panels on their screens. you can see what they are doing with their hands. >> reporter: cameras on the instruments wouldn't necessarily give investigators much help in the germanwings crash probe. they already know how that plane went down technically. but former commercial pilot lynn spencer says cameras trained on pilots' faces could catch certain moments that cockpit voice and flight data recorders might miss. >> was the pilot choking. is the pilot having a seizure. >> reporter: the technology's already on the market. but one manufacturer told us no airlines have bought their cameras. cameras are already used to monitor key missions like today's launch to the international space station. they are used to watch some train operators, taxi drivers, and bus drivers, including this one, caught looking at his phone, then crashing. cockpit video could even be live streamed back to controllers on the ground in realtime although the expense of installing and streaming thousands of live cameras could be prohibitive. spencer says cockpit cameras could have provided key evidence in some of the most infamous