LAX95LA067 · Harris BD-10

THE FLIGHT'S TEST CARD CONCERNED EXPANSION OF THE SPEED ENVELOPE FROM 370 TO 380 KIAS. ON AN EARLIER TEST FLIGHT AT 350 KIAS, THE SIDE LOAD FORCES ON THE VERTICAL STABILIZERS REACHED A COMPANY IMPOSED LIMIT OF 40 PERCENT OF THE ULTIMATE FAILURE LOAD DETERMINED BY THE DESIGNER. DURING THE RUN BETWEEN 375 AND 380 KNOTS, THE AIRCRAFT PITCHED VIOLENTLY NOSE UP FOLLOWED BY A GENERAL BREAKUP. THE COMPANY SAID THE ORIGINAL BEDE BUILT BD-10 PROTOTYPE SUSTAINED A VERTICAL STABILIZER FAILURE DURING FLIGHTS AT THE 1994 RENO AIR RACES. BEDE SUBSEQUENTLY DESIGNED A FIX WHICH STRENGTHENED THE VERTICAL TAILS. GROUND SUBSTANTIATION LOAD TESTS TO FAILURE WERE CONDUCTED BY BEDE, AND THE RESULTING YIELD FAILURE LOAD LIMIT WAS PROVIDED TO THE COMPANY, WHICH USED THE NUMBERS TO ESTABLISH THE 40 PERCENT FLIGHT TEST LIMIT. THE NEW FIX WAS INCORPORATED INTO THE ACCIDENT AIRCRAFT. WRECKAGE EXAMINATION REVEALED THAT THE AIRPLANE'S VERTICAL TAILS SUSTAINED STRUCTURAL OVERLOADS AND SEPARATED FROM THE AIRCRAFT IN FLIGHT. THE INTACT LEFT VERTICAL TAIL ASSEMBLY WAS FOUND EARLY IN THE WRECKAGE PATH AND EXHIBITED A CLEAN, ALMOST INSTANTANEOUS FAILURE LOAD WITH RIGHT BENDING AT THE SPAR TO FUSELAGE ATTACH POINTS. A PRODUCTION CONFIGURATION LEFT SIDE EMPENNAGE WAS BUILT, PUT IN A TEST FIXTURE, AND THE VERTICAL TAIL LOADED TO FAILURE. THE FAILURE MODE AND SEPARATION POINT WAS THE SAME AS THAT SEEN ON THE ACCIDENT AIRCRAFT LEFT VERTICAL TAIL ASSEMBLY. THE VERTICAL STABILIZER SPARS BEGAN TO YIELD AT 40 PERCENT OF THE FAILURE LOAD LIMIT SUPPLIED BY BEDE. SPAR FAILURE OCCURRED AT 65 PERCENT.

Verbatim NTSB analysis and probable cause from the NTSB dataset