News reports say that a Cathay Airlines flight crew on November 29 reported seeing North Korea’s missile “blow up and fall apart” during its recent flight test. Since reports also refer to this as happening during “reentry,” they have suggested problems with North Korea’s reentry technology.
But the details suggest the crew instead saw the missile early in flight, and probably did not see an explosion.
One report of the sighting by the Cathay CX893 crew gives the time as about 2:18 am Hong Kong time, which is 3:18 am Japan time (18:18 UTC). According to the Pentagon, the launch occurred at 3:17 am Japanese time (18:17 UTC), which would put the Cathay sighting shortly after the launch of the missile from a location near Pyongyang, North Korea.
Since the missile flew for more than 50 minutes, it would not have reentered until after 4 am Japanese time. Given the timing, it seems likely the crew might have seen the first stage burn out and separate from the rest of the missile. This would have happened a few minutes after launch, so is roughly consistent with the 3:18 time.
The New York Times posted a map that shows the track of flight CX893. It shows that the flight was over northern Japan at 6:18 pm UTC (Fig. 1) and the pilots would have had a good view of the launch. By the time reentry occurred around 7:11 pm UTC, the plane would have been over mid-Japan and reentry would have occurred somewhat behind them (Fig. 1).
Burnout of the first stage would have taken place at an altitude about 100 km higher than the plane, but at a lateral distance of some 1,600 km from the plane. As a result, it would have only been about 4 degrees above horizontal to their view—so it would not have appeared particularly high to them. Ignition of the second stage rocket engine and separation of the first stage may have looked like an explosion that caused the missile to fall apart.
There are also reports of two Korean pilots apparently seeing a “flash” about an hour after the missile’s launch, which would be consistent with the warhead heating up during reentry, since the missile flew for 53-54 minutes. Neither reported seeing an explosion, according to the stories.