Altimeters and Encoders

[Bob Turner]

Some years ago one of my students proudly stated he cruises at the altitude shown on the face of his Garmin transponder. A local pilot told me he was flying GPS altitude, and he felt that his altitude was more accurate than others.

Today during a flight review my student explained that he flies 200' high on his (properly set) altimeter so ATC gets the proper readout.

Instructors - stress this (along with not blocking runways and not blowing dust into others' hangars):

The only accurate source of altitude information in the cockpit is the altimeter. If you use any other source, you are reducing vertical separation and compromising safety. The altimeter may not match your actual linear altitude, but it does represent pretty much the same info that others in the same airspace are using. Altimeter settings put all aircraft on the same reference, accurate or not.

 

[Hiperbiper]

One Caveat;
It doesn't hurt to occasionally check the accuracy of your altimeter on the ground using a current Barometric Pressure and the airport elevation. Altimeter readings are based on a properly adjusted instrument and while they are adjustable to a point it is not legal for anyone save an instrument shop to do so...
So check you altimeter and if you find it grossly misreading send it off for IRAN.
Just my .02
Chris

 

[Bob Turner]

I do that every day. Not the IRAN part, of course. And I would never, ever touch that set screw!

 

[Hiperbiper]

I do that every day. Not the IRAN part, of course. And I would never, ever touch that set screw!

Not even just a iddy biddy bit?

 

[BB57]

Checking that the altimeter, with the correct current reported altimeter setting in the Kollsman window, shows the correct altitude within 75 ft is more or less an FAA requirement. If there is an error, setting it to the actual field elevation and noting the setting in the Kollsman window and comparing that to the reported altimeter setting will give you a good idea of the error that is present. For example of the altimeter setting is 29.92 and you need 29.96 to get the actual field elevation that +0.04 difference will be fairly consistent inflight as well.

——

The regs require that little adjustment screw only be adjusted by a certified repair station. The FAA no longer allows an A&P or even IA to make the adjustment.

I won’t mention that my certified repair station showed me how to make the correction should the need ever arise or that he suggested it’s not rocket science.

Let‘s for sure not get into the legalities of who can or cannot swing a compass…

 

[Bob Turner]

It would be truly dumb to admit it, either here or in a logbook.
Ever swing a compass? I tried it once - you really need a turntable. Better and more accurate to do it in flight with a gps on a very calm day.

 

[Hiperbiper]

I've always done the "air swing" compass adjustment...lots of razor straight section lines around here.
It's funny the number of times an aircraft owner questions the requirement for a compass correction card to replace the one that turned to dust 10 years ago...
Chris

 

[Bob Turner]

You have to have one. Checkrides get cancelled when they are missing. Nobody ever reads them.