10-24-2011 Ask Mike! Archive
Dorne and Margolin antenna installation?

I am working with a customer that wishes to install the Dorne & Margolin N4-17 VOR Glideslope antenna. 

I have been talking with the local FAA about the installation that Robert Siegfried has shown on the Bonanza.org and they are wanting to get a DER involved as to approved data. 

Looking at the last entry on the post (editor's note:  referencing forum thread from bonanza.org) you mentioned you had installed these antennas in the past and am wondering if you have a description available for the installation of doublers without the cross bracing available.

Jeff T.

Jeff;

This was done, as others in the past - whether D&M or Comant antennas - by log book entry only.  Our local feds are constantly changing how they desire paperwork on the avionics themselves, but the antennas are pretty clear.  As 43.13 discusses antenna (and doubler) installations, this is good information.  However, don't confuse the idea that if it came from 43.13 it has to be 'major'.

By definition, "major alteration":  (from FAR 1)
    This does not affect the weight and balance envelope of the aircraft - same limits apply
    Structural strength and flight characteristics are unchanged if the doubler ties into structure properly and the antenna is parallel to the WL
    Performance and powerplant operations are NA
    Accepted practices - Part 43 and 43.13
    Elementary operations:  Probably the only gray area; what is elementary for a 30+ year sheet metal man is not for a green A&P.

I look at this as a minor alteration, log book entry only.  Do not simply install a scab of aluminum as a large area washer; think it out, tie it in to structure, I recommend one increment thicker than the skin, that data is in the skin plating diagram in the Shop Manual.

Mike

Appreciate the response.  On your doubler do you catch the stringer or do you stay inside the stringers on bulkhead.  Could you give me an idea of the size of your doubler?

Attached photo with comments inserted.  Apologize for the quality of the photo; I took it this afternoon and on my way back from storage hangar to office I dropped the camera, so taking another and using it is, unfortunately, out of the question until I replace some optics.  But, it should give you the general idea.

Much appreciated.