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(8.) Sealing Holes and Voids (Figure 205)
Voidsare defined as gaps between airframe members which present a direct opening through the pressure vessel structure. Such gaps occur at stringer cutouts in the pressure bulkheads,forming reliefs and flanges. Holes and voids which are less than 0.125 inch wide must be filled with sealant, building up a bead with a minimum thickness of 0.062 inch. If the gap is larger than 0.125 inch wide, use a mechanical closure such as a soft rivet, a screw and washer. If rivets are used, be sure to brush coat both sides with class A-1/2 sealant.
(9.) Holes and Voids in (Cold) Air Duct Work (Figure 205)
Sealing in this area prevents air noises and eliminates undesirable, uncontrollable drafts. Apply sealant to any holes and voids less than 0.125 inch wide. Apply 3M 471 plastic tape on inside or outside surface of any holes and voids larger than 0.125 inch.
EFFECTIVITY:

040-999
51-20-00PAGE
Jan 7

10/90
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A. Processes(continued)
FayingSealBetweenSkinsat Skin Lap Skin Skin
an 10/90
PIPERAIRCRAFT
PA-42-720 (Advanced Trainer)
MAINTENANCEMANUAL

A. Processes(continued)
1.
Bulkhead

2.  

Fayingseal

Pressure Side
3.
Stringer

4.
Skin

5.
Stringer seal plate

6.
Brush  coat with ClassA-1/2sealant

7.  

Filletseal

8.
Bulkhead cutout

14
SEALING HOLES
9.  

Fuselageskin

10.Faying  seal at forward bulkheads between skin and stringer
11.Bulkhead flange
12.Screw
13.Seal plane (skin, bulkhead, etc.)
14.Large hole (greater than .125")

15.Nut
SEALINGSTRINGERS 16. Washer

Stringers, Holes and Voids Seals
Figure 205

Apply Sealantwith Flow Gun
D

View A
Applicationof Fillet Seal
ViewC
Dimensions

Press Sealant into Place
with Fairing Tool

D = 0.10" Min.
W = 0.20" Min.
A + B = W, Except A = 0 when

B = 0.20" or More

View B
Forming of Fillet Seal

Fillet Seal
Figure 206

EFFECTIVITY:
040-999
51-20-00an10/90

PIPER AIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCE MANUAL

A. Processes(continued)
1. SealingProcedures(continued)
(b) FuselageSealing (continued)
(10.)SealingSeamsandJoints (Figure 206)
Fillet seals must be used along edges of all structures rivettedtothe skin in the pressurizedarea,such as frames, stringers,doublers, laps, seams, and joints. Apply sealant with a pressure gun and be sure to avoid getting gaps or bridges along the seam joint. Final dimensions of a cross section of bead must conform to those shown in Figure
206.
CAUTION:  ENSURE PRESSURE GUN CONTAINSENOUGHSEALANTTO COMPLETEA SEAL AT ONE INJECTION WITHOUT ANY BREAK. STOPPINGAND STARTING CAUSES AIR BUBBLES IN SEALS AND WILL PRODUCE A POOR SEAL.
(11.) Sealing Fasteners (Figure207)
Seal all fasteners installed in a seal plane by filleting around fasteners,after installation, with a coat of B-2 class sealant.
NOTE: If a bolt or nut is being sealed, it must be torqued before sealants set. Tightening after sealant sets is not recommended.
(12.)Sealing"AN"StandardBulkheadFittings
SealAN fittings passing through pressure plain of the bulkhead by cleaning aroundseal area. Apply sealant to inside surface around the hole and install the fitting before the sealantsets.
0.06"
Bolthead
.005 to .015'

Bolts and Rivets Seals
Figure 207

EFFECTIVITY:
PIPER AIRCRAFT PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

A Processes(continued)
1. Sealing Procedures (continued)
(b) FuselageSealing (continued)
(13.)SealingElectricalHarnesseswith sealing compound (Figure 208)
Thesesteps pertain to the main fuselageand wing harnessonly. The wire harnesses are
sealedat the point where they pass through the pressure bulkhead.
(a.) Clean area of bulkhead where seal fittings will seal.
(b.) Pass wire bundle through hole provided in bulkhead.
(c.) Place sealfitting halves aroundwire harness, on pressure sideof bulkhead.
(d.) Fill groove in mounting flange of the fitting halves with sealant. (Refer to view A of

Figure 208.)

NOTE: Use enough sealant to assure it extrudes around the mounting flange after securingthemto the bulkhead.
(e.) Secure fitting to bulkhead with fasteners. (f.) Fillet seal extrudedsealant around sides of mountingflange (shown in view B of Figure 208). (g.) Put nozzle of sealant gun in center of wire harness and work sealant throughout wires inside seal fitting (shown in view C of Figure 208). (h.) Place a strong piece of string against the seal assembly,parellel with the wires. (Refer to view D of Figure 208.) (i.) Wrap fittinghalves with threeturns of 1.50 inch wide maskingtape. (Refer to view D
　
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