Spar Web brief 09/05

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Spar Web brief 09/05 1 ADs 90-08-04 / 95-04-03 MSBs 53-2269 / 2360 Carry-Thru Spar Web Cracks American Bonanza Society/ ABS Air Safety Foundation Spar Web brief 09/05 2 Mandatory Service Bulletins • MSB 2269 issued August 1989 – Barons (except 58P and 58TC) – Travel Airs • MSB 2360 issued November 1990 – Bonanzas H35 and later – All Model 33 Debonairs/Bonanzas – All Model 36 Bonanzas Spar Web brief 09/05 3 Airworthiness Directives • AD 90-08-14 – Incorporates MSB 2269 (multiengine) • AD 95-04-03 – Incorporates MSB 2360 (singe engine) To date there have been NO reports of aircraft mishap or in-flight failure resulting from cracks in wing carry- through spar web structure. Spar Web brief 09/05 4 Carry-through spars Spar Web brief 09/05 5 Spar Web brief 09/05 6 Tie Plates • Carry loads between ends of carry-thru in Huck bolt area • Potential damage to tie plates and internal C-channels make stop drilling hazardous in this area • ABS’ contract engineers feel there are techniques to get around this problem Spar Web brief 09/05 7 Tie Plates • Tie plates may carry the load • Lower material may not carry carry-thru loads • Tie plates differ in different models • Need to further investigate the design Spar Web brief 09/05 8 Current AD Inspection • Initial inspection @1500TT • No cracks: every 500 hours thereafter Spar Web brief 09/05 9 Current AD Inspection (continued) If cracks in web near/through huck bolts: • <1.0 inch: – reinspect at annual/every 200 hours • >1.0 inch or connecting two huck bolt holes or cracks on forward and aft side of web on same side of aircraft: – Install Beech doubler repair kit Cannot stop drill through web: damage beneath Spar Web brief 09/05 10 Current AD Inspection (continued) Cracks in the flange radius: • <2.25 inch: – Stop drill crack – Reinspect every 200 hours thereafter • 2.25 – 4.0 inch – Install Beech doubler repair kit within 100 hours • >4.0 inch – Install Beech doubler repair kit prior to flight Spar Web brief 09/05 11 Doubler Installation Spar Web brief 09/05 12 RAC Communiqué 103 Issued October 2003: • “The FAA no longer allows aircraft operation with known cracks….” • RAC “is in the process of revising both service bulletins to remove any reference to continued flight with cracks in the spar web. The revised service bulletins…will require repair of any crack found during inspection of the spar web regardless of size." Spar Web brief 09/05 13 MSB Revisions June 2004 • “At the request of the FAA….” • Eliminates option of continued flight with identified spar web cracks (and accelerated inspections) • Not “mandatory,” but may be required under Part 135 and for some foreign- registered airplanes ABS Comparison sheet Spar Web brief 09/05 14 ABS Investigation • Initial contact with FAA and RAC to confirm moving toward “no cracks” in “primary load-bearing structure” • January 2004: Dick Wilson calls ABS with opposing view • Engineering study grew from an independent “peer review” of Wilson Spar Web brief 09/05 15 Engineering Reports Probable cause of spar web cracking • Low-intensity, frequently repeated loads from normal operation • Primarily driven by nose gear loads during landing and ground handling • Longitudinal stresses directed around the fuselage skin wing spar cutouts Spar Web brief 09/05 16 Spar Web brief 09/05 17 J Stringer Spar Web brief 09/05 18 Spar Web brief 09/05 19 Spar Web brief 09/05 20 Spar Web brief 09/05 21 Spar Web brief 09/05 22 Engineering Reports (continued) Probable cause of spar web cracking • Initial Huck bolt-area cracks allow flexing that develops to bend radius cracks • The engineers “doubt the validity” of Wilson’s work and “cannot agree with his conclusion that the cracking will not potentially cause safety problems.” Spar Web brief 09/05 23 Engineering Reports (continued) Current MSB effectiveness • Kit repairs cracks locally but does “very little for the fore and aft loads that are the cause of cracks seen to date.” • Kit increases stiffness and therefore increases web stresses • Kit in conjunction with “a robust external doubler to the fuselage skin should cause no harm.” Spar Web brief 09/05 24 Engineering Reports (continued) Engineers’ recommendations • It is vital to obtain all available information • A Finite Element Analysis is “essential to…validate any proposed repair….” Spar Web brief 09/05 25 Other ABS Actions • Regular FAA and Raytheon contacts • Airworthiness Concern Sheet, September 2004 • AOPA meeting November 4, 2004 • GAMI meeting November 8, 2004 • National Institute for Aviation Research • T-34, Twin Cessna, Twin Beech, T-6 issues Spar Web brief 09/05 26 ABS Member Survey • 1770 responses – 32% of ABS members with affected airplanes – estimated ~14% of remaining affected fleet • 110 aircraft (5.9%) MSB-defined crack • 52 aircraft (2.9%) require doubler under existing rules • 60 aircraft (3.3%) cracked but do not currently require doubler Spar Web brief 09/05 27 ABS Member Survey (continued) H35 – K35 0 reports M35 – P35 1 report S35 – V35B 15 reports 33 (IO-470) 4 reports 33A/C 7 reports 36 32 reports Spar Web brief 09/05 28 ABS Member Survey (continued) Travel Air 1 report 55/56TC 29 reports 58 14 reports Spar Web brief 09/05 29 ABS Member Survey (continued) • Best information is that this limited response is indicative of fleet as a whole • Still does not account for RAC’s report it has sold 2000 spar repair kits • Post-AD airplanes • Information on cracks that have propagated into upper web Spar Web brief 09/05 30 ABS Position Given that: • Beechcraft spar web cracking has been a “known problem” for well over a decade; • In that time there has been no aircraft failure or mishap attributed to spar web cracking; • Current AD procedures have prevented mishaps Spar Web brief 09/05 31 ABS Position (continued) ABS therefore requests that: • Current Airworthiness Directive procedures should not be revised until such time as additional, detailed analysis