Aircraft Accident Report I

I N A T I 0 N AIRCRAFT ACCIDENT REPORT A I L AIR IOWA, tNCORPORATED T BEECH EM; N310WA R A DAV.ENPORJ, IOWA N APRIL 19, 1973 I S P 0 R T A T I 0 N S A F E T Y B - FILE NO. 3-1558 AIRCRAFT ACCIDENT REPORT AIR IOWA, INCORPORATED BEECH E18S, N310WA DAVENPORT, IOWA APRIL 19, 1973 ADOPTED: OCTOBER 3, 1973 NATIONAL TRANSPORTATION SAFETY BOARD Washington, D.C. 20591 REPORT NUMBER: NTSB-AAR=73-18 TECHNICAL REPORT STANDARD TITLE PAGE . Report No. 2.Government Accession No. 3.Recipient's Catalog No. VTSB-MA-73-18 . Title and Subtitle Aircraft Accident Report - 5.Report Date AIR IOWA, INC., BEECH E18S, N310WA October 3, 1973 DAVENPORT, IOWA " 6.Performing Organization APRIL 19. 1973 Code . Author(s) 8.Performing Organization Report No. Performing Organization Name and Address 10.Work Unit No. 1084-A National Transportation Safety Board 11 Bureau of Aviation Safety .Contract or Grant No. Washington, D. C. 20591 13.Tvpe of Report and Period Covered 2.Sponsoring Agency Name and Address Aircraft Accident Report April 19, 1973 NATIONAL TRANSPORTATION SAFETY BOARD Washington, D. C. 20591 14.Sponsoring Agency Code I 5.Supplementary Notes 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 approaching the Municipal Airport, Davenport, Iowa, for a landing. The pilot and five passengers were fatally injured. There were no injuries to persons on the ground. The aircraft was destroyed by impact. The National Transportation Safety Board determines that the probable cause of this accident was the in-flight failure of the right wing,which resulted from a preexisting fatigue crack in the lower spar cap of the wing at Wing Station 81. Although the fatigue crack existed and was discernible during inspections conductf over the 6-year period prior to this accident, it was,not detected. 17.Key Words 18.Distribution Statement This document is available Wing spar failure in flight to the public through the Airframe failure in flight National Technical Fatigue crack Information Service, Inadequate inspection Springfield, Virginia 22151 19.Security Classification 20.Security Classification 21.No. of Pages 22.Price (of this report) (of this page) UNCLASSIFIED UNCLASSIFIED 20 NTSB Form 1765.2 (11/70) ii AIR IOWA, INCORPORATED BEECH E18S, N318WA DAVENPORT, IOWA APRIL 19, 1973 TABLE OF CONTENTS Page Synopsis . 1 Investigation . 2 Analysis and Conclusions . 4 Probable Cause . 5 Recommendations . 5 Appendices Appendix A - Crew Information . 7 Appendix B - Aircraft Information . 8 Appendix C - Safety Recommendations A-73-16 through 18 . 9 Appendix D - Airworthiness Directive 72-20-5 .. 13 File No. 3-1558 NATIONAL TRANSPORTATION SAFETY BOARD WASHINGTON, D. C. 20591 AIRCRAFT ACCIDENT REPORT Adopted: October 3, 1973 AIR IOWA, INCORPORATED BEECH E18S, N310WA DAVENPORT, IOWA APRIL 19, 1973 SYNOPSIS Air Iowa, Inc., Flight 333, a Beech Aircraft Model E18S, operating as a scheduled air taxi passenger flight, crashed into an open, plowed field about 1704 central standard time, April 19, 1973, while approaching the Municipal Airport at Davenport, Iowa, for a landing. The accident occurred approximately 3 miles southwest of the Davenport Airport. The pilot and five passengers were fatally injured. There were no injuries to persons on the ground. The aircraft was destroyed by impact forces; there was no fire. The National Transportation Safety Board determines that the probable cause of this accident was the in-flight failure of the right wing, which resulted from a preexisting fatigue crack in the lower spar cap of the wing at wing Station 81. Although the fatigue crack existed and was discernible during inspections conducted over the 6-year period prior to this accident, it was not detected. As a result of this accident, the Safety Board made three recormnenda- tions to the Federal Aviation Administration regarding the quality of present inspection methods and the need for reinforcement of the wing structure of Beech Model 18 aircraft. -2- INVESTIGATION On April 19, 1973, a Beech Aircraft, Model E18S, N310WA, was operating as Air Iowa, Inc., Flight 333 ( a scheduled air taxi) from Muscatine, Iowa, to O'Hare International Airport, Chicago, Illinois, with a scheduled en route stop at Davenport, Iowa. The flight departed from the Muscatine Airport about 1650 c.s.~.,L/ on a VFR z/ flight, with no flight plan. There was no record of any radio communication with Flight 333 before its departure from Muscatine or while it was en route to Davenport. Neither the Muscatine Airport nor the Davenport Airport is cmtrolled. The witnesses in the vicinity of the impact area generally agreed that when they first observed the aircraft, it was in level flight, clear of the clouds, and flying at an estimated altitude of 1,500 to 2,000 feet above the ground, with gear and flaps retracted. While the aircraft was approaching the witnesses' position, the right wing suddenly folded upward. As the wing folded, the aircraft rolled to the right and nosed down into an uncontrollable dive to the ground. The witnesses stated that there was no visible fire or smoke or separation of any parts from the aircraft before ground impact. The aircraft struck the ground in a nearly vertical nosedown attitude, and was demolished. The aircraft was fragmented by impact forces. The wreckage, which was strewn along a ground path approximately 170' magnetic, was confined to an area about 210 feet long and 110 feet wide. All major components and extrem- ities of the aircraft were accounted for near the point of initial impact. There was no evidence of in-flight fire or explosion. Examination of both engines showed no evidence of in-flight malfunction or failure. The landing gear and flap assemblies were in the fully retracted position. Damage to the upper outboard right wing attach forging showed that the outboard panel had rotated upward about the hinge fitting approximately 115' before impact. This was confirmed by ground impact marks. The left wing structure was attached and in place at time of impact. On-scene examination of the right wing disclosed a fracture in the tubular lower front main spar cap of the right center section truss assembly at Wing Station (WS) 81. Visual inspection of this separated area showed -1/ All times are central standard, based on the 24-hour clock. -2/ Visual Flight Rules I -3- that approximately 80 percent of the tube wall had failed in fatigue before final separation. ating Metallurgical examination of portions of the left and right wing lower Iowa, spar caps disclosed the following: n route rt 1. The separation of the right wing, lower spar tube at WS 81 resulted from a fatigue crack which originated at the toe of the weld joining the gusset plate to €ore the lower spar tube. The crack progressed trans- either versely in both directions around the spar tube over approximately 80 percent of the tube wall bef0r.e the final failure occurred in tension overload. that E the 2. All other fractures in the center section truss 7e the assembly were typical of fracture caused by overload. ling ! wing As a result of previous service experience, the Beechcraft Model 18 :ollable wing spar structure was the subject of a number of company service bulletins 'e or and of Federal Aviation Administration (FAA) Airworthiness Directives which listed procedures to detect the presence of fatigue cracks. ude , After this accident, Board investigators reviewed the records of seven radiographic inspections, made by various repair stations dating back to 1967, which related to the area in which this fracture occurred, Crack I was indications on a number of X-rays, which were clearly visible to Board an investigators, had not been reported by the inspecting facilities. xtrem- ct. The procedures for detection of cracks in the elliptical front spar cap of the wing center section are outlined in FAA Amendment 39-1526 to Airworthiness Directive 72-20-5, effective September 29, 1972. The radio- c t ion graph exposure of the X-ray film, also specified in this amendment, should racted be from 1.5 to 2.8 on the densitometer of the National Bureau of Standards d density scale. The radiograph exposures of several of the X-ray films oxi- examined were found to be outside the allowable tolerances. The densities The of this film ranged from 0.5 to 5.0. The procedures and densities specified in Amendment 39-1526 were also specified in the amendments issued before September 1972. EdlY All of the required inspections were accomplished within the specified ed flight time limits. The aircraft had been flown approximately 66 hours after the last radiographic and magnetic particle inspection conducted on - March 21, 1973. -4- ANALYSIS AND CONCLUSIONS The outer panel of the right wing failed in flight and rotated upward approximately 115O before the aircraft struck the ground, which confirms the statement of witnesses that the right wing folded upward in flight. Metallurgical examination of the right wing tubular lower spar cap showed that the wing failure was caused by a fatigue fracture in the lower spar at Right WS 81. This was the fifth fatal accident since June 1964 that involved wing failure in Beechcraft Model 18 aircraft resulting from a fatigue fracture at WS 81. All of these wing failures occurred in areas where inspections designed to detect fatigue cracks were required by Airworthiness Directives. Again, the problems in detecting fatigue cracks during these required inspections are clearly demonstrated in this accident.

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