To All (trying again) I often get calls from people regarding instruments and these often involve TE problems as well as head/tail winds which seem totally wrong.
With TE I suggest you check the TE line from fin to panel for a PARTIAL blockage. People do a leak check but this does not check the line for partial blockage. My simple field method is remove ALL instruments from panel end and then very sharply suck with your mouth at TE end and you may feel there is a restriction. To be sure I compare this with a 5m (say) coil of 6mm instrument tube and suck the same way. Tom Gilbert uses another method. You can easily pick the difference. Usually the partial blockage is at the TE end (tube has been left off and hole has been visited by a hornet!). Ideally clear the obstruction mechanically and it is usually only in 20cm from TE socket. Back blow out the tube (NOT WITH COMPRESSOR). If available use either fish tank air pump. If that fails I use a SMALL sip of water in my mouth and back and forward and suck the mess into my mouth. You may have to dry out the tube. With head wind tail wind problems most instruments will have a digital ASI reading and this should be checked to the WInter ASI at about 80KTS. The digital ASI should be within say 2 (to 3) kts of the Winter. If not then something should be done and in the case of LNAV read page of the Manual and if really bad (more than 40 counts) then it may have to be sent in for service. Head/tail information will be all over the shop if you have a problem there as 4kts digital ASI error can make a big error in Head/tail wind information . While on instruments Mechanical ASIs can have a partly blocked Pitot or even a blocked static without the owner realising. This show up in a DI but takes 2 people and the ASI should IMMEDIATELY return to zero after a terst. When flying a partly blocked ASI can show up as higher than normal ASI when climbing and when descending the ASI will be lower than normal. If you pull out airbrakes ASI indicator may go to well below stall!!!!! There is a message there. Most people doing an annual inspection get out their manometer and check JUST the ASI. In my experience ASI are reasonably accurate -the problems are usually elsewhere. Each year I seem to hear a story of an ASI being damaged in this manometer exercise. For years I have used a new mechanical winter and recently discovered Ian Patching (RTO/Airworthiness Vic Tas) uses a trusted ASI which I guess he checks once a year. I could only recommend this method as I hate to tell people it is going to take Eur100+ to have and ASI repaired. Having said that I could recommend each 20 to 30 years Mechanical varios and maybe ASIs go back to WInter in Germany for service and in the case a Winter varios they will come back BETTER than new!!!! New faces for instruments are relatively inexpensive and you then have a "mutton dressed up as lamb" instrument It is always worth checking for leaks in the system but there is more. I have other ideas on instruments installs and potential problems which I have talked to people over the phone over the years. Even the German Glider Factories are not necessary perfect on their installs!!! I have to admit most people are not reporting they forgot to change their internal battery in their Model 20 logger and the LNAV so seems the message has got out there!!!! Anyhow happy flying with everything working in your panel Ian McPhee 0428847642 Skype <macca304>. .
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