Casual. .. .Thanks for that. In commenting about the terms used in the US I did say it was a long time ago - 20 years actually - not 15 as I said, now I have looked in my logbook!. .. .The model I have in my head for pondering all these (many and complex) types of compressor aerodynamic events is a very simplified one, but it served me well when I was in the business and goes like this: . .. .When an engine is running, if any stage of the compressor suddenly drops its output pressure (whatever the cause) then there will be knock on effects for the stages behind and perhaps even in front. If those stages are themselves a bit near their aerodynamic limits then the disturbance is likely to spread very rapidly and in the end the combustion chamber pressure may not be prevented from relieving itself forwards. If on the other hand the first downstream stage is not particularly struggling there may be a chance to recover the situation without shutting the donk down. Most of the recoverable surges that I experienced (probably in the hundreds) could be sorted if you chopped the throttle quick enough after the first 'pop' or removed the cause of the trouble in the first place - often inlet flow distortion caused by excessive sideslip or incidence, especially when associated with too quick an accel or too much N over root theta due to a poorly adjusted PRL. . .. .Airframe type specific problems, caused by intake flow distortion, can themselves be very transient and as the engine starts to react can go away, making the pop an isolated and self recovering event even without reducing power. When establishing such manoeuvre related surge boundaries one could learn to yug to a high alpha, find the engine OK and yug then to a tad more and so on, until you just tickled a single pop. As opposed to going at it bull at a gate and have the first event become a locked in surge requiring shut down. . .. .Regards. .. .John Farley