High-flying aircraft that are approaching you "streak upwards"; those that are receding from you "dive downwards". Things come up over the horizon, and they go down below it, even if they are traveling along horizontally.
The "streak" in TWA800 was from the fire initiated by the initial blast in the center tank. It connected to a "fireball" from the bulk of the rest of the fuel burning.
For a fine example of journalistic integrity and inquisitiveness, after a slow start, and some associated conspiracist buffoonery, google "LA missile launch catalina helicopter".
Mystery Missile Launch Seen off Calif. Coast - CBS News