Weird winds or something more serious?

Editor’s Note: This is the latest article in our series called “I Can’t Believe I Did That,” where pilots ‘fess up about mistakes they’ve made but lived to tell about. If you have a story to tell, email us at: editor@airfactsjournal.com

I had my Private License for a few years now and was working in the FBO where I had done my training. I had a good relationship with the instructors, and frequently took flights and simulator sessions with them to stay involved and current. I was not instrument rated, but would take any opportunity that came up to go flying, either VFR or IFR.

Mike, one of our instructors, and I made a plan to fly the club Archer II from Farmingdale, NY (KFRG), our home base, to Bradley International (KBDL) in Connecticut. It was a mild evening in January.  A high overcast around 3000 feet, temperatures were in the mid 40s, freezing levels were high, and good visibility beneath the clouds–a perfect night for a basic IFR training flight.

Vacuum gauge
If you expect it to be in the green, will you notice when it’s not?

The preflight was uneventful, and before long, we were ready to takeoff on runway 1. Lining up on the runway, I checked the compass to the DG and found it not in agreement. A quick adjustment to the DG, and a mental note to be more attentive, and we were on our way. The climb out was uneventful. Smooth air and great visibility made for a nice start. The approaching ceiling filled me with excitement and I prepared myself for flying on instruments.  Mike had worked with me on prior occasions in the sim, but this time it was for real.

We entered the clouds and I transitioned to instrument flying. After a few minutes, I settled into a basic instrument scan and we flew along in the smooth, continuous overcast. Mike explained how to set up the radios and navigation aids for the upcoming ILS and we reviewed the charts. As we reviewed the charts, I noticed that I was drifting right of course and had to continually make left corrections to keep on the radial. As we continued on, and the corrections continued, we remarked that perhaps there was a significant crosswind. Seemed odd that there was no turbulence, and the strong winds were not forecast, but that was all that came to mind and on we flew.

We received radar vectors to intercept the final approach to runway 6, and established ourselves inbound. The correction continued, and we were surprised at the correction we had to hold to track the localizer. Before our curiosity could get us to explore other options, we broke out of the clouds, and flew the last three miles visually to the runway. The landing and taxi in were uneventful, and the weird winds quickly left our minds, or at least mine.

We departed about 45 minutes later, and within 10 minutes were on top of the undercast, enjoying a smooth moonlit evening flight home. It was difficult focusing on instrument flight when I could see perfectly, but soon it became evident that the clouds must not be uniform, as I was constantly entering a left turn. I gave myself a second scolding and reminded myself to focus on the gauges. As I did so, I immediately found myself disoriented. The clouds made it appear as if I was turning, yet the attitude indicator was straight and level, but wait…the turn and bank indicator was showing a left turn too. The compass was turning as well, but in the other direction. I immediately looked over to the vacuum gauge, and couldn’t see the needle, it was pegged on zero. Looking back to the instruments, I saw the VAC light shining brightly–a complete vacuum failure! I immediately called out to Mike, who had been reviewing the return charts, that we had lost the gyros, and that they were spinning down.

Between the fear and adrenaline, I found the time to be amazed and fascinated by the slow and smooth tumbling of the attitude indicator. I had always though that when they failed, their tumble would be obvious. I trembled at the thought that, had I been in the clouds, how far would I have banked before I figured it out. It was a very slow turn, Mike hadn’t even noticed.

While I was now established back in straight and level, one glance at the instruments gave me an immediate sense of the leans. Two pieces of index cards covered the errant instruments, and for the remainder of the flight I recited “Needle, Ball, Airspeed” in my head, to remind me what to look at and interpret, and to keep my anxiety level at a mild panic. We were still VFR on top (conditions, not the clearance), and we decided that I would continue to fly the aircraft (aviate) while Mike would navigate and communicate. Mike notified ATC of our predicament and together they planned for the descent to come. We decided to descend over land instead of Long Island Sound, and ATC vectored us over the Long Island, turned us west, and cleared us to descent to VFR, or 1000 feet, whichever came first. The descent was uneventful, “needle, ball, airspeed” the entire way down, and we finally broke out at 1800 feet and flew visually back to Farmingdale a few miles ahead.

The Six Pack instruments
Which one can you trust?

Looking back on this flight, a number of flags go up in retrospect, and while I could make excuses, I choose to blame my complacency as one of the root causes. For years, I have always checked the vacuum gauge during preflight, and it has always been at 5.0. I know I looked that night, but was it at 5.0 or did I expect to see it at 5.0 and assumed that was where it was? Same goes for the DG. I didn’t forget to set it after start, and a flag should have gone off when we lined up on the runway 10 minutes later and it was off.  Crosswinds?  Visual illusions? I had reasons for everything, except the most obvious. I also had an instructor on board.

After this experience I quickly ordered some instrument covers so if it were to happen again, I could completely cover the errant instrument. Even with the index cards covering most of the gauge, I could still make out the indications around the edges, giving me a mild sense of the leans until I refocused.

I also recommend that anyone who flies watch their attitude indicator spin down when they shut down. It will give them an idea of just how slowly it actually occurs. Let ATC know immediately when you have a problem. They were instrumental in helping devise a plan, and the calm voice over the radio helped keep the atmosphere in the plane calm.

Lastly, complacency can kill. Listen to the warning signs, flags, dominos, or whatever you may call them. The DG being off on lineup at KFRG should have made me stop the takeoff run and re-check everything. The “winds” and “visual illusions” were just more confirmations that things were not well, and each indication was at a progressively worse point in the flight. Having another pilot aboard didn’t mitigate the risk either. We both flew with each other frequently and we both perhaps were too complacent with each other, assuming the other would catch anything that was amiss. Defining roles here would have been a good idea as well, instructor or not.

Like I said, complacency kills. I had read plenty of articles just like this one before that flight happened. Each time I would be saying “Hey buddy, check your vacuum gauge.” It always seems so obvious until you’re actually there, in the situation. Luckily, in my case, we got home safe, and after the disappointment passed, I learned just a little more to make me a better pilot–at least better enough to write about it and hope someone else learns from this article rather than during the actual experience.

18 Comments

  • Jim,
    Good story, but it isn’t quite clear to me if you believe the vacuum had failed before leaving KFRG or sometime on the return trip. In the end, do you know if it was determined that the pump had failed or some other failure?

    • The next day, the mechanic brought the pump and tubing in. The vacuum pump had failed. My only thought, looking back, was it was failing at the beginning of the flight, but had not completely done so (slow leak? Low vac but still some pressure?). It was a night flight, and the vac gauge is on the far right, not the easiest to see. The winds were almost calm at the surface, and we’re supposed to be enroute as well, yet at one point we had almost a 20 degree wind correction to stay on the airway..again, I feel foolish that I didn’t look further into it back then (over 15 years ago)

      • Well actually, the annunciator light should have warned you in advance of the suction dropping below the point where the gyros didn’t work properly. That’s why I was wondering what the failure mode was. I could see, for example, if the tube to the DG was kinked it would cause the DG to spin slowly, but the AI would work properly and the vacuum gage would read normally or maybe too high if the regulator couldn’t keep up. If suction was on the high side, the extra load on the pump could cause the total failure which you experienced on the way back.

        I’m kind of a student of failure modes and this one is interesting. Would have to dig into the maintenance history though to figure it out I guess.

        • That scenario makes a lot of sense. The annunciators didn’t go on until trip back, that I know (they are right in front of your face, so those I would have noticed). The AI seemed ok on way out to Hartford, as I would have noticed it rolling when we went visual.
          I don’t recall what the mechanic said (it was almost 15 years ago) but I do recall him bringing out the pump and tubing to show us, so you may be right on. If I looked over to the suction gauge, and saw the needle, I may have assumed it was fine, when in fact it was running high. After years, perhaps as long as I saw a needle, I assumed it was fine with just a quick glance.
          Needless to say, I don’t “glance” anymore.

          • Yes, over the years I have also learned to notice slight differences in needle position as an indication of something changing. It is more difficult to pick up on small changes with a rental airplane however, since you don’t have a historical reference to go by.

  • curious as to why this was not picked up on your runups and checks prior your return flight . If in retrospect there was a vacuum issue during initial flight did you in fact have full vac on checks….?

    This being a question and not critisism and thanks for sharing with us

    • This is where I get into complacency. For years, that vacuum gauge always pointed right at 5.0, never wavered. After a while, I feel the check became cursory, and while I looked, my expectation was that it would be at 5.0, and in the dim lights, perhaps my expectations overrode reality. During the run-up, the only checklist item for the vacuum was to check the gauge. The annunciation lights were all out, I know I looked at the gauge, but after years of it always reading normal, perhaps I didn’t really look. The attitude and dg we’re drifting slowly on the way up, and didn’t fully fail until our return, hence my assumption that the vacuum was on its way out on the way up to BDL, and officially packed it in on the way back.

    • Yep, a license to learn. This one taught me to “pay attention” even when things are routine. Complacency kills. That’s one good thing about flying, there’s always something to be learned. When I stop learning, I stop flying.

  • Interesting situation and story. I used to take my vac gage readings during run-up more or less for granted, just looking for the needle to jump up but not really looking at the actual value … that is, until one day I had what I thought was a failing AI and a DG that seemed to drift more than it should. I reported it to my mechanic and he checked out the vac gage on a runup, and declared that it needed to be adjusted from the 4.6 it was at to 5.0 in. as specified … then thereafter the gyro’s ran just fine. I didn’t even realize until then that the vac pump could be adjusted!

    Anyway, a couple more thoughts on the topic of failing vac systems:

    1) The failure rate of vac pumps is pretty high compared to most other mechanical and electrical systems on piston airplanes … plan on it failing sooner or later in between overhauls! Always check and recheck the vac gage, not just at runup but also periodically in flight.

    2) I was happy to retrofit my Cherokee 180 with an S-Tec autopilot (now Chelton), because it runs off the electric turn coordinator. The TC has a much lower failure rate than the vac driven AIs on which most older autopilots depend (such as the original equipment Century IIb on my Cherokee). Of course electrical failures do occur, but again much less often than vac failures.

    3) It’s great that electronic backup AHRS systems are now available, and rather inexpensively, for operation with portable pad computer EFB systems … including the new Garmin GDL 39 which combines the AHRS with ADS-B-in, plus a backup battery in case of electrical system failure. There are other portable AHRS units available without the ADS-B-in. Every IFR pilot ought to have such tool in the cockpit! Redundancy is our friend!

  • Jim

    I think you did pretty well.

    1. You recognized a problem holding your course, but you held your course.
    2. You didn’t see the vacuum failure on the ground but it might not have fully failed, and you did recognize the failure in the air.
    3. You did correctly identified the failure and took correct action to maintain control of the aircraft.
    4. You used additional cockpit resources to ease your burden and contacted ATC for assistance.

    I am happy to share the air with you. You are a good pilot.

    • Thanks, Wayne. I’m my own worst critic, but your words are kind and appreciated. Well said, brought a smile to my face.
      Jim

  • I took a friend up, he’s a very experienced pilot but usually flies complex aircraft. I have a older 172.
    As we taxied out and did my run up he pointed to the vacuum gauge that it obviously was not working.
    Ah, but I don’t have a vacuum pump, I have a venturi! I had to explain it. We took off and as soon as the speed came up, everything was normal.
    Good story though.

  • Thanks for sharing your story. Good Crew Resource Management, once you recognized the failure. I believe the most important take away here is instrument scan. You will fly better and crosscheck equipment at the same time.

  • I have learned to check the suction not only during the power runup, but also during lower power settings and at idle. The suction will read low if the pump is getting weak. This leads to precession as you taxi on to the runway. (Of course, this can be caught by checking the heading against the runway as well.)

    • Hi Vicky, I just wanted to clearify something because it can be very important in the way pilots think about vacuum pump failures. Vacuum pumps rarely if ever fail slowly. When they fail, the output goes from normal to 0psi in a heart beat. The reason for this is there are carbon blades in side the pump that spin around. They normally rub against the case of the pump and because of the shape of the case, creates a vacuum side and pressure side of the vanes. Any dirt that enters the pump may wedge itself between the blade and the case causing the blade to break either a small peice or even the whole blade. Both cause a domino affect causing all the blades to break within a revolution of the pump.

      I bring this up because saying a vacuum pump is getting weak implies that the vacuum pump gives a warning to its own demise. This is not true. This is the reason that vacuum pumps are supposed to be changed with a new or overhauled pump every 500 flight hours. If there is a loss of vacuum at idle, it would most likely indicate a vacuum leak or a faulty vacuum regulator. A standby pump (either carburetor or electrically driven) is the best insurance against the loss of vacuum if you fly IFR regularly.

      Regards,

      Paul

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