Airspeed Indicator Failure

Discussion in 'Lessons Learned' started by Ted DuPuis, Jun 16, 2016.

  1. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    I posted this on the Twin Cessna forum, but I thought this would be a good lesson for pilots here.

    On the ferry flight when I flew the 414 from BVO to BIE for the annual, I discovered on short final that my airspeed indicator had failed. It did NOT fail by going to zero. It was sticking and thus not decreasing the indicated value as it should have, providing misleading information telling me that I was flying faster than I actually was. For an electronic flight deck, this would be given a hazard level of "Catastrophic." During takeoff and in flight I didn't notice anything that would have me believe the plane was flying abnormally or giving me abnormal airspeed indications, of course I was well within the green arc at that point, taking off faster from a long runway, etc. I also had never flown a 414 before, although I have about 1,000 hours in the 310 and another few hundred hours in Navajos and cabin class turbines.

    Because this was a new to me plane (both of type and specific aircraft), I made a 747 sized pattern. I also did this on last weekend's dog run, getting to know the plane more and keeping things conservative. Shallow bank angles.

    On about 1 mile final, I had 15 degrees of flaps in, indicating around 100 KIAS. The plane just "felt" slow and mushy. I had a long runway (over 5k feet), no need to do a short field landing, so I pushed the nose down, left the flaps alone, added some power, and came in to land. When I parked and shut off the engines, the airspeed indicator still showed 90 KIAS.

    I have no idea how slow I actually was. The stall warning horn didn't go off, but I'm assuming that I was down closer in the 75-80 KIAS range given how the plane felt on final (which is the bottom of the white arc). I Because I recognized the first indication of a stall (starting to feel mushy) I was able to do an easy recovery. Nose down, add some power. DON'T TOUCH THE FLAPS. I gained that extra few knots to make things more comfortable, did a partial flap landing (which is and should be a non-event). It was even a soft landing.

    The plane had been sitting for a long time. The right airspeed indicator was labeled inop, but the left one was not. I'm guessing that it was sticking because it had sat for so long.

    That said, we should always be vigilant about these sorts of things. Trust thine instruments, but cross check and verify. If you have a GPS, you could diagnose the above problem by cross checking airspeed and ground speed. Keep your stick and rudder skills up to speed and keep the rust off of them. Last week a Cirrus crashed for what appears to have been the same reason. The pilot was on her 3rd attempt to land the plane, and ended up in what was clearly a stall/spin from the video posted of the crash.

    Close to 2 years ago, a 414 crashed that had been sitting when the new owner was flying it (only weeks after purchase):

    http://www.ntsb.gov/_layouts/ntsb.a...-7b78-4716-b28a-518cbd095163&pgno=1&pgsize=50

    While the NTSB final report hasn't come out yet, the fact that it occurred while maneuvering at the destination airport and was a 3-turn spin would tend to indicate a stick and rudder issue, potentially compounded by a mechanical issue such as what happened to me.

    But, fortunately, I'm the one telling you about it, and not the NTSB.
     
  2. Cooter

    Cooter Pattern Altitude

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    Another reason to have an AOA indicator, it makes a good crosscheck.
     
  3. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Agree 100%. I had an AOA (Alpha Systems) in the 310 and this was one of the reasons I installed it.

    When the 414 gets its avionics upgrade I will probably get an AOA added as well.
     
  4. Let'sgoflying!

    Let'sgoflying! Touchdown! Greaser! PoA Supporter

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    glad to have you around still Ted.
     
  5. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Here's the airspeed indicator, now on my desk:
     

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  6. steingar

    steingar Touchdown! Greaser!

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    In my old airplane I almost never looked at the airspeed indicator. In the new one I'm still feeling around it but look less and less. Got better things to look at on landing. I'll probably always lookat it on takeoff to make certain I don't go too fast.
     
  7. Norman

    Norman En-Route

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    That sure rules out plugged pitot/static lines, which would have been my first guess.
     
  8. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    That was our first guess, too. My mechanic pulled both the airspeed indicators and we found very quickly that this one was broken.

    The nice part is I now have two freshly overhauled airspeed indicators that work perfectly. :)
     
  9. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    Wow! That's scary. I've never seen an ASI stuck like that.
     
  10. Matthew

    Matthew Touchdown! Greaser!

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  11. Zeldman

    Zeldman Final Approach

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    I have had 2 A/S failures in my career. One in a 172. It worked normally until the plane slowed to under 55 knots, then it just fell to zero. Another was in a C-207. I taxied out, took off and was at cruise when I noticed the A/S was still on zero. Since it was winter in Alaska, I turned on the pitot heat and that solved that.

    I have about 2000 hours in the C-414. Fun plane. Loved that I could get to the flight levels, although slower than a turbine, and still come in over the fence at 80 KIAS. Great in crosswinds, great IFR platform, even had one engine fail during climb. A no brainer to return to the airport. But like most pilots, I would have liked at least 25 more HP per side....;)
     
  12. ircphoenix

    ircphoenix Pattern Altitude

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    Wow. Your desk is pretty fast.
     
  13. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Yeah, it is scary. Still scares me a bit to think about, although didn't scare me at all at the time. I was too busy flying and I have a strict policy while flying: don't panic and fly the plane. :)

    I've had airspeed indicators read 0 before for several reasons. Ice buildup, mud daubers, etc. The misleading aspect of this one was more insidious and I think more dangerous.

    RAM solved the 25 more HP per side with the RAM VI conversion. Of course, that's some $$$. :)

    So far I've got about 20 hours in this plane and really liking it. Another 20+ planned over the next two weekends. I haven't taken it above 17k yet, but it's very happy in the teens and I like the low cabin altitude there. The baffles are also in rotten shape so I don't want to go too high with it, and it doesn't have AA intercoolers so I wouldn't expect great performance up there anyway. The low cabin altitude in the mid teens is nice, helps a great deal with fatigue. Especially so since this is a 4.2 PSID cabin, unlike the 421B/C or 414A with the 5.0 PSID cabin.
     
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  14. Jimmy cooper

    Jimmy cooper En-Route

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    In the Mooneys I flew, I checked the airspeed as I entered downwind and put the gear and flaps down then just watched my position and traffic as I was landing in 2200 feet.
     
  15. steingar

    steingar Touchdown! Greaser!

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    Right now I put the gear and flaps in before I hit downwind. Gives me a bit of breathing room close to the airport, where it is more likely there will be other airplanes to look out for. I still check it more than I like, but I'm still pretty new to it. Hopefully I'll get better at energy management and feeling the aircraft, and won't need the crutch of an airspeed indicator as often.
     
  16. Chip Sylverne

    Chip Sylverne En-Route

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    Fear is the poison of our lives.
    Had one fail on me in solid IMC on me a few years ago by oscillating up and down. Drives home the point, fly attitude, and know thy performance numbers. 18" and 2400 rpm gives me 120 kts with wings on the dot. 13" gear up gives me 500 rpm descent @120kts. Gear down 18" at same gives me 500fpm descent @120kts. I can fly an approach safely at 120kts and still get it slowed to land at minimums for Cat B.

    Know thy numbers.
     
  17. Cooter

    Cooter Pattern Altitude

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    Crutch has a bit of a negative connotation, I certainly don't think of it that way. It is a required piece of equipment so it shouldn't be regarded a weakness to use it.
     
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  18. Ted DuPuis

    Ted DuPuis Administrator Management Council Member

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    Exactly my thoughts. It's not a crutch, but like any piece of equipment, you need to know how to diagnose and handle its failure.
     
  19. RotorDude

    RotorDude Pattern Altitude

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    A skill that transfers well from gliding is judging airspeed purely by sound. On the second part of my glider checkride we took off and flew the entire flight (which ended abruptly with a simulated rope break at 700' AGL) with the airspeed and altimeter gauges covered. After couple of minutes, you start realizing that most of our precious flight instruments are just overkill, at least in VMC.
     
  20. Jimmy cooper

    Jimmy cooper En-Route

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    I should add here that when I first flew anything, mooney , Stearman, cessna 195, bonanza , etc. I always checked the airspeed indicator often until I got used to the airplane. Well over fifty hours each . The mooney turned out to be one of the easiest to judge and fly but only after I was taught by a mooney pro. He was amazing and I never came close to his talent. Don't want to imply I was " born to fly" as I was not. For some reason landings facinated me and I really like to slip to the runway especially in the Stearman. From 2000 feet , in a hard slip they drop like a stone. I regret I did not fly gliders. I'm sure they would have improved my skills.
     
    Last edited: Jun 16, 2016
  21. Rock

    Rock Pre-Flight

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    I had bought my own plane to use for training, the Cherokee 160 pictured. The CFI was just starting his school and didn't have his planes yet and was willing to train me in my own plane.

    My transponder was out of certification so I had a local accredited technician check it. He checked it out and said everything was fine with all the official looking stuff in my log books. Good to go right? I had no problems prior with anything. I was about 9 hrs into my training that day and was doing my lap or two around the airport with my CFI preparing me for my 1st solo.

    Runup was fine, vacuum pressure was spot on. I started down the runway and all instruments looked right. I glanced over to the oil pressure, fuel pressure and everything was a OK. I had the altimeter set and my ground speed was picking up as usual.

    I climb out at 80 knots and everything was going fine for the first 20-30 ft off the ground. Then I started loosing air speed with my runway getting shorter and shorter. I still had engine power and everything sounded right so I knew it was instrument related. I told my CFI, we have a problem. My air speed indicator isn't working properly. Then I noticed the altimeter wasn't working either. He simply said, you better climb out. I just climbed out with a less than normal angle of attack and got it up to what looked like pattern altitude. I kept a faster than normal approach and settled her down rather easily considering my state of experience. I was always proud that my CFI let me handle it. He never took over, although I am sure that he was very closely watching.

    Back at the ramp and standing outside the plane, my airspeed indicator was at 100knots and my altitude indicator was 1500 ft but the ramp is only 320ft. After a few minutes the pressure released and they indicated normally.

    What happened? The technician had checked my transponder and everything was fine. Afterward he noticed the static port tube was loose. He fixed the tube but failed to check it after fixing it. Holy crap sports fans.

    Scared me ****less. It was another few weeks before I was able to solo since I grounded my plane until properly repaired.
     
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  22. James331

    James331 Touchdown! Greaser!

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    FYI it's also mud dobber/ mud wasp season, check your pitots/static


    Always been a fan of having pre solo students do a few laps in the pattern with zero reference to the instrument panel.
     
  23. write-stuff

    write-stuff En-Route

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    Lost my airspeed indicator last week. Disconnected the pitot tube and blew it out with compressed are and all is well now.
     
  24. LongRoadBob

    LongRoadBob Line Up and Wait

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    I'm just curious, the failure on the 172, how did you know it was working normally above 50 knots? I'm a newbie, and my instinct would make me distrust the other readings if it falls to zero under 50. I would think possibly the pitot had partial blockage so when below some threshold it read the same as static because no air was getting in?
     
  25. LongRoadBob

    LongRoadBob Line Up and Wait

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    I carry a little flashlight to check (reading glasses on too) but on some pitot tubes it is very hard to see in the tube very far. Does it happen ever that something gets up in there, or is it almost always visible just at the opening?
     
  26. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    That's why there are pitot tube covers, yep, stuff (insects mostly) can get in there, and it may not be visible.
     
  27. LongRoadBob

    LongRoadBob Line Up and Wait

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    Thanks. I'm new to this, but guessing that if blocked further up, wouldn't one see abnormally low air speeds, or can it seem normal and later on stop up? Any slight blockage would always read low, correct? It would never cause it to read high?
     
    Last edited: Jun 26, 2016
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  28. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    A slight blockage may have no effect, or it could cause the indicator to be sluggish. A complete blockage in flight (extremely rare) could result in a higher than actual reading if you were reducing power in level flight and we're expecting to see a speed reduction. Don't ever blow anything into a pitot static port.
     
    Last edited: Jun 26, 2016
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  29. LongRoadBob

    LongRoadBob Line Up and Wait

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    Thanks. And of course you are right about not blowing air into the pitot. Took that dumb idea out of my post now.
     
  30. yakdriver

    yakdriver Cleared for Takeoff

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    I had a big bug hit the pitot on climbout one day and lost airspeed. Probably a one in a trillion shot. Don
     
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  31. Zeldman

    Zeldman Final Approach

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    It was my first flying job, working as an instructor. Cruise speed seemed normal for the power setting, as well as pattern speeds checked with power. Just when on final and slowing to land, as the A/S indicator hit about 55 it fell to zero. And you are right, it might not have been reading correctly.
     
  32. Norman

    Norman En-Route

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  33. GlennAB1

    GlennAB1 Ejection Handle Pulled

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    Sorry, can't "like" that, Norman!
     
  34. bobmrg

    bobmrg En-Route PoA Supporter

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    IMHO everyone should be able to land with the ASI covered. After I had been instructing for a while I began requiring at least one pattern without the ASI. I have experienced ASI failure twice..non-events both times.

    Bob Gardner
     
  35. BillTIZ

    BillTIZ En-Route

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    Standard pre solo maneuver with my students. Get off tow and hand them two intrument covers, one for the altimeter one for the airspeed. Figure out on drift down when it is time to enter a pattern and land.
     
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  36. BillTIZ

    BillTIZ En-Route

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    Pilot had complained that the ASI on one of our gliders was not reading correctly and reading lower than the tow plane while on tow. Much lower.

    The mechanic and I pulled the pitot line from the ASI and checked it was clear to the pitot, about 2 ft farther forward. We checked the static ports on the aft fuselage as best we could. No bug residue present. Time to put it back together and fly.

    On tow, cross checks with tow pilot, glider was about 20knts low and getting worse. By the time we reached 2K AGL, the ASI read 0. Off tow, fly pitch attitudes and sound. TLAR. Some approaches to stall to check reference attitude for approach with flaps at the landing position. No spoilers on this bird, just 90 degree flaps.

    On drift down to pattern and landing ASI increased to 80knts at pattern altitude and 120knts on landing. Ok, we have a blocked static problem. Before I could exit the glider, the airspeed wound down to zero. Ok, it's not a total blockage.

    Interestingly the altimeter shares the static, and behaved normally during the flight. Some lags and jumps, but it agreed with cross checks and read field elevation on landing.

    Unable to clear the blockage. Disconnect the static from the ASI which also opens the altimeter static to cockpit pressure. This is a standard configuration in many training gliders.

    2nd test flight, ASI is normal, no altimeter lags and jumps.

    We just got this glider airborne last month, it flew fine, no problems, and it did sit outside through a couple of hard rains last week. Checked with the previous owner, yes, when he left it out he would cover the static ports or he would have water in the static lines.

    100F temps this week, no rain forecast. It will dry out and then we'll keep the ports covered.

    And people wonder why we train glider pilots to fly traffic patterns and landings with no ASI or altimeter.
    Very few airplane pilots have that experience.
     
  37. Norman

    Norman En-Route

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    If there are any flexible rubber lines in the pitot/static system I'd be looking at them for internal deterioration. One little flap of rubber in one can wreak havoc with the system.
     
  38. steingar

    steingar Touchdown! Greaser!

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    Got bugs in the pitot tube when I had to tie down outside. Airspeed dead in takeoff, abort item and we shut down. Damn things. Lets hear it for hangars.
     
  39. RotorDude

    RotorDude Pattern Altitude

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    FTFY.
     
  40. SoCal RV Flyer

    SoCal RV Flyer Cleared for Takeoff

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    When you think about it, a hangar is just an extra-large pitot cover. :rolleyes: