For most jets, the use of reverse thrust to slow down in flight, where even possible, is extremely dangerous, and strictly prohibited.
Not so on the DC-8, which is certified for the safe in-flight use of reverse thrust on the two inboard engines throughout its entire flight envelope, and which, in fact, uses in-flight reversing as a standard part of a normal descent - this despite the severe disruption in-flight reversing causes to the airflow over the wing.
What is it about the DC-8 that makes it capable of safely using reverse thrust in flight, unlike other jets?