I know that if VSI shows +100 during preflight cockpit check that can be considered as 0 and flight can be conducted based on that but what is the max error permissible for VSI usage.

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    $\begingroup$ The VSI is not a required instrument for VRF or IFR flight and unlike the altimeter, there are no tolerances specified in Part 43. There is no max error so you just need to compensate in flight. Mine is old and was showing an error of 50' on the ground. My A&P adjusted it but it still shows 10 climb during runup. In level flight it will show a slight climb. $\endgroup$ – JScarry Oct 20 '19 at 14:33
  • $\begingroup$ @JScarry this is probably enough for an answer! $\endgroup$ – Quentin H Oct 21 '19 at 14:32
  • $\begingroup$ thanks @JScarry, actually i know that VSI is not a required instrument, but recently we were talking about preflight cockpit check with my instructor and he insisted that there is a max permissible error for VSI. Also he gave me this as a homework assignment but I couldn't find it anywhere that is why I asked here. $\endgroup$ – knightRider Oct 21 '19 at 15:07
  • $\begingroup$ @knightRider There is no limitations for VSI in the FARs. The FARs have four that I am aware of. Transponder and ADSB for all aircraft and VOR and pitot static/altimeter for IFR. Even the compass has errors, that’s why you have a compass correction card—but when you swing the compass you try to minimize the errors. Otherwise it is up to the pilot whether to accept errors. e.g. my manifold pressure is low by 1 inch and my prop RPM is low by 150 RPM. We make a mental adjustment while flying. We have never had the airspeed indicator checked and I doubt that after 43 years it is accurate. $\endgroup$ – JScarry Oct 21 '19 at 17:10

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