In the early 70's my employer started to do some business Sovietside, mostly in Poland, but my boss and another colleague did go to Russia at that time. I cannot remember where they went but it did involve an internal flight from Moscow by Aeroflot.
On the return trip they landed in Moscow and the passengers were commanded to remain seated. Two men, dressed in black hats and leather overcoats, boarded and my colleagues were told to identify themselves. Their passports were taken and they were then led off the aircraft to a large black car which then proceeded out of the airport and along miles of roads lined with fir trees you get in all the best 50's spy films. Not a word was spoken and they feared the worst.
Eventually, the car swept into another airport and right up to a BOAC aircraft, they were handed back their passports and, in perfect English, wished a happy flight back to London.