Cockpit Sliding Windows -- visibility, ventilation
This may not be obvious: the biggest risk of inflight fire is eventual Loss of Control.
Fatal fire and crash, TWA Lockheed Constellation NC86513 Star of Lisbon, ... near Reading, PA 11Jul46. Sixteen minutes after T/O (during practice engine-out ops) an F/E smelled odor of burning insulation; when he opened cockpit-bulkhead Door to cabin blast of heat and dense black smoke poured into cockpit. Smoke in cockpit inhibited pilots Nilsen and Brown from seeing panel. Cockpit crew-hatch was opened to clear air, but this only drew more smoke into cockpit. IP Brown opened right sliding window; Brown put head out window and flew aircraft to emergency landing (smoke created danger of losing control). Landed 2 miles NE of airport, skidded 1000' across hay field. Tanks ruptured, fuel fire. Only IP-PIC RF Brown survived (burned, amputee) ...
Varig 820 / 11Jul73,
Clipper 160 / 3Nov73,
Air Canada 797 / 2Jun83
In the Varig, Pan Am, and Air Canada cases, and in others, the smoke accumulation in the cockpit became so thick (and physically irritating) as to motivate pilots to open their cockpit Sliding Window. In the case of UA 823 / 9Jul64 the smoke/fire in the cabin motivated a passenger to open the Over-wing Exit while still in flight.