Originally Posted by
UAL T38 Phlyer
3. High-Speed Mach Buffet. When you approach the critical Mach of a wing, the airflow going over the top of the wing will speed-up to the point it is supersonic. This typically happens in a rapid on/off/on/off fashion, and is manifested as a rumble or buffet. It occurs because the temporarily supersonic air separates from the wing, then re-attaches...just like a conventional angle-of-attack stall.
The High Speed Buffet test was performed in-flight during a Post Maintenance test flight on B-727's coming out of a "D" Check. The purpose is to test the mach speed warning system all the way through the buffet.
After going through the Boeing school and having a Boeing test pilot riding along as a "reference", I've done this "test" under
controlled circumstances starting in the low 30,000'. Believe me, when the high speed buffet begins, there is
no doubt what is happening and one would not want to get into a high speed buffet near the coffin corner..... especially in a three-holer !
Ask "Hoot" Gibson for those who remember him and their adventures in a 727.
G'Day Mates
