[Learjet 23 fuselage undergoing testing in hydrostatic tank]

Photograph of people observing a Learjet 23 fuselage undergoing testing in a hydrostatic tank, January 15, 1964. William P. Lear (in vest) is on the left.

Typed caption on verso: "Meets FAA requirements: / Both fail-safe and ultimate fatigue tests were witnessed last week by President Bill Lear (left foreground in vest), test engineers and FAA personnel. / Number Two airframe successfully withstood 20,000 pressurization cycles in the hydrostatic tank at zero to 8.8 lbs. per-square-inch, as well as an ultimate load of 18.2 psi. / The rapid cycling period of 27.5 seconds (from 0 to 8.8 and then back to 0 psi pressure) is believed to be an industry record. / Portions of the cabin fuselage structure and windshield were then intentionally weakened for fail-safe testing. Recycling from zero to 8.8 psi was resumed to demonstrate that crack propagation would be limited to a non-catastrophic extent. / The large, perfect-view windshield -- which had been deliberately sliced in two different places and at opposite angles -- was found fail-safe because of redundant load paths throughout, plus proven crack-stopper techniques along with dual windshield and window panes -- each capable of withstanding full cabin pressure of 8.8 psi. / The yard-wide door on the cabin's port (left) side was also subjected to ultimate pressurization load of 18.2 psi. / This clam-shell door's fail-safe characteristics were further demonstrated by removing fastening pins, one at a time, to prove it could satisfactorily undergo 8.8 operating pressure without failure. (Lear Jet - 15 January 1964)."