Flipside Movie Emporium

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Hello all...

I am suffering from the latent memory of what I believe is a made-for-TV movie from the 1970's. I was just a kid when I saw it, but it has left an indelible impression on me. So far I have been unsuccessful in turning up the title, and I'm hoping someone can help.

To the best of my recollection, the movie opens with a shot of an unattended ham radio sitting on a desktop. Over the radio we hear the final moments of a hijacked passenger airliner as it crashes into the ocean, the victim of a failed heist. The hijackers were attempting to steal something in the plane's cargo hold--gold, I think. (Or perhaps the crash was an intentional part of the plan...I don't remember.)

Years(?) later, the movie's main character is tapped to pilot a small submarine, which is being used by the bad guys behind the original plot, to locate the sunken plane and retrieve the loot. What they do not know is that their submarine pilot lost his wife (and possibly a child?) on that plane, and has infiltrated their organization to identify the men responsible and obtain the evidence he needs to bring them to justice.

In the movie's climax, our hero takes two of the bad guys down to the sunken plane. In the sub's floodlights the gold is illuminated, along with the skeletal remains of some of the crash victims. Suddenly he cuts power to the sub, allowing it to come to a rest on the ocean floor. After disabling the sub's air supply, he reveals all to the thieves, who threaten to kill him; he points out that he is the only one who can operate the sub--if they kill him, they will die as well. As the available air in the sub dissipates, all three men begin to suffocate. Just before collapsing, one of the panicking thieves confesses on tape. Our hero nearly blacks out before finally restoring the air supply. Falling to the vent near the floor, he gulps in the fresh air.

This is the only movie in my experience that has ever defied identification for so long. I can find nothing on Amazon, the IMDB (Internet Movie Database), through general internet searches, or anywhere else. The Incredible Inman has even failed to respond to my inquiries. Any information which would clue me in to this movie's title would be greatly appreciated.

Thanks in advance!