11/212015 LET L 13-085a mandatory bUietin 

MANDATORY BULLETIN 

No. L13/985a 

Concerning: L13, L13A sailplanes 

Reason: On the L 13 BLANIK sailplane S/N 927226, the t ai lf uselage attachment fitting P/N A 192 921 N made of 

424253.11 material has been damaged in service . The material of this component must be tested as 

instructed in this Bulletin. 

To be accomplished 

To be accomplished 

Cost covered by: 

not later than: December 31, 1999 

by: The operator 

The operator 

Material availability: 

Validity: 

Total number of sheets: 

ing. Pesak I Manufacturer 

Upon the approval date 

5 

Engineering data contained in this Bulletin is CAl Approved . 

Date: November 17, 1999 

LET, a.s. , Kunovice 686 94, Czech Republic 

L13/985a Sheet 1 of 5 

==== 

A. WORK PROCEDURE 

1. Remove the oval cover located on the LH side of the fuselage , under the horizontal stabilizer. 

2.Test the material of the attachment fitting P/N A 192 921 N as 

follows: 

a)Conductivity measurement by means of eddy currents: - Recommended measurement frequency: 69 kHz - Probe diameter: not exceeding 15 mm - Measuring contact point: lower milled surface of the component, 

between the rivets (see, Figs. 1 and 2). 

Permissible range of measured values: 

X lACS: 28.5 - 35.9 

MS/m : 15.9 - 29 . 

Note: The surface protective coating of the component need 

not be removed. 

b) Hardness measurement by means of a portable digital hardness 

tester. Measuring method : depending on the type of the hardness 

tester used, i.e. dynamic, ultrasonic, and/or by means of a 

manual probe. 

Measuring point: lower milled surface of the component. 

Measured value: not lower than 199 HB. 

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11/212015 LET L13-085a mandatory bulletin 

c) Any other measuring method must be approved by the sailplane 

manufacturer before it can be used. 

3.1 If the values measured during the check are within the 

permissible limits specified above, make a record in the 

sailplane logbook (see section H of this Bulletin). The 

sailplane operation can be continued without any limitations. 

3.2 If the values measured during the check are not within the 

permissible limits, the attachment fitting P/N A 192 921 N must 

be replaced before the sailplane operation can be continued. 

4. If the attachment fitting P/N A 192 921 N is to be replaced, 

the operator shall place an order with the manufacturer, stating 

the sailplane Serial No., number of flight hours, registration 

mark, and number of its repairs and/or overhauls. 

5. The manufacturer will send to the operator the material 

required for replacement, together with a bulletin providing the 

work procedure. 

6. After the check, reinstall the inspection hole cover. 

L13/085a Sheet 2 of 5 

D. MATERIAL REQUIRED FOR MODIFICATION OF ONE SAILPLANE 

None. 

C. ILLUSTRATIONS 

Figs 1 and 2. 

D. DOCUMENTATION REQUIRED 

None. 

E. TOOLS REQUIRED 

Material hardness testing equipment: 

Eddy current conductivity meter 

Hardness tester 

F. SPARE PARTS IN OPERATION 

The spare parts in stock, if any, must be tested as 

instructed in Section A, item 2 of this Bulletin. 

G. SAILPLANE MASS 

Not affected. 

H. RECORD IN LOGBOOK AFTER BULLETIN IMPLEMENTATION L13/08Sa 

Attachment fitting P/N A 192 921 N material hardness 

tested. 

Measured values: 

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11/212015 

Sailplane 

Date: 

LET L13-085a mandatory bulletin 

cleared for operation. 

Carried out by: 

(legible signature of 

authorized engineer) 

I. ACCOMPANYING DOCUMENTATION 

Not affected. 

Contact Address: 

LET, a.s. 

Product Support Dept. 686 04 Kunovice 1177 

Czech Republic 

tel 0632/55 44 96; fax 0632/56 41 13 

E-mail: ots@let.cz 

L13/085a Sheet 3 of 5 

Sheets 4 and 5: 

Fig. 1 and Fig. 2 

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111212015 

LET L 13-0SSa mandatory bulletin 

L 13/085a Fig 1. and 2. 

Fig. 1 

Ffg. 2 

FuBe l age bulkhead N- lc with chment fitting P~ 

A 102 0 21 N 

SUPPLEMENT; 

http://home.nwi.net/-blanikamlball13-085a.htm 

f us&l age 

):)u tl F.·o <1. 

"1-1 . 14 

4f7 
11/212015 

LEl, a.s. 

686 04 Kunovlca 

C;r.e-ch Republlo 

OUfl;RII'J 

~~ /OTS!OO 

LET L13-085a mandatory bulletin 

f~ lETU. 

TO. OtANI I< AMERICA 

ATT.~ Vll~t~e srrol<y 

I'M: 00 1 !10!'1 llO.t.SlOG 

eouNYRY; WA , u.s.A. PAt'.£S: ~ 

MltT"Ar.T l>i;~tON: 

Josof fl~J/O'i'S 

Subj : LET Mandl!ltory Bulletin L 13IOB5a 

Either method is acc~ptable: 

A) Conduclivlty measurement by means of eddy curre~lts , or 

D) Hardness measuremcut by mean:; nf A portable digital hardneS$ tester. 

Equivalent material 

For those testing facilities which need to calibrate their measuring instrument by means of an equivalent 

U.S. material, below is the table provided by LET a.s. For clarity, the equivalent U.S. material is either 

CLAD 2024 T 351, or CLAD 2024 T3. 

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11/212015 LET L13-085a mandatory bulletin 

2) .t!spd Czech matertgl lur P/N A 102 011 'f:L 

Aluminium aloy Z 424253.62 

R- (~pt) = 407-:- 427 M..Pa 

R.p ( 0'0.?.) ~ 270 ..;-. 2 7 5 :MPa 

A = 11 _!_ 13% 

l!quivalent alloy Z 424253.61 

~(apt) ..-- 390 ~ 412 MPa 

~ (Cfo;) ~ 255 --=:.. 265 :\Ill' a 

A -= 10% 

temperature 

vr,..·.ater 

mne 

490 .... 505 oc 

20 ...L. 40 oc 

10 + 15 sec. 

ageing on the atr 5days 

3) U'S&, egu.tvalcnt mt;z,t~rtals 

aluminium alluy CL.AD 2024 T 351 

Rm ( Opl) =- 397 -t- 441 M:Pa 

~ (Go.:z) ~ 269 ~ 290 I'vl.Pa 

.. !J... = 4~ 12% 

equiV31ent <~lloy C:LAD 2024 T3 

Rw(~?t) _. 400 -:- 434 :MPa 

Rp (Go.~) ~ 269 .;,. 290 :VIPa 

... <\. ~tO+lS~i. 

heat treatement: 

PUBLIC SERVICE: 

tii!mperature 

watter 

495 ~ s (jc 

up to 3S :Joe 

There are many non-destructive testing facilities in North America. 

Some of them can be accessed at: 

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11/212015 LET L13-085a mandatory bulletin 

• NATIONWIDE http://www.nondestructivetesting.com/nav/aircraft.html 

• COLORADO. Terry or Robbie at: NDE Services Inc., 8775 East Orchard Road, Greenwood 

Village, CO 80111, Phone (303) 741-0518. Internet www.ndeseryjces.com 

• TENNESSEE. The man in Chattanooga, Tennessee, is Rich Hall. Phone number is 423 899 0043 

(W). 

• CALIFORNIA. Gail Flagor, g GE Inspection Services, 1211 K.ona Drive, Rancho Dominguez, Ca. 

90220, (310)635-2700 fax:(310)635-1646, Cell phone (310) 505-5648, e-mail: 

gail.flagor@ps.ge.com .They are in Compton, not a great neighborhood, but you can be in and out 

in a few hours .... 

• CALIFORNIA. Certified Testing and Consulting, 2100 Flight Line Drive #4, Lincoln CA 93648, 

Phone: 916.434.0195 

• MARYLAND. Maryland QC Laboratory, Don Wilson, Tel. (410) 575-7295, Fax (410) 272-5937 

• WASIDNGTON. Caliber Inspection, Seattle (at the Boeing Field) Tel. 800-638-3787 

• WASIDNGTON. 742 s. Spruce St. Burlington, WA 98233 ph 360 755 9350 

• PENNSYLVANIA. Precision Calibration in Yor~ PA. (717)840-4994. They have eddy current 

equipment as well as a machine to test the hardness ..... but the second one may be too large for this 

application. 

• MONTANA. The headquarters ofMontanaAnvil is 742 s. Spruce St. Burlington, WA 98233 ph 

360 755 9350. Their Missoula Mf address is Box 2336 Missoula, Mf 59806. ph 406 721 8803 

or 406 240 6134. The level III inspector that checked our glider is Brian Moran. The $233 GESC 

paid for this inspection included a prorated charge for travel from Missoula to Kalispell. Glacier 

Eagles Soaring Club 

• COLORADO. Leonard Lantz, Weststar Aviation, Grand Junction 800-255-4193. They can do 

conductivity test only. 

• NEW ENGLAND. Tailwind Inspections, Windsor Locks CT. 860-623-8600 will travel all over 

New England. (one customer paid $125 + $50/hr travel) 

............ END ........ 

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