The diffuser cracks reduced support for the No. 3 and No. 4 bearings, caus- ing misalignment of the power turbine shaft, rubbing on the blade shrouds, and ultimately an imbalance of the power turbine rotor assembly. This in turn caused additional cracking in the exhaust diffuser and rubbing with the rear compressor stub shaft. Frictional heating of the stub shaft caused the failure of the No. 2 bearing, bringing the engine to a stop. The evidence that damage to the
exhaust diffuser likely preceded the accident raised the question of why it hadn’t been detected in previous inspections—a key point in the NTSB’s exploration of the multiple and poten- tially ambiguous regulations governing restricted and experimental exhibition category aircraft and the operation of “living history” flights.
The Regulations The foundational requirements for inspection and maintenance of US-registered civilian aircraft are, of course, contained in Title 14 of the Code of Federal Regulations (CFR). Part 43.15(c)(1) of Title 14 requires that “each person performing an annual or 100-hour inspection shall use a checklist” but allows that “the checklist may be of the person’s own design”—necessary in the case of both experimental amateur-built aircraft and orphaned historic models for which no manufacturer’s checklists are known to exist. Appendix D to Part 43 outlines a generic inspection checklist, listing types of components to be examined in each “group” of aircraft structures (“cockpit and cabin,” “engine and nacelles,” etc.). In the case of the Bell UH-1 series,
however, model-specific proce- dures were indeed published in US Army technical manuals (TMs)—TM
55-1520-219-10, issued in January 1969, and TM 55-1520-219-20, dated Jun. 30, 1972. The operating limita- tions attached to N98F’s initial special airworthiness certificates in both the restricted and experimental exhibition
categories specifically required that the aircraft “must be operated and maintained” in accordance with those references. Additional army manuals provided checklists for daily, intermediate,
FIGHTING FIRES WITH
STRENGTH & RELIABILITY
AROUND THE GLOBE
BAMBIBUCKET.COM
DEC 2024 POWER UP
61
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76
