This problem resulted in the breakup of three early 1950’s aircraft under then mysterious conditions. Investigations revealed that the cause was __________ ___________, from the flexing of the structure caused by pressurization /depressurization cycles.7. Wrinkles observed during the preflight inspections in the top of the wing or the bottom of thehorizontal stabilizer and / stretch marks on the bottom of the wing or top of the stabilizer that weren’t there during the manufacturing process are good evidence of _______________ ____________, due to overstressed flight and the aircraft is no longer airworthy.8. One process to prevent aluminum alloyed metal corrosion is by _____________. This involvescovering the aluminum allow metal with pure aluminum, thin coating, rolled onto the surface.