N A T I 0 A AIRCRAFT ACCIDENT REPORT I L T R AIR IOWA .

- 4 -ANALYSIS AND CONCLUSIONSThe o u t e r p a n e l of t h e r i g h t wing f a i l e d i n f l i g h t and r o t a t e d upwardapproximately 115O b e f o r e t h e a i r c r a f t s t r u c k t h e ground, which confirmst h e statement of w i t n e s s e s t h a t t h e r i g h t wing folded upward i n f l i g h t .M e t a l l u r g i c a l examination o f t h e r i g h t wing t u b u l a r lower s p a r cap showedt h a t t h e wing f a i l u r e was caused by a f a t i g u e f r a c t u r e i n t h e lower s p a ra t Right WS 81.This was t h e f i f t h f a t a l a c c i d e n t s i n c e June 1964 t h a t involved wingf a i l u r e i n Beechcraft Model 18 a i r c r a f t r e s u l t i n g from a f a t i g u e f r a c t u r e a tWS 81. A l l o f t h e s e wing f a i l u r e s occurred i n areas where i n s p e c t i o n sdesigned t o d e t e c t f a t i g u e c r a c k s were r e q u i r e d by Airworthiness D i r e c t i v e s .Again, t h e problems i n d e t e c t i n g f a t i g u e c r a c k s d u r i n g t h e s e r e q u i r e d inspect i o n s a r e c l e a r l y demonstrated i n t h i s a c c i d e n t . Examination by t h e S a f e t yBoard of t h e X-rays taken during t h e i n s p e c t i o n s on May 12, 1967, J u l y 7,1971, December 14, 1971, May 25, 1972, October 26, 1972, and March 31, 1973,i n d i c a t e d a c r a c k a t R i g h t WS 81. However, t h e c r a c k i n d i c a t i o n had n o tbeen d e t e c t e d by t h e personnel a u t h o r i z e d t o perform t h e s e i n s p e c t i o n s ,e i t h e r through examination o f t h e X-ray f i l m s o r by t h e o t h e r means f o ri n s p e c t i n g t h e s p a r s p e c i f i e d i n t h e Airworthiness D i r e c t i v e s . The Boardnoted an i n d i c a t i o n o f t h e c r a c k which caused t h e f a i l u r e a t R i g h t WS 81on t h e X-ray f i l m d a t e d May 12, 1967. Although t h e c r a c k was n o t r e a d i l yi d e n t i f i a b l e as a f a t i g u e c r a c k , i t was n e v e r t h e l e s s v i s i b l e and shouldhave prompted concerned personnel t o make a more thorough i n s p e c t i o n o ft h e a r e a . The f a t i g u e c r a c k was i d e n t i f i a b l e , however, on t h e X-raysd a t e d J u l y 7 , 1971, and on a l l subsequent X-ray photographs taken fromJ u l y 7, 1971, t o t h e d a t e of t h e a c c i d e n t . During t h a t p e r i o d , t h e f a t i g u ec r a c k a t Right WS 81 should have been d e t e c t e d by any one o r a l l t h r e emethods approved f o r i n s p e c t i o n : v i s u a l , magnetic p a r t i c l e , and X-ray.The S a f e t y Board concludes t h a t t h e concerned r e p a i r s t a t i o n s d i d n o tcomply w i t h t h e wing s p a r i n s p e c t i o n procedures p r e s c r i b e d i n t h e a p p l i c a b l ea i r w o r t h i n e s s d i r e c t i v e s and t h a t q u a l i t y c o n t r o l of t h e i r i n s p e c t i o nprograms was p r a c t i c a l l y n o n e x i s t e n t . A s a r e s u l t , t h e a i r c r a f t was flownw i t h a d e t e c t a b l e c r a c k i n t h e e l l i p t i c a l tube of t h e lower main s p a r a tRight WS 81 u n t i l t h e c r a c k became l a r g e enough t o cause complete f a i l u r e .Furthermore, t h e r e are no w e l l - d e f i n e d s t a n d a r d s f o r c e r t i f y i n g a r e p a i rs t a t i o n a s a r a d i o g r a p h i c f a c i l i t y o r f o r q u a l i f y i n g a t e c h n i c i a n f o r nondestructive testing.The S a f e t y Board recognized t h e s e d e f i c i e n c i e s e a r l y i n t h e i n v e s t i g a t i o n and recommended t o t h e Administrator t h a t t h e FAA t a k e a d d i t i o n a la c t i o n s t o a s s u r e t h e continued a i r w o r t h i n e s s of t h e s e a i r c r a f t .

- 5 -PROBABLE CAUSE3rdS:dIIc%:e at11,.973,I!iI 1i.dRECOMMENDATIONSi ives.]specFetyThe National Transportation Safety Board determines that the probablecause of this accident was the in-flight failure of the right wing whichresulted from a preexisting fatigue crack in the lower spar cap of the wingat Wing Station 81. Although the fatigue crack existed and was discernibleduring inspections conducted over the 6-year period prior to this accident,it was not detected.As a result of the investigation of this accident, the Safety Board,on April 25, 1973, issued three recommendations (Numbers A-73-16 through 18)to the Federal Aviation Administration that were intended to increase thesurveillance and quality control of all inspections made to ensure detectionof fatigue cracks in the wing structure, to incorporate one of severalapproved kits to reinforce the wing spars on all models of this aircraft,and to consider the practicability of licensing aircraft radiographictechnicians. Copies of the recommendation letter and the Administrator'sresponse thereto are included in Appendix C.BY THE NATIONAL TRANSPORTATION SAFETY BOARD.gueJOHN H. REEDChairman/S/n.ot.c ableFRANCIS H. McADAMSMemberLOUIS M. THAYERMember.owntlre.r/s/ISABEL A. BURGESSMember/s/WILLIAM R. HALEYMember10n-October 3, 1973

- 7-APPENDIX ACREW INFORMATIONCaptain Charles E. Nixon, aged 3 7 , held Airline Pilot CertificateNo. 1453010 with flight instructor and commercial privileges in singleand multiengine land aircraft. He held an FAA first-class medicalcertificate, issued on February 2 3 , 1 9 7 3 , with no limitations.He had accumulated a total of approximately 6,000 flight hours, ofwhich 2,000 were in the Beechcraft Model 18; 247 hours were flown inthis make and model within the preceding 90 days. According to FAA andto the operator's records,Nixon was certificated and currentlyqualified in compliance with applicable Federal Aviation Regulations.Mr.,

- 8 -APPENDIX BAIRCRAFT INFORMATIONBeech A i r c r a f t Model E18S, N310WA, S e r i a l No. BA- 12, had accumulateda t o t a l of 11,339 hours of f l i g h t . The l a s t annual i n s p e c t i o n wasaccomplished on J u l y 11, 1972, and t h e No. 4 i n s p e c t i o n of A i r Iowa’sapproved i n s p e c t i o n p l a n , on A p r i l 1 3 , 1973. The a i r c r a f t had flownapproximately 16 hours s i n c e t h e No. 4 i n s p e c t i o n .With t h e e x c e p t i o n of t h e i n s p e c t i o n s d i s c u s s e d i n t h e t e x t o f t h i sr e p o r t , t h e a i r c r a f t had been maintained i n accordance w i t h t h e F e d e r a lA v i a t i o n Regulations.The wing e l l i p t i c a l f r o n t s p a r lower cap had been i n s p e c t e d w i t h i nt h e p r e s c r i b e d 500-hour f l i g h t time i n t e r v a l s on March 21, 1973, October 26,1972, May 24, 1972, December 14, 1971, and July 7, 1971.No c r a c k s were d e t e c t e d d u r i n g t h e s e i n s p e c t i o n s .

- 9-APPENDIX CUNITED STATES OF AMERICANATIONAL TRANSPORTATION SAFETY BOARDWASHINGTON, DL.ISSUED:A p r i l 25,1973Adopted by t h e NATIONAL TRANSPORTATION SAFETY BOARDa t i t s o f f i c e i n Washington, D. C .on t h e 23rdday of A p r i l 1973SAFETY RECOMMENDAT IONS-4-73-16 t h r u18The N a t i o n a l T r a n s p o r t a t i o n S a f e t y Board's i n v e s t i g a t i o n of a r e c e n tf a t a l a c c i d e n t i n v o l v i n g a Beechcraft Model 18, N310WA, i n d i c a t e s t h a t af a t i g u e f a i l u r e occurred i n t h e e l l i p t i c a l lower cap of t h e r i g h t wingspara t wing s t a t i o n 81. The acci.dent occurred on A p r i l 19, 1973, when t h ea i r c r a f t crashed d u r i n g an approach t o l a n d a t t h e Davenport, Iowa, a i r p o r t .All of t h e s i x people aboard t h e a i r c r a f t were k i l l e d .This i s a n o t h e r i n a long s e r i e s of a c c i d e n t s , d a t i n g back t o 1947,t h a t have been caused by f a t i g u e f r a c t u r e s i n Beechcraft Model 18 wingspars.The Board's staff of i n v e s t i g a t o r s and m e t a l l u r g i s t s have worked c l o s e l yw i t h F e d e r a l Aviation Administration p e r s o n n e l f o r a c o n s i d e r a b l e numberof y e a r s on t h i s problem. One of our i n v e s t i g a t o r s i s c u r r e n t l y workingw i t h t h e FAA and Beech p e r s o n n e l a t t h e Beech f a c t o r y i n Wichita, Kansas,where m e t a l l u r g i c a l and X-ray p l a t e examinations a r e b e i n g conducted.We wish t o commend t h e FAA for t h e i r continued e f f o r t s t o i n s u r e t h ea i r w o r t h i n e s s of Beech 18 a i r c r a f t . We b e l i e v e t h a t your e f f o r t s , whicha r e r e f l e c t e d by t h e numerous AD'S p u b l i s h e d on t h i s problem, have preventedmany a c c i d e n t s . The l a t e s t Airworthiness D i r e c t i v e (72-20-5, Beech) r e q u i r e sa v i s u a l , X-ray, and e i t h e r a magnetic p a r t i c l e o r dye p e n e t r a n t i n s p e c t i o nof t h e lower s p a r caps a t numerous wing s t a t i o n s . We have examined s e v e r a ls e t s of X-rays t a k e n on N310WA i n accordance w i t h t h i s AD. Reexaminationof t h e s e X-ray p l a t e s a t t h e Beech f a c t o r y has d i s c l o s e d t h a t t h e r e wered e t e c t a b l e c r a c k i n d i c a t i o n s i n t h e u l t i m a t e f a i l u r e a r e a d a t i n g back t oJuly 7 , 1971.

- 10 -Honorable Alexander P. Butterfield-2-In view of the above, the Board urges the FAA to examine therecommendation for increased emphasis on the training and qualificationsof radiograph interpreters which was made in the Board's report on the1968 Wein Consolidated F27B accident at Pedro Bay, Alaska, with a viewtoward ultimate FAA certification and licensing of nondestructive inspection technicians.The Board believes, however, that the continuing catastrophic wingfailure accidents and the present state of the art in nondestructiveinspection make it unwise to continue to rely on the quality of presentlyrequired inspections to assure the airworthiness of these aircraft.Therefore, the Board recommends that the Federal Aviation Administration:1. Revise its existing system of surveillance and qualitycontrol of all inspections made under AD 72-20-5to insurethe continued airworthiness of these aircraft.2. Consider a requirement for the incorporation of one ofseveral approved and available kits to reinforce thewingspars on all Beech Model 18 aircraft, which wouldexempt them from further inspection, if the FAA is unableto implement effectively Recommendation No. 1.3. Promulgate an advance Notice of Proposed Rule Makingsoliciting industry views on the practicability oflicensing aircraft radiographic technicians.These recommendations will be released to the public on the issuedate shown above. No public dissemination of the contents of this documentshould be made prior to that date.Reed, Chairman; McAdanls, Thayer, Burgess, and Haley, Members, concurredin the above recommendations.B7Y17

DEPARTMENTOF TRANSPORTATION- 11 -FEDERAL AVIATION ADMINISTRATIONWASHINGTON. DX.MSWMAY 2 5 1973Honorable John 8. ReedC h a i r n u , N a t i o n a l T r a n s p o r t a t i o n S a f e t y BoardDepartment of T r a n s p o r t a t i o n20591Washington, D. C.DearMr. Chairman:This i s i n response t o S a f e t y Recoomendations A-73-16 t h r u -18which a r e concerned w i t h f a t i g u e f r a c t u r e s i n t h e Beech Hodel 18wing.-Safety Recommendation No. 1 Revise i t s (FAA's) e x i s t i n g system o fs u r v e i l l a n c e and q u a l i t y c o n t r o l of a l l i n s p e c t i o n s made underAD 72- 20- 5 t o i n s u r e t h e continued a i r w o r t h i n e s s o f t h e s e a i r c r a f t .-FAA CommentAn a i r m a i l a i r w o r t h i n e s s d i r e c t i v e amendment t oAD 72- 20- 5 waa issued A p r i l 23, 1973. Paragraph D ( 2 ) r e q u i r e s t h a tthe two most r e c e n t c o p i e s of X-rays t a k e n i n accordance w i t hAD 72- 20- 5 or p r e d e c e s s o r A D S be t r a n s m i t t e d t o the F e d e r a l A v i a t i o nAdministration, Engineering and Manufacturing Branch, Wichita,Kansas. where e v a l u a t i o n of t h e i n s p e c t i o n f a c i l i t i e s ' f i n d i n g s w i l lbe made. A l l domestic r e g i o n s have been n o t i f i e d v i a telephone t oput more emphasis on Beech 18 a i r t a x i o p e r a t o r maintenance,p a r t i c u l a r l y i n compliance w i t h AD 72- 20- 5 and t h e a i r m a i l amendment.-Consider a requirement f o r the incorSafety Recommendation No. 2p o r a t i o n of one of s e v e r a l approved and a v a i l a b l e k i t s t o r e i n f o r c ethe wingspars on all Beech Model 18 a i r c r a f t , which would exemptthem from f u r t h e r i n s p e c t i o n , i f the FAA i s unable t o implemente f f e c t i v e l y Recoomendation No. 1.-FAA CommentAmended AD 72- 20- 5 r e q u i r e s w i t h i n 600 h o u r s t h a t wings t a t i o n s 7 3 and 81 be modified i n accordance w i t h Beech k i t s 18- 4024and 7 9 1 , and w i t h i n 2000 hours, b u t not l a t e r than May 1, 1975, t h a twing s t a t i o n s 3 2 , 57 and 64 be modified i n accordance w i t h Beech k i t s18- 4024 and 7 9 1 o r an approved e q u i v a l e n t .

- 12 2-Safety Recomnendation No. 3P r m l g a t e an advance Notice of ProposedRule Making s o l i c i t i n g industry views on the practicability o f l4censinga i r c r a f t radiographic technicians.-FAA ComentWe are studying t h i s recormnendation and we w i l l advise youof our decision.Sincerely,

-13-BEECHsednsing3youAPPENDIX DAirworthiness DirectiveRevisionVolume I72-20-5 Beech. Amdt. 39-1526 as amended byAmendment 39-1832. Applies to all serialnumbers of Models C18S, AT-11, C-45,C45A, UC-45B, UC-45F, AT-7, AT-7A,AT-7B, AT-i’C, JRB-1, JRB-2, JRB-3, JRB-4,SKB-1, SNB-2, SNB9C, D18S, D18C,C-4SG, TC-45G, C-45H, TC-45H, TC-4SJ(SNB-5), JRB-6, E18S, E18S-9700, G18S,3N, 3NM, 3TM, D18C-T, and RC-45J(SNB-5P), and H-18 airplanes with SerialNumbers BA-730 and hclom; and to aircraft of the above models subsequentlyredesiqnated under a Supplemental TypeCertificate, except those modified under the Supplemental Type Certificates referenced by Paragraph F.Compliance: Required as indicated, unless already accomplished.To prevent possible wing failure, for airplanes with 1,500 or more total hours’ timein service on the effective date of this ADor airplanes that subsequently accumulate1,500 total hours’ time in’ service after thatdate, in order to detect cracks in the elliptical front spar lower cap of the wing cen-ter section, except as indicated by Paragraph D, accomplish the following withinthe next 50 hours’ time in service after theeffective date of this AD (or 500 hours’time in service after the last complete AD67-16-I/ 71-11-5 or AD 72-85 inspection,applicable), and thereafter at intervals notto exceed 500 hours’ time in service fromthe date of the date of the last inspection:(These inspections may be performed atone time or may be staggered, provided thatno given area exceeds 500 hours’ time inservice between inspections.)‘ i fA ) Modify the lower wing skin in accordance with Figure (1) or Figure ( 2 ) or anFAA-approved equivalent to facilitate theinspections specified in Paragraph B.B. (1) Inspect the front spar lower capof the wing center section on each side ofthe airplane by methods specified below,except inspection sites reinforced by BeechAircraft Corporation Kits 18-4024, 791 or792 need not be inspected:Site (See Figure 3)Method (See Para. C)-90Tips of welds at clevis tangs, upperand lower surfaces of capVisual, x-ray and either magneticpart‘icle or penetrant81, 73, fJ4 & 57Tips of welds at gussets, upper surface of cap48Outboard ends of splice in cap, upper and lower surface of cap32Tips of welds at wing splice plate,fore and aft surfaces of cap45 to 43Tip of weld around cluster uppersurface of cap61Lower surface of spar cap belowtube cluster, as seen from wheel wellWing Station,,nN,,I,0N,,,,Visual and either magnetic particle or penetrantI,,,,

- 14 -2( 2 ) Temporarily move clamps andother equipnwnt as nc.cvssary to eliminateinterference with the ahwe inspections. Removal of spar cap finish is not necessary.( 3 ) Flex the wing whrn specified b yParagraphs C and D hy applvill!: and relieving a 75 to 100 porlntl rlpward force ator near the wing tip on the (left or right)side being inspected. Thib may he done byhand.( 4 ) Load the wingthc side hringinspected when specifid h y Pnragrapl; Cby applying a 7,5 to 1 0 0 po11nc1 upwardforce at the jnnctiort o f \r.inx rib 1uImbcr I 0and the front spar. Placr matrrial snch aslumber under and along the nnmh(*r 10 ribso as to distrihute the force.(111C. i1 ) Accomplish visual inspection hvforo and after cleaning. and w h i k thr wingis being flexed. Use a flashlizht o r otherillrlmination and a low power mtlguifyingdevice.(2) When the majinetic particle method is chosen, conrlnct the inspection whilc.the wing is either flexed or IoaJetl. Conduct the inspection before magnetim isindneed and again while magnetisn acrossthe inspection site is inchwed by a hlagnaflux Corp Model Y-S or Y\I-5 yokt: or whenany equivalent is wed ill accordance withthe manufacturer’s instructions.( 3 ) When the penetwnt mrthod ischosen. perform the inspcction while thewing i y bcing flexed. Use either dye orflnorescmt materials in accordance with theperwtrant manufacturer’s instructions.( 4 ) For each site \vhere x-ray inspection is specified by Paragraph B, accomplish x-ray inspection while the wing isloaded. Figure 4 is an aid to the followinginstruction. Place fine grain film (such asGAF 800, Dnl’ont NDT-6.5 or Kodak A A )sandwiched between lead screens of 0.005inch thickness on the upper surface of thespar cap (over an inspection site) with identification symhols for at least the site (e.g.LWS 81 etc.), date, and airplanr registration number. Secure a steel prnetrameterof 0.005-inch thickness to the lower surfaceof the spar cap at a location clear of theinspection ,site. Position the x-ray sourceapproximately 36 inches from and generallybelow the film so that the center of thex-ray beam will be perpendicular to themajor axis of the elliptical spar cap andperpendicular to the spanwisr centerline ofthe spar cap at each inspection site. Use aflashlight and a protractor level as necessaryto see that aiming of the x-ray beam conipensates for wing dihedral and nose upattitude. At those areas covered by aluminum skin, a locally fabricated jig maybe used to position the x-ray snnrce. Exposefilm so that density of the radiograph ofthe spar cap material near the inspectionsite is 1.5 to 2.8 on the densitometer orNational Burean of Standards density scale.View film to see that the inspection site,the 0.010 inch diameter hole in the penetrameter, and its entire outline are plainlyshown. Using a low power magnifying device, examine the inspection site portion ofeach radiograph for faint indications ofcracks in spar cap material transverse to thespanwise centerline.NOTE: Fourteen radiographs are normally adequate for one complete inspection.D ) 1. A special inspection at wing station 73 and 81 is required within 25 hours’time in service after the effectivr date ofthis amendment regardless of prrvions timein service since last insprcti( nand thrre/after at intervals not to exccrd 100 hours’time in service. Visual and cither magneticparticle or penetrant methods mnst be usedwhile the wing is simultaneously flexed.( 2 ) Within 48 hours after the effectivedate of this amendment, transmit h y mostrapid means copies of X-rays of the two[most recent inspections taken in accordancewith AD 72-20-5 or predecessor ADS toDOT/FAA. Engineering and ManufacturingBranch, Hangar #lo, Wichita Municipal Airport, Wichita, Kansas 67209. Evaluationof inspection facility’s findings will be transmitted to sender as soan as possihle.3 ) Withinhours’ time in service11 after (theeffective date of this amendment,,,600na1tIat\.!4tI1i11

r- 15 clear of thex-ray sourcend generallyw e r of the:ular to thebar cap and“enterlin

This report contains Aviation Safety Recommendations A-73-16 through A-73-18. 6.Abstract Air Iowa, Inc., Flight 333, a Beech Aircraft Model E18S, N310WA, scheduled as an air taxi passenger flight, crashed into an open field about 1704 c.s. ., on April 19, 1973, while approachi