Originally Posted by
UAL T38 Phlyer
The "Soft cruise" technique (the autopilot uses small climbs/descents to control speed instead of constantly changing throttles; supposed to be less noticable to passengers, and less likely to cause an engine failure) is novel and works well...unless you get into an overspeed in mountain wave at FL390. A quirk, but I think a good tradeoff.
I think Alaska did that in the 1990's with their MadDog fleet. They let it wander plus or minus 200 feet in cruise, knowing that ATC computers won't detect the altitude change until it hits over 250 feet.
Not sure how smart that is in RVSM.