It may be descending because it's lost its gas or maybe deliberately because it's done its duty and now committing suicide. If, before, it was flying as low as 19,000 ft. they might have had to file a flight plan because it would have been in commercial airspace. For a spy device? Not likely. It's more likely that it WAS flying much higher and now is descending and at a lower altitude.
It may be descending because it's lost its gas or maybe deliberately because it's done its duty and now committing suicide. If, before, it was flying as low as 19,000 ft. they might have had to file a flight plan because it would have been in commercial airspace. For a spy device? Not likely. It's more likely that it WAS flying much higher and now is descending and at a lower altitude.
I see now it was shot down. Nice of the pResident to get rid of the evidence for the Chinese.