FAA Advisory Circular 43.13-1B
Acceptable Methods, Techniques, and Practices
Aircraft Inspection and Repair
AC 43.13-1B | 2. Fabric Covering | 1. Practices and Precautions | 2-14. Inspection Rings and Drain Grommets
9/27/01
AC 43.13-1B CHG 1
on the bottom side of the wings except where
installed on the top surface by the original
manufacturer.
(1) Cutting the holes may be delayed
until needed; however, all covers should be
finished in matching colors with any trim lines
and stored until needed. Spraying matching
colors a year later is expensive and time con
suming.
(2) The 3-9/16 inch inside diameter
cellulose acetate butyrate (CAB) plastic in
spection access rings have become popular and
bond satisfactorily with Nitrate Dope or Fabric
Cement. Any metal inspection hole rein
forcements of a particular shape or special de
sign or size, installed by the original manu
facturer, should be reinstalled after cleaning.
(3) Tapes or patches over aluminum
reinforcements are optional, but recommended
in the prop-wash areas on the wings and for
ward fuselage bottom.
(4) Fabric patches over plastic rings are
strongly recommended because plastic is not a
stable material, becomes brittle at low tem
peratures, and fatigues and cracks from prop
blast vibration. Plastic rings are often cracked
during removal and installation of spring, clip-
held covers. Patches with a minimum 1-inch
overlap, should be installed with dope.
b. Drain Grommets. Atmospheric tem
perature changes cause the humidity in the air
to condense on the inside of aircraft surfaces
and pool in all low areas. Rainwater enters
through openings in the sides and top, and
when flying, everywhere throughout the
structure. Taxiing on wet runways also
splashes water up through any bottom holes.
Therefore, provisions must be made to drain
water from the lowest point in each fabric
panel or plywood component throughout the
airframe while in a stored attitude. Drain holes
also provide needed ventilation.
(1) Install drain grommets on the under
side of all components, at the lowest point in
each fabric panel, when the aircraft is in stored
attitude. Seaplane grommets, which feature a
protruding lip to prevent water splashes
through the drain hole, are recommended over
drain holes subject to water splashing on land
planes as well as seaplanes. The appropriate-
size holes must be cut through the fabric be
fore installing seaplane grommets. Plastic
drain grommets may be doped directly to the
fabric surface or mounted on fabric patches
then doped to the covering. Installing a small
fabric patch over flat grommets to ensure secu
rity is optional. Alternate brass grommets are
mounted on fabric patches, then doped to the
fabric.
(2) After all coating applications and
sanding are completed, open all holes through
flat drain grommets by cutting through the fab
ric with a small-blade knife. Do not attempt to
open drain holes by punching with a sharp ob
ject because the drain hole will not remain
open.
2-15.2-19. [RESERVED.]
Par 2-14
Page 2-23 (and 2-24)