The arrival of the jet age promised faster journeys, greater passenger comfort, and a new era of commercial aviation, but it also presented aircraft manufacturers with an important engineering challenge: building a pressurized fuselage that could withstand thousands of flights without suffering a catastrophic structural failure. For Boeing, developing the 707 meant proving that a large aircraft could safely endure the repeated stresses of climbing to cruising altitude and descending to the ground, even when its metal skin suffered damage.