Personnel conducting permeability tests should be alert to
anomalies in the color of the canopy fabric. Localized discolorations
are evidence of exposure to environmental contaminants. A change
in color shade from one (1) canopy section/surface to another is an
indication that the canopy may have been manufactured from
different lots of fabric. In either case, a permeability check should
be made on these areas of concern.
(2) For best results, the canopy should lie in an unpacked, unstressed condition for 24-hours
prior to testing. Care should be taken not to physically stress the canopy fabric during
handling and testing.
(3) Take a permeability reading in each cell of the canopy on the top surface (i.e. the MC-4 is a
seven (7) cell canopy so seven readings will be taken). Readings can be taken from either
sub cell. Readings should be taken approximately 18-inches aft of the leading edge nose
tape and should be roughly centered within the sub cell.
(4) If it is necessary to take a second reading within a cell, move to an untested area of fabric at
least 6-inches away (in any direction) from the location of the previous measurement.
(5) Calculate the average permeability of all readings recorded along the top surface nose
section of the canopy. Record this value.
(6) The desired average permeability for a new canopy manufactured with PIA-C-44378 (1.1 oz.)
fabric should be in the range of 0-5 ft.3/min./ft.2 (cfm).
(7) The maximum limit for a new, unused canopy is 6.0-cfm. Any new, unused canopy having a
permeability value of 6.0-cfm or greater will not be placed in service since its useful life can
be expected to be shorter than that of a properly manufactured canopy.
(8) During the service life of a canopy, if the average permeability along the top surface nose is
12.0-cfm or greater, the canopy will be immediately and permanently removed from service.
b. Procedure number 2. Measurement of Top Surface Cell Widths:
(1) This procedure requires use of a tape measure. Lay the canopy out spanwise on a clean
surface. Using approximately two pounds of tension, measure the nose tape span of each
cell along the top surface of the canopy, from loaded rib to loaded rib (see illustration below).
Loaded ribs are those which have V-tapes and line attachment points.
TOTAL TOP SURFACE SPAN
TOTAL BOTTOM SURFACE SPAN