Hello José,
No problem! When you have set your airport altitude to e.g. 226 m in Google Earth you kan open the kml-file with notepad within FSX_KML and manually change the values to, in my case, 225.86. Remember to change all relevant values. Save and build.
Of course, if you want the value to be 13 feet you will have to convert to metric value first!
Like this!
From:
<description>Airport_Backgrounds_Flatten_MaskClassMap_ExcludeAutoGen</description>
<styleUrl>#m_ylw-pushpin_copy54</styleUrl>
<Polygon>
<tessellate>1</tessellate>
<altitudeMode>absolute</altitudeMode>
<outerBoundaryIs>
<LinearRing>
<coordinates>
14.06194608202101,57.74651292480915,226
14.06437329319439,57.74640631527953,226
14.0646307675717,57.74644904882966,226
14.06478734068034,57.746600367777,226
.....................................
To:
<description>Airport_Backgrounds_Flatten_MaskClassMap_ExcludeAutoGen</description>
<styleUrl>#m_ylw-pushpin_copy54</styleUrl>
<Polygon>
<tessellate>1</tessellate>
<altitudeMode>absolute</altitudeMode>
<outerBoundaryIs>
<LinearRing>
<coordinates>
14.06194608202101,57.74651292480915,225.86
14.06437329319439,57.74640631527953,225.86
14.0646307675717,57.74644904882966,225.86
14.06478734068034,57.746600367777,225.86
.........................................
Good luck!
Erik