I'm a few days away from my check ride, and took the plane I'm going to be in out for solo practice this morning. It's a PA-28-140. The panel was at some point replaced, and the new tach is digital (and eye level for the right seat). I've flown this plane before, though it had the "classic Piper" layout (analog tach by your knees) at the time.
Today I noticed the RPM drop when switching mags was just barely in spec, per the checklist - neither dropped anything close to 175 rpm (max allowed), but the left mag dropped about 90, and the right mag dropped about 48. Max difference between the two is 50 rpm, again, per the checklist.
I checked with the FBO mechanic and his response was "yeah, it's always done that, it's no bid deal." (The plane flies about 1000 hours a year, and goes up 2-3x/day.) I asked the FBO owner and he stated, "yeah, it's usually about 50-70 rpm difference, it always has been, but you only notice it now on the digital tach, the analog tach bounced around too much to ever see the difference."
I checked the POH, and it simply says: "Differential drop should not exceed 50 RPM while the total drop on either magneto should not exceed 175 RPM." (Emphasis added.) I.e., it's not mandatory ("may not"), just recommended.
I have no issues personally flying this plane exhibiting that behavior, because I know it and I trust it and the flight school / FBO. (Heck, I've personally logged about half my training hours in it, including 15 solo hours.) But will it be an issue with a DPE?
Today I noticed the RPM drop when switching mags was just barely in spec, per the checklist - neither dropped anything close to 175 rpm (max allowed), but the left mag dropped about 90, and the right mag dropped about 48. Max difference between the two is 50 rpm, again, per the checklist.
I checked with the FBO mechanic and his response was "yeah, it's always done that, it's no bid deal." (The plane flies about 1000 hours a year, and goes up 2-3x/day.) I asked the FBO owner and he stated, "yeah, it's usually about 50-70 rpm difference, it always has been, but you only notice it now on the digital tach, the analog tach bounced around too much to ever see the difference."
I checked the POH, and it simply says: "Differential drop should not exceed 50 RPM while the total drop on either magneto should not exceed 175 RPM." (Emphasis added.) I.e., it's not mandatory ("may not"), just recommended.
I have no issues personally flying this plane exhibiting that behavior, because I know it and I trust it and the flight school / FBO. (Heck, I've personally logged about half my training hours in it, including 15 solo hours.) But will it be an issue with a DPE?