The drag of a blunt body in a supersonic flow can be reduced by adding a so-called aerospike to the front surface of this body. The presence of this aerospike often leads to flow instability in the form of oscillations of the established shock pattern. This paper describes two complementary test series conducted to examine this instability in free-flight experiments as well as in supersonic tunnel tests with a stationary model. The results indicate that the observed oscillation patterns are identical within measurement accuracy, which also verifies that, at least for the test facilities used here, the instability is not influenced by facility-induced disturbances.