EFFECTIVITY: 040-999

Jan10/9051-10-00
PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

4. Cracks in Bend Radius Areas)
of Flanges(Non-Pressurized
(a)When a flange has a crack lessthan 1/4 inch long, repair the crack by grinding itout smoothly while maintaining a inch radiusat the base of the crack.
(b)Whena flange has a crack greater than1/4 inch long, but not exceedingoneinch in length,andthe crack is located at the end of the flange,proceedas follows: (1.) Stop drill the crack(specifiedinChart801). (2.) Install an angle stiffenerof the samematerial, thickness, heattreat,finish,and sufficient
lengthto pick up two additional rivetsbeyondthe end of the crack.
NOTE: Both legs of the angle musthave the same number of rivets. When installingrivets,use the sametypeand size asthe existing rivets.
(c) A flange having a crack whichdoes not exceedoneinch in length, and which is not locatedat eitherendof the flange,can be repairedasfollows: (1.) Stop drillthe crack at both ends (specified in Chart 801). (2.) Install anangle stiffener of the same material, thickness,heattreat, and finish as the
originalflange.Thisstiffenermustbeof sufficient.length rivets
to pick up two additional beyondthe end of the crack at both ends.
NOTE: Bothlegs of the angle must havethe same numberof rivets. The rivets used mustbe of the sametype and size as the existing rivets.
(d)Cracksinflanges having four rivets or less, mustbe repaired as follows: (1.) Cut off flange to remove the crack. Replacewith an angle of the same material,thickness, heat treat, finish,andcontour.
(2.) Attach repair angle with two rivets in the webfor every one rivet in the flange.Rivetsmust be of the sametypeand size as the existing rivets.
5. Cracksin Flange
(a)A short crack in a flange originatesat the flange edge does not extend beyond the line mid-way betweentheedge and the band tangentline,and is more than 2D (twice the nominaldiameter of the rivet) from the rivet holes. Do not use this repair within two rivets from a splice. (1.) Stop drill as specifiedin Chart 801. (2.) Add a patch plate of the same materialandthicknessas the flange.
NOTE: Radiusonecomerof the plate to providea snug fit into the bend radius.
(3.) Attach plate with the numberandsize rivets shown in Chart 802.
NOTE:The number shown is the number of rivetson each side of the crack. Should the crackbe between the second and third rivet from theend of the flange, the two end rivets canbe used andthe number willonlyreferto the rivets requiredon the
remainingside.
EFFECTIVITY: 040-999
51-1000
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51-10-00 Jan 10/90

PIPERAIRCRAFT
PA-42-720(AdvancedTrainer)
MAINTENANCEMANUAL

5. Cracksin Flange (continued)
(b) Short cracks to rivet holes include those within 2D from a rivet hole. (1.) Stop drill (specified in Chart 801) those cracks which do not terminate at a rivet hole. (2.) Add a patch plate of the same materialand thickness asthe flange. Radius one corner of
theplate to provide a snug fit into the bend radius. (3.) Attach the plate with the number and size rivets specified in Chart 802.
NOTE: Midspace one rivet that is one diameter less than originally used (minimum size is 3/32inch diameter) on each side of cracked hole.Maintainedge distances and spacing.
(c) Longcracks originate atthe flange edge and extend beyond the flange centerline,not extendingintothe bend radius. (1.) Stop drill the crack as specified in Chart 801. (2.) Add an angle of the same material and thickness as the flange. The legs of the angle
mustbe of equal length. Thenumberand size of the rivets to be used are found in Chart
802.
NOTE: Both legs of the angle must have the same number of rivets. If the stop drilling producesa double line,or if the stop drilling is within 2D of a rivet hole,add a midspacedrivetone diameter smaller(minimumdiameter3/32 inch) on each side of the affectedhole.
CHART 801
STOPDRILL SIZES

MATERIAL THICKNESS DRILL SIZE
Upto .032 #50 (.070) .040to .064 #40 (.098) .072to .081 #30 (.129)
CHART 802 NUMBERAND SIZE OF AD RIVETSREQUIREDON EACHSIDE OF CRACKS
WIDTHOF FLANGE
UP TO .50 (Inch) .50 TO .75 (Inch) .75 TO 1.00 (Inch)
MATERIAL RIVET NUMBER RIVET NUMBER RIVET NUMBER THICKNESS SIZE REQUIRED SIZE REQUIRED SIZE REQUIRED
3/32 3 3/32 4 3/32 5
UPTO .040 (inch) 1/8 3 1/8 3 1/8 4 5/32 2 5/32 3 5/32 3
1/8 4 1/8 4 1/8 5 .051TO .064 (inch) 5/32 3 5/32 4 5/32 4
EFFECTIVITY:
040-999

PAGE6 51-10-00
51-10-00
Jan10/90
PIPERAIRCRAFT
PA-42-720(Advanced Trainer)
MAINTENANCEMANUAL

6. Cracksin Lightening HoleFlanges
(a)
Ifthe crack length does not exceed fifty percent of the distancebetweentheedge and the bend radiustangentline,the crack can be fairedoutgraduallywith a minimum radiusof inch.
　
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