AD 77-15-05

77-15-05 LET N.P.: Amendment 39-2974. Applies to Blanik 13 gliders, certificated in all categories, with serial numbers 173205 through 174230, inclusive.

Compliance is required as indicated.

To prevent structural failure of the fin top rib, accomplish the following:

(a) Within the next 10 hours time in service after the effective date of this AD, unless already accomplished within the last 90 hours time in service, and, thereafter, at intervals not to exceed 100 hours time in service from the last inspection, visually inspect the fin top rib and central stiffener (fuselage stiffener) with a 5 power magnifying glass in accordance with the accomplishment instructions set forth in paragraph A of LET N.P. UH HRADTSTE-KUNOVICE (LET N.P.) Mandatory Bulletin No. L13/040, undated, or an FAA-approved equivalent.

(b) If cracks are found in the fin top rib of less than 5 mm in length, or of any length in the central stiffener, before further flight, either -

(1) Repair the fin top rib or central stiffener as necessary, in accordance with the accomplishment instructions set forth in paragraph B of LET N.P. Mandatory Bulletin No. L13/040, undated, or an FAA-approved equivalent; or

(2) Comply with paragraph (e) of this AD.

(c) If any cracks are found in the fin top rib which exceed 5 mm in length, before further flight, comply with paragraph (e) of this AD.

(d) If no cracks are found, within the next 200 hours time in service after the effective date of this AD, comply with paragraph (e) of this AD.

(e) Replace both the fin top rib and central stiffener in accordance with the accomplishment instructions set forth in paragraphs C and D of Let N.P. Mandatory Bulletin No. L13/040, undated, or an FAA-approved equivalent.

NOTE: To assist in the dismantling of the rudder the following information is provided:

(1) It is recommended that, in loosening the split pin securing the slotted nut in the bottom rudder hinge, the bent ends of the split pin be straightened first using a suitable pointed tool and then the pin be removed.

(2) The rudder dismantling procedures are as follows:

(i) The nut of the bottom rudder hinge accessible through the mounting opening on the fuselage part should be released and unscrewed.

(ii) The cloth blinds on the rudder edge curve and leading edge should be removed. The top rudder hinge stud bolt should be released and unscrewed.

(iii) The rudder should be lifted slightly and its top edge should be pulled slightly backwards to be released from the top hinge.

(iv) The rudder should be held in the inclined position and carefully lifted from the step ball bearing.

(3) The bottom rivets of the intermediate stiffener supporting the rudder bearing should be routed by an extended drill rod through the 60 mm. diameter opening in the rear fuselage partition as recommended by the Note in paragraph D of LET N.P. Mandatory Bulletin L13/040. Routingof the rear fuselage part in position 14 of the partition is not recommended.

(4) A modified shank should be used for riveting a new fin rib. For this purpose, a 35 mm. diameter opening should be made in the fin spar (See LET N.P. Mandatory Bulletin L13/040, paragraph C).

(f) The inspections required by paragraph (a) of this AD may be discontinued when the fin top rib and central stiffener have been replaced in accordance with paragraph (e) of this AD.

This amendment supersedes Amendment 39-2333 (40 FR 33007), AD 75-17-28, as amended by Amendments 39-2379 (40 FR 45802) and 39-2498 (41 FR 2375).

This amendment becomes effective August 4, 1977.