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Old 06-24-2018, 10:40 AM
Tankerpilot75's Avatar
Tankerpilot75 Tankerpilot75 is offline
Join Date: Jan 2015
Location: Oklahoma City, OK
Posts: 586
Default Altimeter check Question

I?m seeing something that totally confuses me when I do my altimeter check prior to takeoff. I have two EFIS systems (1) a GRT Horizon WS as my primary and (2) a Dynon D10A with internal battery as my backup.

Lately on the first flight of the day my GRT system indicates an altitude of around 50 to 60 feet of actual field altitude once I set in the current altimeter setting. The Dynon is always within 15 to 20 feet. Since both are within 75 feet of field altitude I note the difference and continue. However, as the day progresses and I fly multiple flights (usually second flight of the day is a YE Flight event) I notice the altimeters are more closely aligned and within 10 to 15 feet of field altitude and also each other. Subsequent flights again stay within this 10 to 15 foot agreement.

The aircraft had its altimeter/transponder check done last summer and hasn?t been touched since. Any ideas as to what is occurring?
Jim Harris, ATP, T38, EC/KC-135A/E/R, 2008 RV7A, 2nd owner, N523RM (2015)
Superior XPIO-360, Hartzel CS prop, Aerotronics panel with Dual GRT Horizon WS, EIS, Garmin 340, 335 w/WAAS gps, Dual 430s (non-WAAS), TruTrak 385 A/P with auto-level, Electric trim, Tosten 6 button Military Grips, FlightBox wired to WS, Dynon D10A w/battery backup, 406 MHz ELT. Custom Interior, New TS Flightline hoses, Great POH!
Retired - Living the dream - going broke!
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Old 06-29-2018, 05:36 PM
JPalese's Avatar
JPalese JPalese is offline
Join Date: Apr 2011
Location: KHXF
Posts: 143
Default Altimeter Calibration

I'd send GRT support an e-mail asking their thoughts.

Do you know if the altimeter calibration routine was ever done on the WS?

The altimeter calibration routines are in the WS manual.

John Palese
1) AAL Captain & Check Airman (ret)
2) USAF LtCol & Command Pilot (ret)

2) Adjunct Professor-Aviation Science
3) MKE FSDO FAAST Lead Rep & Remedial Trainer.

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