Category: navion, fuslage
Applicability: All models
Supersedes: n/a
Compliance: Inspect as soon as practicable but not later than March 15, 1955
Procedure: Some Navion aircraft have been found to have cracks in fuselage frame 143-31004-16 at Station 294.1 inboard from the top stringer cutout at W.L. 21.00. Inspection may be made by removing the inspection plate on the left side of the fuselage beneath the horizontal stabilizer and looking forward to view the aft side of the points in question. If no crack is visible, no further immediate action is necessary, however, a thorough inspection of the frame at each 100-hour inspection will be required thereafter until the reinforcement indicated in item 2 or 3 as indicated below is completed. If a crack is visible at either side of the frame, determine if it has extended beyond the nearest rivet inboard of the cutout (hereafter called the critical rivet). If it has not, the repair as indicated in item 1 may be used as an interim fix in lieu of the permanent repair indicated in item 2 or 3 which is mandatory in the case of a crack extending beyond the critical rivet.
1. Interim repair for cracks not extending beyond the
critical rivet:
(a) When crack extends to the critical rivet, remove
the rivet and relocate nearby or if crack has not reached the critical
rivet, stopdrill end of crack.
(b) Install a modified diamond-shaped 0.125 24ST alciad
gusset to right and left outer fuselage surfaces catching two existing
rivets on each side of frame through W.L. 21 stringer, five existing rivets
through the frame above the stringer cutout and three existing rivets through
frame below the cutout. Add two AD4 rivets through the frame between the
three existing rivets below the cutout. Additional AD4 rivets through the
gusset and skin should be added as necessary.
(c) Check the cracked area at each 100-hour inspection
to determine if crack has extended beyond the critical rivet. If so, it
will be necessary to apply item 2 or 3.
2. Permanent Repair:
(a) Remove the cracked frame and strip off the angles
and doublers and attach to new frame. Do not notch new frame to receive
top
stringers.
(b) Cut top stringers forward and aft of frame location.
(c) Install new frame in fuselage and attach skin. Where
rivets do not properly fill holes use next size larger rivet.
(d) Secure top stringers forward of frame by adding a
0.040 245T alclad angle 3 inches long to the forward portion of the stringer
and attaching it to the frame flange with an existing AD4 rivet through
the frame flange, skin and external gusset patch.
(e) Install gusset patch as indicated in item 1(b). 3.
In lieu of item 2, an equivalent frame repair in accordance with CAM 18
will be accepted as an alternate for a new frame. This, however, may be
difficult due to the presence of existing doublers and stiffeners on the
forward face of the frame which is further complicated by the attachment
of the W.L. 21 shear web to the aft side of the frame. Such alternate repairs
must be submitted to a FAA Aircraft Engineering office for approval prior
to installation.
Notes: Ryan Field Service Bulletin No. 22 covers this same subject.
AD-55-01-01