipping the stick at least 2 or 3 times just to make sure, especially if it is the first flight of the day. Just thought I would share this because I too have been bitten by the "can't see the new oil on the dip stick" problem, but this is one other scenario that might also occur while checking your oil during your preflight. YMMV.

flyboy1963 said:

Here's a question; when you 're-dip' your clean dipstick, do you rethread all the way in? That's a difference of at least half a quart!?????

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Yes, I rethread all the way in

RV7A Flyer said:

Was it 0 during your run-up? Or was it nominal and then went to 0 during flight?

I think you had a good outcome, but the decision-making might be less than optimal (not to criticize, just to raise the discussion point...a zero OP reading in flight would, I think, be cause for an immediate precautionary landing to investigate).

Click to expand...

All normal during runup and the flight up to the grass strip. After landing there, I just reversed on the runway, backtracked, and immediately took off again. Climbed up 1000 ft and headed back towards home base, then saw the warning light a few minutes later, with the zero psi reading. At that point the grass strip was about 5 minutes behind me, and my home base about 15 minutes in front. I was actually starting my turn back to the grass strip when the reading normalized, so I levelled off and observed for 30 seconds, and rechecked all the other engine readings, as well as using my Mark I ear to listen for any changes in how the engine was running. Everything else seemed completely normal, so I made the call that the reading was MOST LIKELY erroneous, and kept heading for home, where I would be better able to troubleshoot, plus there's a longer, paved runway to land on, with the benefit of complete familiarity. I would be lying to you if I told you I wasn't second guessing that decision all the way home, though. If the reading had stayed at zero, no question I would have made the precautionary landing no matter what the other readings, etc. were, but the quick return to normal numbers and the erratic, inconsistent readings thereafter seemed much more in line with a fault in the sensor/gauge system than an actual emergency.

I appreciate the comment; I think it is a valid observation. When I read stories like this on VAF it always makes me think about the best response when faced with similar circumstances. Probably this story will prompt the same thinking on the part of others. I know I am still undecided as to whether the call I made was the right one in that moment or not, but the decision was made with the information I had in front of me at the time (return to normal readings), and once made I stuck with it.

Thanks again for the comment; productive discussion, and believe me, I take no offense!

Several times on this forum I have urged people to put in a mechanical oil pressure gauge as a backup to the electric one. It is for precisely these types of events that they make sense. No other engine instrument really needs a backup, but oil pressure does. When that electronic gauge tells me my oil pressure has dropped to zero, I'll know whether it is lying or not. The transducers we commonly use for fuel and oil pressure are notably unreliable.

If not a backup gauge, minimally one can use a low pressure switch on an idiot light. These, though, usually trip at a low pressure as compared to normal operating pressures.

AlexPeterson said:

Several times on this forum I have urged people to put in a mechanical oil pressure gauge as a backup to the electric one. It is for precisely these types of events that they make sense. No other engine instrument really needs a backup, but oil pressure does. When that electronic gauge tells me my oil pressure has dropped to zero, I'll know whether it is lying or not. The transducers we commonly use for fuel and oil pressure are notably unreliable.

If not a backup gauge, minimally one can use a low pressure switch on an idiot light. These, though, usually trip at a low pressure as compared to normal operating pressures.

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This sounds like an excellent idea. Forgive my ignorance, but is a mechanical gauge plumbed directly into the oil system with no electrical component at all? If so, that would seem to be a very worthwhile addition to the panel.

gerrychuck said:

This sounds like an excellent idea. Forgive my ignorance, but is a mechanical gauge plumbed directly into the oil system with no electrical component at all? If so, that would seem to be a very worthwhile addition to the panel.

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Yes, mechanical only. There needs to be a restrictor somewhere in the line near the engine (same as for transducers) so that a line break or gauge failure won't quickly dump oil. A manifold on the firewall works well both to mount the transducer and the 1/8" tube leading to the mechanical gauge.

so....I'm poking around under the cowl trying to sort this out, and I'm wanting to be sure I'm identifying the correct parts. I have two units coming off a firewall mounted block (first picture), both apparently fed by an oil line coming off the block just above the right mag (second picture). One projects vertically from the block and the other projects forward and looks more like a diaphragm. Both units have wiring coming off of them which joins into a large bundle which goes through the firewall. My gauge is an Electronics International digital combo oil pressure/oil temperature unit. Any and all help in identifying these pieces appreciated.

[/url]IMG_20151025_115439 by gerrychuck, on Flickr[/IMG]

[/url]IMG_20151025_115627 by gerrychuck, on Flickr[/IMG]

The longer one that sticks out vertical is the oil pressure sender.

The one that sticks out forward toward the prop (diaphragm as you called it) is a simple pressure switch. Likely used to power either a hobbs meter or low oil pressure light on your panel. You can see one wire connected to the terminal marked "NO" meaning normally open. The other wire is probably connected to a terminal marked "C" for common (either ground or +12v depending on how the builder wired it). It connects the circuit when the oil pressure is above a certain pressure (usually pretty low, less than 10psi or so).

You are a prince, sir. Thanks so much for the quick reply!

A question for the engine experts: if one sprung a leak and the oil was pissing out, what would the temps read? i would guess that if the leak was gradual there would be a gradual increase in oil temp, since you have less mass of oil to carry away the heat, but once you got close to zero there would be no oil getting to the sensor so the temp might drop? In any case, it wouldn't just go on reading perfectly normal would it? What would you expect to see when cross checking the oil temp in a real oil emergency? This would be useful for trouble shooting a faulty sensor in flight.

sblack said:

A question for the engine experts: if one sprung a leak and the oil was pissing out, what would the temps read? i would guess that if the leak was gradual there would be a gradual increase in oil temp, since you have less mass of oil to carry away the heat, but once you got close to zero there would be no oil getting to the sensor so the temp might drop? In any case, it wouldn't just go on reading perfectly normal would it? What would you expect to see when cross checking the oil temp in a real oil emergency? This would be useful for trouble shooting a faulty sensor in flight.

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In the reading (googling, lets be honest) that I've done over the past week, I found a fairly definitive expert answer to this question, and it wasn't what I expected. I found a bulletin from an aircraft engine maintenance company saying that it is completely possible to have all engine parameters except pressure reading completely normal until moments before the bearings seize, and they made that point specifically to warn pilots that normal temp and cht readings do NOT mean that your low oil pressure reading is erroneous. Their position was unequivocal; a critically low oil pressure reading means "get the plane on the ground NOW" no matter what your other gauges are telling you. It would seem that AlexPeterson's solution of having a backup mechanical gauge is probably the best, if not the only way to know in-flight whether you are looking at an erroneous reading or a genuine emergency.

I have a redundant system to help identify a total loss of oil pressure on my Midget Mustang.

As with the setup pictured on this page (above) I have a pressure transducer for an oil pressure gauge as well as a pressure switch for my Hobbs meter.

My pressure switch has BOTH a normally-open (N.O.) contact AND a normally-closed (N.O.) contact. I use the N.O. contact to activate the Hobbs meter when oil pressure is applied. The N.C. contact is used to extinguish an idiot light on my panel when oil pressure is applied. An added benefit is that there's a big red light on the panel when I leave the master switch on when the engine isn't running. I don't know if ALL Hobbs switches have both contacts, but it'd be a very easy and inexpensive retrofit if you've already got a single contact switch installed.

As added redundancy, I have two separate pressure sources coming off the engine. One is exclusively for the gauge's pressure transducer, and the second pickup drives the Hobbs meter and idiot light pressure switch. Granted, I now have 2 lines instead of one coming off the engine and either one of them could be a potential failure point causing at least a little oil loss, but I *do* like the redundancy to confirm or dismiss a complete loss of oil pressure.

Does it work? Yes! Due to what ended up being a persistent case of cranial-rectal inversion, I have had occasion to prove the warning system in flight on not one, but two different flights! The first time, I saw the pressure gauge before the light and the second time, I smelled the smoke and saw the light at about the same time.

RWoodard said:

I have a redundant system to help identify a total loss of oil pressure on my Midget Mustang.

As with the setup pictured on this page (above) I have a pressure transducer for an oil pressure gauge as well as a pressure switch for my Hobbs meter.

My pressure switch has BOTH a normally-open (N.O.) contact AND a normally-closed (N.O.) contact. I use the N.O. contact to activate the Hobbs meter when oil pressure is applied. The N.C. contact is used to extinguish an idiot light on my panel when oil pressure is applied. An added benefit is that there's a big red light on the panel when I leave the master switch on when the engine isn't running. I don't know if ALL Hobbs switches have both contacts, but it'd be a very easy and inexpensive retrofit if you've already got a single contact switch installed.

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That looks like an excellent idea.

gerrychuck said:

It would seem that AlexPeterson's solution of having a backup mechanical gauge is probably the best, if not the only way to know in-flight whether you are looking at an erroneous reading or a genuine emergency.

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Unless you have a constant speed prop.....

In that case, an actual loss of oil pressure will cause a loss of RPM control, which will be a cross check indicator that it is a real problem.

I think the best system I've seen is a low oil px light run by a separate transducer in addition to an oil pressure gauge. If the gauge indicates low pressure without a corresponding low oil pressure light, that likely indicates a sensor problem.

So, I had my local shop check the plane over by hooking up a mechanical oil pressure gauge and comparing to the electronic gauge readings. In their testing, they were unable to replicate the fault. Wiring all seems intact, and the transducer apparently functioned perfectly during the test run, so the cause of the glitch remains unknown. Their suggestion was to replace the transducer if it happens again. Seems like a reasonable approach.

I am thinking very seriously about changing my Hobbs switch to allow wiring a warning light. This seems like a very simple and useful change that makes a lot of sense.

Or....I could always go with rvbuilder2002's constant speed prop solution. Sure, it would cost me an extra $10,000 or so, but what price can you put on safety? (I'm practicing that line here before trying it on my wife...)

Flew the plane for the first time since experiencing the zero oil pressure anomaly and having the shop check it out (and find nothing). Ran like a top and the oil pressure readings were steady at 74-75 psi in cruise. So...still no idea why I experienced those readings on the last flight.

Two things were different from "the usual" on that flight. First, I landed for the first time at a grass strip with what felt and sounded like very dry grass, and had just departed that strip a few minutes before experiencing the anomalous readings. Second, I was a bit inattentive with the butterfly valve that controls cooling airflow to my oil cooler, and let my oil temps get a big higher than usual (as I recall it got to about 205 degrees). The other time I had faulty low OP readings I also had high oil temps; I had covered the intake to the oil cooler with foil tape for the winter, and was flying on an unseasonably warm day. This was what led to me installing the butterfly valve, even though the faulty readings were attributed to a loose crimped connector. Makes me wonder if there could be any connection. Today I kept my oil temps at about 185 and readings were solid as a rock. Interesting.