tank using small removable inspection hatches in the top surface of the wing. This resulted in poor visibility and awkward conditions for working inside the tank. The sealant concealed the previous repair to the stringer and made subsequent checking for further damage to this component (i.e., any crack growth) impossible. The first outward sign of possible significant problems with the accident aircraft was when a chord-wise (running from the front of the wing towards the rear) crack was noticed in the skin of the lower surface of the right wing at the root. After several failed attempts at stopping the crack by drilling stop-holes, the crack was repeatedly repaired by affixing doublers (metal patches intended to take over the load from the damaged part, a normal repair procedure for minor skin damage), which were riveted over the cracked skin. However, the crack continued to grow, requiring longer and longer doublers to be fitted. Although the skin crack was slowly getting longer it was not thought to be anything other than a skin problem, which could be dealt with by affixing a doubler. Like most aircraft of the period, the Mallard was built using an aluminium stressed skin construction. Unlike earlier fabric covered aircraft where the fabric covering is merely for aerodynamic purposes and contributes little to the overall strength of the airframe, the metal skin itself carries part of the flight loads and is stressed during flight. Many such aircraft develop minor skin cracks over time; provided appropriate action is taken to repair any cracking, the safety of the aircraft is not compromised. The unseen cracked stringer on the accident aircraft allowed the right wing to flex more during flight which increased the bending forces at the root such that the visible skin crack slowly increased in length with each subsequent flight. The crack in the underside of the wing grew in length until the wing was so weakened it was unable to support the flight loads during the accident flight, and the wing separated. This caused the fuel contained within the wing to be released and ignite, resulting in the fire seen by witnesses. By sheer chance, a tourist from New York was able to videocapture Flight 101's final moments on his cell phone as the plane went plunging down towards the ocean. The footage clearly showed the airplane and the right burning wing falling on two separate spots